THESTAR

FORMATION

NEWSLETTER

An electronic publication dedicated to early stellar/planetary evolution and molecular clouds
No. 316 — 20 April 2018

Editor: Bo Reipurth (reipurth@ifa.hawaii.edu)

List of Contents
The Star Formation Newsletter
Editor: Bo Reipurthreipurth@ifa.hawaii.edu

Interview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
My Favorite Object . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Abstracts of Newly Accepted Papers . . . . . . . . . . 10

Associate Editor: Anna McLeod
anna.mcleod@berkeley.edu

Meetings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

Technical Editor: Hsi-Wei Yen
hwyen@asiaa.sinica.edu.tw

Short Announcements . . . . . . . . . . . . . . . . . . . . . . . . 50

Summary of Upcoming Meetings . . . . . . . . . . . . . 48

Editorial Board
Joao Alves
Alan Boss
Jerome Bouvier
Lee Hartmann
Thomas Henning
Paul Ho
Jes Jorgensen
Charles J. Lada
Thijs Kouwenhoven
Michael R. Meyer
Ralph Pudritz
Luis Felipe Rodrı́guez
Ewine van Dishoeck
Hans Zinnecker
The Star Formation Newsletter is a vehicle forfast distribution of information of interest for astronomers working on star and planet formationand molecular clouds. You can submit material
for the following sections: Abstracts of recently
accepted papers (only for papers sent to refereed
journals), Abstracts of recently accepted major reviews (not standard conference contributions), Dissertation Abstracts (presenting abstracts of new
Ph.D dissertations), Meetings (announcing meetings broadly of interest to the star and planet formation and early solar system community), New
Jobs (advertising jobs specifically aimed towards
persons within the areas of the Newsletter), andShort Announcements (where you can inform or request information from the community). Additionally, the Newsletter brings short overview articles
on objects of special interest, physical processes ortheoretical results, the early solar system, as wellas occasional interviews.

Newsletter Archive
www.ifa.hawaii.edu/users/reipurth/newsletter.htm

Cover Picture
CG 4 belongs to the system of cometary globulesthat are found in the Gum Nebula and pointing towards the massive stars γ Vel and ζ Pup. These
globules represent former cloud cores, which havebeen escavated from their more tenous parental
clouds. The globules are associated with 2. generation low-mass star formation triggered by the
expanding HII region and radiation pressure. Image obtained with ESO’s Very Large Telescope.
Image courtesy ESO

Submitting your abstracts
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Q; In 1993 came the famouns paper by Philippe André,
yourself, and Mary Barsony on Class 0 sources. What
was the genesis of that paper?

Derek Ward-Thompson
in conversation with Bo Reipurth

A: The genesis of the Class 0 paper was actually very interesting. Philippe had been working with radio data of
Ophiuchus and found a point source apparently just to
one side of Oph A, which had the VLA catalogue name of
VLA1623. He read my Oph A paper and wanted to knowwhether I had detected VLA1623 in any of my data. It
could still have been a background radio galaxy at thatpoint. So he wrote me an old-fashioned letter! International email was still in its infancy at that time andwas very flaky. We eventually managed to make contact
electronically and we realised that the UKIRT data were
too low resolution to definitively say whether VLA1623
had been detected. So we agreed to write a telescope
proposal for the still relatively new James Clerk Maxwell
Telescope in Hawaii, where the single pixel bolometer had
been moved to. Philippe had met Mary at a conference,and she had also expressed an interest in Ophiuchus, so
the three of us wrote the proposal together and went observing together. When we took the data we realised what
we had found – a very bright point source in the submillimetre that was by then known to have an energetic CO
outflow that had to be a young stellar object – but it wasinvisible in the infra-red! At the time the YSO classification system of Class I, II & III had just been proposed.
But it was clear that this object had to be more embedded(i.e. younger) than a Class I. We realised we had discovered a whole new class of objects that were not previously
known! Philippe said, almost as a joke, that we should
call the new class of objects Class 0. I remembered myclassical education and knew that there was no Roman
numeral zero, and so I agreed to this name straight away,
because I thought that it would make my old school Latinteacher turn in his grave! And so it was decided – before
we had even left the telescope control room. When we returned to sea level we drank champagne in the then Joint
Astronomy Centre kitchen. We knew the paper that weplanned to write would make a splash.

Q; What was your PhD about and who was your adviser?
A: My PhD was actually on the topic of magnetic fields
in spiral galaxies. I worked with Mike Scarrott in the
Durham Polarimetry Group, so I’ve always been interested in polarimetry and magnetic fields. However, after
my PhD I decided that I wanted to look at objects thatare a bit closer to home, so I decided to concentrate on
regions of star formation. At the time the IRAS data werestill relatively new, and I was determined to make images
from the IRAS time-stream data. In fact, I was part of thevanguard of folk making images from IRAS data (something the satellite was never originally intended to do),and ultimately this was taken up by IPAC on an industrial scale. Now the IRAS all-sky data are amongst theprettiest pictures in infra-red astronomy.
Q; You were among the first to use submillimetre observations of star forming regions. In 1989 you and your coworkers discovered the famous submillimetre source SM1in ρ Oph A. What is known about this source today?
A: For my first post-doc I worked with Ian Robson (whosubsequently became JCMT Director), when the newest
telescope opening up new windows was the JCMT, so I
jumped at the chance to use it. Continuum bolometer
detectors were becoming sensitive enough to see something, so we tested out a single-pixel bolometer at UKIRT– pointing it at ρ Oph A. We made the first continuum
image (built up point by point) of ρ Oph A and detecteda bright source which we named SM1 (sub-millimetre 1)
for the first detected sub-millimetre continuum source in
Oph A. Many people have referred to SM1 without everunderstanding why we called it that! Now we know far
more about this source. We know that it contains multiple sub-clumps, it is part of a shell around the S1 HIIregion, and we even know what its magnetic field looks likefrom SCUBA2 polarimeter and SOFIA HAWC+ data.

Q; Another highly cited paper from around the same timedealt with submm observations of ‘star-less’ cores. What
were your key conclusions?
A: After VLA1623, I began to wonder if there was anything younger that we could see with our new-found submillimetre continuum sensitivity. At the time Phil Myers and co-workers had mapped a number of Lynds Dark
Clouds in CO and ammonia, and had cross-referenced thiswith the IRAS point source catalogue, which detected all
Class I, II & III sources. So I proposed to point the JCMT
at a large number of clouds that had ammonia detections
but no IRAS point sources to see what we could see. Because of the mismatch in resolution I didn’t know exactly3where to point the JCMT within the ammonia cores (there
was still only one pixel in our camera), so I hit on the idea
of mapping the cores in 13 CO (which was quicker thanmapping in the continuum), and then pointing the bolometer at the 13 CO peak, and mapping around it. Sometimes
I detected nothing at all. Sometimes I missed the continuum peak altogether, due to optical depth effects. But
fortunately the time allocation committee kept faith inme, and I managed to map about half a dozen of them inthe continuum. It was clear straight away that these werevery different from Class 0 sources. They were clearly extended, they had no jets or outflows, yet they had masses
consistent with being at least virialised when compared totheir ammonia line-widths. So I started by calling thempre-proto-stellar cores to indicate that they were at thestill earlier evolutionary stage. Eventually I realised thatlife was too short to be saying ‘pre-proto-stellar cores’ several times a day, so I shortened it to ‘pre-stellar cores’, andthe name stuck.

Q; With the launch of the Herschel Space Telescope, a newtool became available for the study of star formation. How
do Herschel and SCUBA-2 compare?
A: So, as a result of the afore-mentioned plotting, we had
two massive data-sets to play with. The SPIRE camera on Herschel (of which I was by then a member ofthe consortium) was mapping huge swathes of the sky,with incredible dynamic range. It got everything from thebright, dense, nearby regions, to the inter-stellar cirrus,
foreground asteroids, and back-ground high-Z galaxies –all in one frame! In a sense, it became a victim of its
own success – how did you work out what was associatedwith your star-forming region that you were studying? In
many regions, such as our ‘control’ region around Polaris,
the limitation on signal to noise was nothing to do with
the instrument – it was actually the density of faint background high-Z galaxies! This, of course, was why SPIRE
was so successful, and the team that built it won an award
from the RAS. But it left us with the problem of (in ourcase) how to determine what was a gravitationally boundpre-stellar core, and what was ‘chaff’. That was when
SCUBA-2 came riding to our rescue. In our paper on thecomparison between SCUBA-2 and SPIRE data in Taurus (W-T et al, 2016, MN, 463, 1008), we showed that,in a 3-colour composite SCUBA-2 and SPIRE image, thepre-stellar cores were pickled out perfectly by SCUBA-2– see the beautiful red objects in Figure 1 of that paper.
We went on to quantify the effect, in that anything above
104 cm−3 was detected by SCUBA-2 at the distance ofTaurus (Fig. 8), and we showed how this detection limit
should scale with distance and temperature for the whole
Herschel Gould Belt Survey.

Q; You have been involved with the JCMT Gould Belt
Legacy Survey using the, at the time, new SCUBA-2 submm imager. How did that arise?
A: Once SCUBA came along, it absolutely revolutionised
the field. We were able to take real pictures in real time.
And then there was SCUBA-2, and suddenly it was asif the CCD era had reached the submm. The mapping
speed and sensitivity increased by orders of magnitude,
and we were able to contemplate key programmes oververy large area surveys. The whole Gould Belt Programmewith every telescope imaginable came about as a resultof a lunch-time drink at a conference in Cambridge (theEnglish one) with Philippe. He was already heavily involved with Herschel at that time, and I was only justbecoming involved. He told me he had this plan to map
every nearby star-forming region with Herschel, and was
quizzing me about the potential ability of the almost finished camera for JCMT at that time, SCUBA-2. I confirmed that it could do the same. So we agreed that after
we had parted, he would go back and persuade the Herschel community that his was a good plan, and I would
do likewise in the JCMT community, which at that time
included the UK, Canada and the Netherlands. Shortly
after that I was at a conference in Aspen, Colorado, having
a drink, this time with Doug Johnstone, and I got him on
board with the plan. He went home and persuaded his pal
James Di Francesco, and not long afterwards, at a meetingin the Netherlands, James and I got Michiel Hogerheijde
and Jenny Hatchell on board, after which the rest of the
JCMT community was delighted to join in. Thereafter,
every self-respecting telescope had to have a Gould Belt
Survey. So the message to younger readers is not to underestimate the value of the social time around conferences –that’s where all the best plans are born!

Q; Most recently you and your collaborators have presented
first results from the polarimeter POL-2 on SCUBA-2,
casting light on magnetic fields in starforming regions.
What is the potential of this instrument?
A: POL-2 on SCUBA-2 is a simply fantastic instrument.
Our BISTRO survey (448 hours of JCMT time) is absolutely gobbling up the Gould Belt, and we are churning out
the results. But the best is still to come. The first part ofthe survey – BISTRO1 – has now completed all observations, and the second part – BISTRO2 – is half-complete.
But the data reduction is still ongoing, and only the firsthalf-dozen regions have been published so far. However,
we’ve already seen some spectacular results in Orion, Oph
A, Oph B, Oph C, IC5146, and, above all, the ‘Pillars ofCreation’. The rest of the data are being analysed as we
speak, and the rest of the papers will be published thickand fast. So this is one case where I can quite literally say– watch this space!

4

can also impact the formation of low mass stars and browndwarfs (Stamatellos & Whitworth 2009) as well as the finalarchitecture of planetary systems (Hubbard, 2017).

My Favorite Object
Gaia 17bpi: The latest FUor
outburst
Carlos Contreras Peña

Most eruptive variable YSOs have historically been classified based on the photometric and spectroscopic characteristics of the observed outburst. They are classified aseither EXors, which typically show less dramatic changes
in the accretion rate and have outburst durations of weeks
to months, with a maximum of 1.5 yr (Herbig, 2008),
or FUors, which have long-duration outbursts (typicallydecades but at least 10 yr) and with accretion rates thatcan reach 10−4 M⊙ yr−1 (Audard et al. 2014). With
the advent of dedicated optical and near-infrared multiepoch surveys, there has been an increase of discoveries
with time (Hillenbrand et al. 2018). The more recent
additions to the eruptive variable class have shown characteristics that make a classification as FUors or EXors
difficult (see e.g. Contreras Peña et al. 2017b, Hillenbrand
et al. 2019)

YSOs displaying FUor-like outbursts share clear spectroscopic signatures, such as P Cygni profiles in specific lines,
the gradually cooler spectra at longer wavelengths, and the
low-gravity spectral appearance (Connelley & Reipurth2018). In these objects the spectral energy distribution
1 Introduction(SED) is dominated by a disk accreting at rates of ∼10−4 M⊙ yr−1 . In steady-accretion disk models the efI have always been fascinated by the study of variable fective temperature of the disk varies with radius. Then,stars, and ever since my PhD I have dedicated my time to observations at longer wavelengths will be sensitive to theresearch rare, but incredible, eruptive young stellar objects outer, cooler disk regions, which explains the variation of(YSOs).
the spectral type with wavelength (Hartmann & Kenyon,
The large and sudden brightness changes in these objects 1996).
are thought to occur due to changes in the accretion rate Many aspects of the young eruptive YSOs are still uncerof up to 3 orders of magnitude, going from the typical T tain. The frequency and amplitude of the outbursts are
Tauri rates of 10−7 M⊙ yr−1 up to 10−4 M⊙ yr−1 , with not well constrained (see e.g. Scholz et al. 2013., Hillenoutburst lasting from weeks up to about 100 years, which brand & Findeisen, 2015). In addition, there is controcan increase the central luminosity to 100 L⊙ , dumping versy as to whether the very largest FUor outbursts occur
as much as 0.01 M⊙ onto the central star in one out- across all stages of young stellar evolution or are just limburst (see e.g. Hartmann & Kenyon, 1996). Disk instabil- ited to the class 0/I phase (c.f. Sandell & Weintraub, 2001,
ities such as gravitational instabilities (Vorobyov & Basu, Miller et al. 2011).
2005), planet-induced thermal instabilities (e.g. Lodato &With the aim of determining the frequency of long-lasting,Clarke 2004) or instabilities due to interactions in a bilarge outbursts and whether they are associated with thenary system (Bonnell & Bastien, 1992), are suggested asplanet-building phase (class II stage) at all, we have been
explanations of the large variability.
monitoring a large sample of known YSOs using the Gaia
It is thought that highly variable accretion may be com- all-sky photometric survey. The Gaia consortium is pubmon amongst protostars, though rarely observed owing to lishing prompt alerts and light curves for stars seen toa duty cycle consisting of long periods of slow accretion vary in the Gaia data stream1 . The automated transientand much shorter periods of unstable accretion at a much discovery is conducted down to V ∼ 19 and is based onhigher rate. If this is true, it might explain both the ob- either detection of a new source, or a significant deviation
served under-luminosity of low-mass, class I YSOs (the in brightness of a known source compared with previous“Luminosity problem”; see e.g. Kenyon et al. 1990; Evans Gaia measurements (Hodgkin et al. 2013; S. T. Hodgkin
et al. 2009) and the wide scatter seen in the Hertzsprung- et al. 2019, in preparation).
Russell diagrams of pre-main-sequence (PMS) clusters (e.g.
1 http://gsaweb.ast.cam.ac.uk/alerts/alertsindex
Baraffe et al. 2012). The episodes of enhanced accretion5

2

Finding FUors

mation, hence clustered on the sky, we can also identify
YSOs using what we term a “vicinity match”. When an
alert is not successfully cross-matched with any specificobject in the search catalogs, but it is located within 2
arcminutes of a confirmed or candidate YSO, the object
is still added as a possible YSO-related alert.

Finding FUors in multi-epoch photometric surveys such as
Gaia is difficult. FUors are rare, as there are fewer than 17
recorded outbursts (see e.g. Connelley & Reipurth, 2018),
and although episodic accretion is thought to be universal
amongst YSOs, the recurrence timescale of these events is To determine whether the observed variability of a YSO
yet unclear (see Section 1).
relates to the FUor phenomenon, we must be able to obIn addition, high-amplitude variability in YSOs is not ex- tain two or more epochs of photometric and/or spectroclusively due to large changes in the accretion rate. In my scopic monitoring after an alert has been flagged as being
previous work with the Vista Variables of the Via Lactea related to a likely YSO. Multi-colour photometry at difsurvey (VVV, Minniti et al. 2010), I found a large sample ferent brightness levels allows us to identify whether theof high-amplitude (∆Ks > 1 mag) variable YSOs (Con- observed variability is related to variable accretion or totreras Peña et al. 2017a). A high-amplitude cut avoids other known mechanisms that drive large amplitude variselecting YSOs where variability is driven by “typical” ability in YSOs. For example changes in the extinction
mechanisms such as for example cold or hot spots on along the line of sight show a very distinctive behaviour
the stellar photosphere (e.g. Scholz, 2012) or changes in in both colour-magnitude and colour-colour diagrams (seedisk parameters (Meyer et al. 1997). However, selecting e.g. Froebrich et al. 2018). In addition, the use of spechigh-amplitude variable stars as showing accretion-related troscopy is desirable to confirm that the alert shows theoutbursts, based only on photometric information has the characteristics of YSOs in high states of accretion, as theserisk of selecting objects with light curves that can mimic objects show distinct characteristics in their optical andsuch outbursts, especially if the light curve sampling is near-infrared spectra (see Section 1).
sparse. At this high-amplitude level (extreme) cases of
hot-spot variability and variable extinction can also explain the observed variability in YSOs (Contreras Peñaet al. 2017a). Since changes in the extinction along theline of sight can produce variability with amplitudes thatare effectively limitless, as it depends on the amount of
dust that obscures the star, it is not hard to imagine
that objects brightening from high-amplitude, long-lasting
eclipses by inhomogeneities at long distances in the accretion disk (e.g. AA Tau) or a precessing disk in a binary
system (e.g. KH 15D, Aronow et al. 2018) could mimic an
FUor outburst.
The number of FUor outburst we expect to observe, Nfuor ,depends on the number of YSOs surveyed, NYSO , the baseline of observations, ∆t, and the recurrence timescale ofoutbursts, r, with Nfuor = rNYSO ∆t (see Hillenbrand &Findeisen, 2015). Since the recurrence timescale of outbursts is not well constrained, the only way to increase
our chances of detecting FUor outbursts, given the baseline of Gaia observations (∆t ∼ 3 yr), is to monitor thethe largest possible sample of YSOs (See Figure 3 in Hillenbrand & Findeisen, 2015). With this objective in mind
we have assembled a catalogue of approximately 20,000
YSOs. These have SuperCOSMOS (SSS, Hambly et al.
2001) magnitudes which we can fold through the Gaia
bandpass to show that they are bright enough (G < 20)
to trigger Gaia alerts if they change significantly in magnitude. In addition we also acknowledge the fact that thecurrent membership lists for many nearby star-forming regions remains incomplete. If we take into account thatYSOs are located in spatially coherent regions of star for-Figure 1: Portion of the Liverpool Telescope spectra ofGaia 17bpi at R = 350. From bottom to top, representing
three different nights during the light curve rise. NaD and
Hα absorption appears and strengthens.

3

Discovery of Gaia 17bpi

Gaia 17bpi was announced on the Gaia alerts public feedon June 23, 2017. The alert was triggered as a “deltamagnitude detection”, i.e. a source brightening relative toearlier Gaia photometry by >1 mag in two consecutive
transits of the satellite over the source position (in Marchand then June, in this case). Gaia 17bpi was not successfully cross-matched with any specific object in the search6catalogs, but it was identified as a “vicinity match” as
it has five YSOs falling in the vicinity of the alert coordinates, located at separations between 75 to 177 arcsec
from the variable star.

4

Follow-up

We obtained griz photometry as well as low-resolution(R = 350) spectroscopy using the IO:O and SPRAT instruments, respectively, at the Liverpool telescope (Steele
et al. 2004) 6 days after the alert was published, and then 3months later when the object had become one magnitude
brighter.

The early doubts
The low-resolution spectra at these two epochs appearedfeatureless (see middle and bottom spectra in Fig. 1).
There was some evidence of absorption features from NaD
and Hα, however these were hard to tell apart from thenoisy spectrum. The colour change between these two
epochs appeared consistent with variable extinction.
Figure 2: Portion of the Palomar/TripleSpec spectrumof Gaia 17bpi. The spectrum is similar to that of an Mtype photosphere, mainly due to the prominent H2 O broad
depressions in the H band and K band and the 12 CO (2−0)
bandhead absorption in the K band. The spectrum agrees
well with the set of FU Ori objects displayed in Figure 3
of Connelley & Reipurth (2018).

We collected ancillary data from the 2MASS (Cutri etal. 2003) and Spitzer/GLIMPSE (Churchwell et al. 2009)
catalogs. In the latter, Gaia 17bpi only had detections
at 3.6 and 4.5 µm. From these data alone we could notmeasure the infrared excess expected in YSOs. In fact theSED of Gaia 17bpi up to 4.5 µm is not dissimilar from a
reddened stellar photosphere (see Section 5). In addition,
while the light curve of Gaia 17bpi exhibits an FU Ori-like
rise, several classes of large-amplitude pulsating variables
have similarly slow rise times, as do active galactic nuclei.
Some doubt also arose from the fact that the closest known
YSO to Gaia 17bpi was located more than 1 arcmin fromthe alert.

to confirm Gaia 17bpi as a member of the FUor class. We
then alerted other members of the collaboration of the existence of this object. They obtained additional photometric and spectroscopic observations I describe below which
covered optical to near-infrared wavelengths and that were
Therefore analysis of these two epochs, along the addi- fundamental to study the nature of Gaia 17bpi.
tional information discussed above, lead to Gaia 17bpi beWe obtained an optical Keck/DEIMOS (Faber et al. 2003)
ing flagged as potentially a non-YSO alert.
spectrum (4630-9865 Å, R ≃ 2200) and a near-infrared
Confirmation(10000-25000 Å, R = 2700) Palomar TripleSpec (Herter
et al. 2008) spectrum of Gaia 17bpi on 2018 September
The Gaia light curves of alerts that are classified this way
10, and 25, respectively. The DEIMOS spectrum conare still updated frequently. This allows the possibility offirmed the features observed in the third SPRAT specdetermining whether there are any changes in the phototrum, with numerous strong P-Cygni-type blueshifted abmetric properties that would change the classification ofsorption lines in NaD, Hα, and the Ca II triplet, consisthe alert. In the case of Gaia 17bpi we noticed that thetent with an F-type spectrum. The TripleSpec spectrum
object had continued to increase its brightness by over a
showed 12 CO absorption in the 2.3µm region and promimagnitude and had reached an apparently stable brightnent H2 O absorption in the K band and H band, similarstate. Considering this we obtained a third epoch of photo an M-type spectrum (see Fig. 2).
tometry and spectroscopy on August 23 2018, more thana year after the alert was published. The third epoch of These two observations also confirm a key feature of classic
low-resolution spectra showed distinct absorption features FUor outbursts, which is the change in the spectral typewith wavelength. Therefore making Gaia 17bpi the latestof NaD and Hα (see top spectrum in Fig. 1).
addition to the FUor class.
These features alone, although promising, were not enough7

Figure 3: False colour image constructed from 3.6 µm(blue), 4.5 µm (green) and 8.0 µm (red) data from
GLIMPSE-I. The location of Gaia 17bpi is marked by thewhite diamond. Green circles mark the location of infraredexcess sources selected from 2MASS/Sptizer colours. Finally, the inset shows an expanded view 4.5×4 arcmin
Figure 4: Spectral energy distribution of Gaia 17bpi. Redin size illustrating the adjacent small HII region HRDS
points are the post-outburst data, while black points are
G053.822-00.057.
the assembled pre-outburst photometry with black downward triangles indicating upper limits. Also shown are
reddened model photospheres normalized at z band to the
5 Characteristics
pre-outburst photometry.
In the following I summarise some of the characteristics
of Gaia 17bpi. For a more detailed information I refer theject is also apparent, although faint. Gaia 17bpi is notreader to Hillenbrand et al. (2018).
observed in MIPS and Herschel images. We performed
The Star-Forming region. Gaia 17bpi is associated aperture photometry at the location of the object, wherewith a previously faint optical (r < 22 mag), near-infrared, MIPS and Herschel measurements correspond to upperand mid-infrared point source. The position (see Fig. 3) limits (see Fig. 4).
is located toward the northern end of the elongated G53.2
Photospheric models ranging in temperature from 2900
infrared dark cloud (IRDC) just outside of a particularly
to 4500 K result in acceptable fits to the Wien part ofopaque region on optical and infrared images, and adjacent
the SED for corresponding visual extinction values of 1
to a small H II region cataloged as HRDS G053.822- 00.057
to 5 mag. Integrating the pre-outburst photometry be(Anderson et al. 2014). The modest star-forming region
tween 0.45 and 4.5 µm, and assuming the 1.27 kpc disis hardly studied. To estimate the distance to Gaia 17bpi
tance, a source luminosity of 0.3 L⊙ is derived for the
we used Spitzer/GLIMPSE, 2MASS, and Gaia DR2 (Gaia
pre-outburst object. This luminosity is appropriate for a
Collaboration et al. 2018) catalogs, and identified infraredpre-main-sequence star in the 2900-4500 K temperatureexcess sources that are likely YSOs by using the colour
range. The corresponding spectral type would be mid-K
criteria of Gutermuth et al. (2009). The cloud distanceto M.
was then estimated by examination of the Gaia parallax
distribution of the infrared excess sources. A weighted Mid-infrared outburst. The position of Gaia 17bpi wasobserved at mid-infrared wavelengths as part GLIMPSE inmedian approach yields a distance of 1270+80−70 pc.
late 2004, and there is a second set of IRAC 3.6 and 4.5 µm
The spectral energy distribution. The SED of theimaging data, taken in 2014 December, where the nearby
pre-outburst object was assembled from catalog data originfrared dark cloud was targeted twice (program 10012,
inating from the Gaia DR2, PanSTARRS DR1 (Flewelling
PI: J. Hora). The position was also observed by WISE
et al. 2016), IPHaS (Barentsen et al. 2014), 2MASS, and(Wright et al. 2010) in 2010 April and October, and again
Spitzer/GLIMPSE-I surveys, with additional use of imtwice per year between 2014 October and 2018 Octoberages from IRAC (3.6, 4.5, 5.8, 8µm), MIPS (24, 70µm),
during the NEOWISE survey (Mainzer et al. 2014). Gaia
and all Herschel data (70, 160 , 250, 350, 500 µm). The
17bpi was not detected in the WISE observations. The
GLIMPSE-I catalog only contains measurements at thesource is, however, well detected at 3.4 and 4.6 µm in thetwo shortest wavelengths (3.6 and 4.5 µm) for Gaia 17bpi.
NEOWISE observations beginning in 2015 April.
Inspection of 5.8 and 8.0 µm images showed that the ob8

temporaneous multi-epoch surveys covering a wide range
in wavelength (Gaia, VVV+VVVX, WISE+NEOWISE)
in our understanding of the disk instabilities that drive
the dramatic changes in the accretion rates of YSOs. In
this sense, we will continue to monitor the outburst ofGaia 17bpi over a wide wavelength range by using Gaia(the light curves of past alerts are regularly updated by
the Gaia consortium) and Spitzer, where we have recently
been awarded time to follow-up the FUor with IRAC.
Acknowledgements
The discovery of Gaia 17bpi as a new member of the FUor classwould have not been possible without the large collaboration between institutes in the UK and at Caltech. In this sense I would liketo thank my co-authors Lynne Hillenbrand, Sam Morrell, Tim Naylor, Dirk Froebrich. Michael Kuhn, Roc Cutri, Luisa Rebull, Simon
Hodgkin and Amy Mainzer. We are also grateful to Evan Kirby andto the Palomar Observatory staff.

Figure 5: (top) Optical and mid-infrared light curve ofGaia 17bpi. (bottom) Zoom-in of the first epochs of Gaia
photometry taken in late 2015. The variability of Gaia
17bpi has an amplitude of a few tenths of a mag with atimescale of a few days, consistent with the typical variability of T Tauri stars (see e.g. Cody & Hillenbrand 2018).

References:
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The light curve (Figure 5) suggests that the outburst may
have started in the infrared and appeared later in the optical. As we do not sample the beginning of the burst in
the optical, given the large time gap between the initialand subsequent Gaia photometry, we cannot calculate thetime delay, but ∼1.5-2 yr is implied. The NEOWISE light
curve further indicates a possible two-stage rise, with ∼ 18
months of mid-infrared brightening, followed by a plateau
of about a year, then another at least 24 months of midinfrared brightening corresponding to the optical rise thatis well sampled by the Gaia measurements.

6

Final thoughts

The fact that Gaia 17bpi was originally selected as a “vicinity match” indicates that there is a large population of
YSOs that are too faint for current and past photometricsurveys. This is supported by the fact that the number ofhigh-amplitude variable YSOs increases as we go towards
fainter magnitudes (Contreras Peña et al. 2017a). Given
this, the future multi-epoch Large Synoptic Survey Telescope (LSST) survey, which will go 5 magnitudes deeper
than Gaia, will provide a large number of FU Ori outbursts.
Gaia 17bpi is also unique among FU Ori outbursts inhaving its photometric brightening detected at both optical and mid-infrared wavelengths. The burst appears tohave started in the infrared, consistent with disk models
that predict instabilities in the inner 0.5-1 au of protostellar and T Tauri accretion disks as the origin of FU Ori
events. This demonstrates the importance of having con9

Abstracts of recently accepted papers

1

On the mass accretion rate and infrared excess in Herbig Ae/Be Stars
R. Arun1 , Blesson Mathew1 , P. Manoj2 , K. Ujjwal1 , Sreeja S. Kartha1 , Gayathri Viswanath1 , Mayank
Narang2 and K.T. Paul1
1

Department of Physics and Electronics, CHRIST, Bangalore 560029, India; 2 Department of Astronomy and Astrophysics, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400005, India
E-mail contact: blesson.mathew at christuniversity.in

The present study makes use of the unprecedented capability of the Gaia mission to obtain the stellar parameterssuch as distance, age, and mass of HAeBe stars. The accuracy of Gaia DR2 astrometry is demonstrated from thecomparison of the Gaia DR2 distances of 131 HAeBe stars with the previously estimated values from the literature.
This is one of the initial studies to estimate the age and mass of a confirmed sample of HAeBe stars using both thephotometry and distance from the Gaia mission. Mass accretion rates are calculated from Hα line flux measurementsof 106 HAeBe stars. Since we used distances and the stellar masses derived from the Gaia DR2 data in the calculationof mass accretion rate, our estimates are more accurate than previous studies. The mass accretion rate is found to
decay exponentially with age, from which we estimated a disk dissipation timescale of 1.9 ± 0.1 Myr. Mass accretion
rate and stellar mass exhibits a power law relation of the form, Ṁacc ∝ M⋆ 2.8±0.2 . From the distinct distribution in
the values of the infrared spectral index, n2−4.6 , we suggest the possibility of difference in the disk structure between
Herbig Be and Herbig Ae stars.
Accepted by AJ
http://arxiv.org/pdf/1903.01070

2

Building protoplanetary disks from the molecular cloud: redefining the disk timeline
K. Baillié1,2, J. Marques3 , and L. Piau1
1

IMCCE, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universits, UPMC Univ Paris 06, Univ.
Lille, 77 Av. Denfert-Rochereau, 75014 Paris, France; 2 Centre National d’Études Spatiales, 2 place Maurice Quentin,
75039 Paris Cedex 01, France; 3 Univ. Paris-Sud, Institut d’Astrophysique Spatiale, UMR 8617, CNRS, Batiment121, 91405, Orsay Cedex, France
E-mail contact: kevin.baillie at obspm.fr
We study the formation of the protoplanetary disk by the collapse of a primordial molecular cloud, and how its
evolution leads to the selection of specific types of planets. We use a hydrodynamical code that accounts for the
dynamics, thermodynamics, geometry, and composition of the disk to numerically model its evolution as it is fedby the infalling cloud material. As the mass accretion rate of the disk onto the star determines its growth, we cancalculate the stellar characteristics by interpolating its radius, luminosity, and temperature over the stellar mass frompre-calculated stellar evolution models. The density and midplane temperature of the disk then allow us to model theinteractions between the disk and potential planets and determine their migration.
At the end of the collapse phase, when the disk reaches its maximum mass, it pursues its viscous spreading, similarly
to the evolution from a minimum mass solar nebula (MMSN). In addition, we establish a timeline equivalence between
the MMSN and a “collapse-formed disk” that would be older by about 2 Myr.
We can save various types of planets from a fatal type-I inward migration: in particular, planetary embryos can avoid
falling on the star by becoming trapped at the heat transition barriers and at most sublimation lines (except thesilicates one). One of the novelties concerns the possible trapping of putative giant planets around a few astronomical
units from the star around the end of the infall. Moreover, trapped planets may still follow the traps outward during
the collapse phase and inward after it. Finally, this protoplanetary disk formation model shows the early possibilitiesof trapping planetary embryos at disk stages that are anterior by a few million years to the initial state of the MMSN
10

approximation.
Accepted by A&A
http://arxiv.org/pdf/1903.03540

3

Protoplanetary Disk Masses from Radiative Transfer Modeling: A Case Study in Taurus
Nicholas P. Ballering1 and Josh A. Eisner1
1

Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA

E-mail contact: ballerin at email.arizona.edu
Measuring the masses of protoplanetary disks is crucial for understanding their planet-forming potential. Typically,
dust masses are derived from (sub-)millimeter flux density measurements plus assumptions for the opacity, temperature, and optical depth of the dust. Here we use radiative transfer models to quantify the validity of these assumptions
with the aim of improving the accuracy of disk dust mass measurements. We first carry out a controlled explorationof disk parameter space. We find that the disk temperature is a strong function of disk size, while the optical depth
depends on both disk size and dust mass. The millimeter-wavelength spectral index can be significantly shallower than
the naive expectation due to a combination of optical depth and deviations from the Rayleigh-Jeans regime. We fit
radiative transfer models to the spectral energy distributions (SEDs) of 132 disks in the Taurus-Auriga region usinga Markov chain Monte Carlo approach. We used all available data to produce the most complete SEDs used in any
extant modeling study. We perform the fitting twice: first with unconstrained disk sizes and again imposing the disk
size–brightness relation inferred for sources in Taurus. This constraint generally forces the disks to be smaller, warmer,
and more optically thick. From both sets of fits, we find disks to be ∼1–5 times more massive than when derived using(sub-)millimeter measurements and common assumptions. With the uncertainties derived from our model fitting, thepreviously measured dust mass–stellar mass correlation is present in our study but only significant at the 2σ level.
Accepted by AJ
http://arxiv.org/pdf/1903.08283

4Young massive star cluster formation in the Galactic Centre is driven by global gravitational collapse of high-mass molecular clouds
A. T. Barnes1 , S. N. Longmore2 , A. Avison3 , Y. Contreras4 , A. Ginsburg5 , J. D. Henshaw6 , J. M.
Rathborne7 , D. L. Walker8 , J. Alves9 , J. Bally10 , C. Battersby11 , M. T. Beltrn12 , H. Beuther6 , G.
Garay13 , L. Gomez8 , J. Jackson14 , J. Kainulainen15 , J. M. D. Kruijssen16 , X. Lu17 , E. A. C. Mills18 , J.
Ott5 and T. Peters19
1
Argelander-Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, 53121, Bonn, Germany; 2 Astrophysics
Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF, UK; 3 UK Atacama
Large Millimeter/submillimeter Array Regional Centre Node; 4 Leiden Observatory, Leiden University, PO Box 9513,
NL-2300 RA Leiden, Netherlands; 5 National Radio Astronomy Observatory, 1003 Lopezville Rd., Socorro, NM,
87801, USA; 6 Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany; 7 CSIRO Astronomy
and Space Science, P.O. Box 76, Epping NSW, 1710, Australia; 8 Joint ALMA Observatory, Alonso de Crdova 3107,
Vitacura, Santiago, Chile; 9 University of Vienna, Department of Astrophysics, Türkenschanzstrassee 17, 1180 Vienna,
Austria; 10 CASA, University of Colorado, 389-UCB, Boulder, CO, 80309, USA; 11 Department of Physics, Universityof Connecticut, Storrs, CT, 06269 USA; 12 INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze,
Italy; 13 Departamento de Astronomia, Universidad de Chile, Casilla 36-D, Santiago, Chile; 14 SOFIA Science Center,
USRA, NASA Ames Research Center, Mountain View, CA, 94043, USA; 15 Chalmers University of Technology,
Onsala Space Observatory, 439 92 Onsala, Sweden; 16 Astronomisches Rechen-Institut, Zentrum für Astronomie derUniversität Heidelberg, Münchhofstrasse 12-14, 69120 Heidelberg, Germany; 17 National Astronomical Observatoryof Japan, 2-21-1 Osawa, Mitaka,Tokyo, 181-8588, Japan; 18 Physics Department, Brandeis University, 415 South
Street, Waltham, MA, 02453, USA; 19 Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Strassee 1, D-85748
Garching, Germany

E-mail contact: ashleybarnes.astro at gmail.com
Young massive clusters (YMCs) are the most compact, high-mass stellar systems still forming at the present day. The
11

precursor clouds to such systems are, however, rare due to their large initial gas mass reservoirs and rapid dispersal
timescales due to stellar feedback. Nonetheless, unlike their high-z counterparts, these precursors are resolvable down
to the sites of individually forming stars, and hence represent the ideal environments in which to test the current
theories of star and cluster formation. Using high angular resolution (1′′ / 0.05pc) and sensitivity ALMA observationsof two YMC progenitor clouds in the Galactic Centre, we have identified a suite of molecular line transitions – e.g.
c-C3 H2 (7 − 6) – that are believed to be optically thin, and reliably trace the gas structure in the highest density gas on
star-forming core scales. We conduct a virial analysis of the identified core and proto-cluster regions, and show that halfof the cores (5/10) and both proto-clusters are unstable to gravitational collapse. This is the first kinematic evidenceof global gravitational collapse in YMC precursor clouds at such an early evolutionary stage. The implications arethat if these clouds are to form YMCs, then they likely do so via the “conveyor-belt” mode, whereby stars continuallyform within dispersed dense gas cores as the cloud undergoes global gravitational collapse. The concurrent contractionof both the cluster-scale gas and embedded (proto)stars ultimately leads to the high (proto)stellar density in YMCs.
Accepted by MNRAS
http://adsabs.harvard.edu/pdf/2019arXiv190306158B

5

Dust traps in the protoplanetary disc MWC 758: two vortices produced by two giant
planets?
Clément Baruteau1 , Marcelo Barraza2,3,7 , Sebastián Pérez2,3 , Simon Casassus2,3 , Ruobing Dong4 , Wladimir
Lyra5,6 , Sebastián Marino7 , Valentin Christiaens2,3,8 , Zhaohuan Zhu9 , Andrés Carmona1 , Florian Debras1
and Felipe Alarcon2,3
1

IRAP, Université de Toulouse, CNRS, UPS, Toulouse, France; 2 Departamento de Astronomı́a, Universidad de Chile,
Casilla 36-D, Santiago, Chile; 3 Millennium Nucleus ’Protoplanetary Disks’, Chile; 4 Steward Observatory, Universityof Arizona, Tucson, AZ, 85719, USA; 5 Department of Physics and Astronomy, California State University Northridge,
1811 Nordhoff St, Northridge CA 91130, USA; 6 Jet Propulsion Laboratory, California Institute of Technology, 4800
Oak Grove Drive, Pasadena, CA, 91109, USA; 7 Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg, Germany; 8 Monash Centre for Astrophysics (MoCA) and School of Physics and Astronomy, Monash University,
Clayton Vic 3800, Australia; 9 Department of Physics and Astronomy, University of Nevada, Las Vegas, 4505 South
Maryland Pkwy, Las Vegas, NV 89154, USA
E-mail contact: clement.baruteau at irap.omp.eu
Resolved ALMA and VLA observations indicate the existence of two dust traps in the protoplanetary disc MWC 758.
By means of 2D gas+dust hydrodynamical simulations post-processed with 3D dust radiative transfer calculations,
we show that the spirals in scattered light, the eccentric, asymmetric ring and the crescent-shaped structure in the(sub)millimetre can all be caused by two giant planets: a 1.5-Jupiter mass planet at 35 au (inside the spirals) and a
5-Jupiter mass planet at 140 au (outside the spirals). The outer planet forms a dust-trapping vortex at the inner edgeof its gap (at ∼85 au), and the continuum emission of this dust trap reproduces the ALMA and VLA observations
well. The outer planet triggers several spiral arms which are similar to those observed in polarised scattered light. The
inner planet also forms a vortex at the outer edge of its gap (at ∼50 au), but it decays faster than the vortex inducedby the outer planet, as a result of the disc’s turbulent viscosity. The vortex decay can explain the eccentric inner ring
seen with ALMA as well as the low signal and larger azimuthal spread of this dust trap in VLA observations. Finding
the thermal and kinematic signatures of both giant planets could verify the proposed scenario.
Accepted by MNRAS
http://arxiv.org/pdf/1903.06537

6

Discrepancies in the ages of young star clusters; evidence for mergers?
Emma R. Beasor1 , Ben Davies1 , Nathan Smith2 and Nate Bastian1
1

Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF, UK; 2
Steward Observatory, University of Arizona, 933 N. Cherry Ave., Tucson, AZ 85721, USA
E-mail contact: e.beasor at 2010.ljmu.ac.uk
There is growing evidence that star clusters can no longer be considered simple stellar populations (SSPs). Intermediate12and old age clusters are often found to have extended main sequence turn-offs (eMSTOs) which are difficult to explain
with single age isochrones, an effect attributed to rotation. In this paper, we provide the first characterisation of thiseffect in young (<20 Myr) clusters. We determine ages for 4 young massive clusters (2 LMC, 2 Galactic) by threedifferent methods: using the brightest single turn-off (TO) star; using the luminosity function (LF) of the TO; andby using the lowest Lbol red supergiant (RSG). The age found using the cluster TO is consistently younger than theage found using the lowest RSG Lbol . Under the assumption that the lowest luminosity RSG age is the ‘true’ age, we
argue that the eMSTOs of these clusters cannot be explained solely by rotation or unresolved binaries. We speculatethat the most luminous stars above the TO are massive blue straggler stars formed via binary interaction, either as
mass gainers or merger products. Therefore, using the cluster TO method to infer ages and initial masses of post-main
sequence stars such as Wolf-Rayet stars, luminous blue variables and RSGs, will result in ages inferred being too young
and masses too high.
Accepted by MNRAS
http://arxiv.org/pdf/1903.05106

7

Photometric determination of the mass accretion rates of pre-main sequence stars.
VI. The case of LH 95 in the Large Magellanic Cloud
Katia Biazzo1 , Giacomo Beccari2 , Guido De Marchi3 and Nino Panagia4
1

INAF - Osservatorio Astrofisico di Catania, Via Santa Sofia 78, I-95123 Catania, Italy; 2 European Southern
Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany; 3 European Space Research and Technology
Centre, Keplerlaan 1, 2200 AG Noordwijk, Netherlands; 4 Space Telescope Science Institute, 3700 San Martin Drive,
Baltimore MD 21218, USA
E-mail contact: katia.biazzo at inaf.it
We report on the accretion properties of low-mass stars in the LH 95 association within the Large Magellanic Cloud(LMC). Using non-contemporaneous wide-band optical and narrow-band Hα photometry obtained with the Hubble
Space Telescope, we identify 245 low-mass pre-main sequence (PMS) candidates showing Hα excess emission above
the 4σ level. We derive their physical parameters, including effective temperatures, luminosities, masses (M⋆ ), ages,
accretion luminosities, and mass accretion rates (Ṁacc ). We identify two different stellar populations: younger than
∼8 Myr with median Ṁacc ∼ 5.4 × 10−8 M⊙ yr−1 (and M⋆ ∼ 0.15 − 1.8 M⊙) and older than ∼8 Myr with medianṀacc ∼ 4.8 × 10−9 M⊙ yr−1 (and M⋆ ∼ 0.6 − 1.2 M⊙). We find that the younger PMS candidates are assembled ingroups around Be stars, while older PMS candidates are uniformly distributed within the region without evidenceof clustering. We find that Ṁacc in LH 95 decreases with time more slowly than what is observed in Galactic starforming regions (SFRs). This agrees with the recent interpretation according to which higher metallicity limits theaccretion process both in rate and duration due to higher radiation pressure. The Ṁacc -M⋆ relationship shows different
behaviour at different ages, becoming progressively steeper at older ages, indicating that the effects of mass and age onṀacc cannot be treated independently. With the aim to identify reliable correlations between mass, age, and Ṁacc , weused for our PMS candidates a multivariate linear regression fit between these parameters. The comparison between
our results with those obtained in other SFRs of our Galaxy and the Magellanic Clouds confirms the importance ofthe metallicity for the study of the Ṁacc evolution in clusters with different environmental conditions.
Accepted by ApJ
https://arxiv.org/pdf/1903.07610

8Rocky super-Earths or waterworlds: the interplay of planet migration, pebble accretionand disc evolution
Bertram Bitsch1 , Sean N. Raymond2 , and Andre Izidoro3
1

Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany; 2 Laboratoire d’Astrophysique de
Bordeaux, CNRS and Université de Bordeaux, Allée Geoffroy St. Hilaire, 33165 Pessac, France; 3 UNESP, Univ.
Estadual Paulista - Grupo de Dinàmica Orbital Planetologia, Guaratinguet, CEP 12.516-410, São Paulo, Brazil
E-mail contact: bitsch at mpia.de
Recent observations have found a valley in the size distribution of close-in super-Earths that is interpreted as a signpost
13that close-in super-Earths are mostly rocky in composition. However, new models predict that planetesimals should
first form at the water ice line such that close-in planets are expected to have a significant water ice component. Here
we investigate the water contents of super-Earths by studying the interplay between pebble accretion, planet migrationand disc evolution. Planets’ compositions are determined by their position relative to different condensation fronts(ice lines) throughout their growth. Migration plays a key role. Assuming that planetesimals start at or exterior to
the water ice line (r > rH2 O ), inward migration causes planets to leave the source region of icy pebbles and therefore
to have lower final water contents than in discs with either outward migration or no migration. The water ice line
itself moves inward as the disc evolves, and delivers water as it sweeps across planets that formed dry. The relative
speed and direction of planet migration and inward drift of the water ice line is thus central in determining planets’water contents. If planet formation starts at the water ice line, this implies that hot close-in super-Earths (r < 0.3au) with water contents of a few percent are a signpost of inward planet migration during the early gas phase. Hot
super-Earths with larger water ice contents on the other hand, experienced outward migration at the water ice line andonly migrated inwards after their formation was complete either because they become too massive to be contained in
the region of outward migration or in chains of resonant planets. Measuring the water ice content of hot super-Earths
may thus constrain their migration history.
Accepted by A&A
http://arxiv.org/pdf/1903.02488

9

The Elusive Majority of Young Moving Groups. I. Young Binaries and Lithium-Rich
Stars in the Solar Neighborhood
Brendan P. Bowler1 , Sasha Hinkley2 , Carl Ziegler3 , Christoph Baranec4 , John E. Gizis5 , Nicholas M.
Law6 , Michael C. Liu7 , Viyang S. Shah1 , Evgenya L. Shkolnik8 , Basmah Riaz9 and Reed Riddle10
1

Department of Astronomy, The University of Texas at Austin, Austin, TX 78712, USA; 2 University of Exeter, Physics
and Astronomy, EX4 4QL Exeter, UK; 3 Dunlap Institute for Astronomy and Astrophysics, University of Toronto,
Toronto, Ontario M5S 3H4, Canada; 4 Institute for Astronomy, University of Hawai‘i at Mānoa, 640 N. A’ohōkū Pl.,Hilo, HI 96720, USA; 5 Department of Physics and Astronomy, University of Delaware, Newark, DE 19716, USA; 6
Department of Physics and Astronomy, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3255,
USA; 7 Institute for Astronomy, University of Hawai‘i at Mānoa, 2680 Woodlawn Drive, Honolulu, HI 96822, USA; 8
School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85281, USA; 9 Universitäts-SternwarteMünchen, Ludwig Maximilians Universität, Scheinerstrasse 1, D-81679 München, Germany; 10 California Institute ofTechnology, 1200 E. California Blvd., Pasadena, CA 91125, USA
E-mail contact: bpbowler at astro.as.utexas.edu
Young stars in the solar neighborhood serve as nearby probes of stellar evolution and represent promising targets
to directly image self-luminous giant planets. We have carried out an all-sky search for late-type (≈ K7–M5) stars
within 100 pc selected primarily on the basis of activity indicators from GALEX and ROSAT. Approximately two
thousand active and potentially young stars are identified, over 600 of which we have followed up with low-resolution
optical spectroscopy and over 1000 with diffraction-limited imaging using Robo-AO at the Palomar 1.5-m telescope.
Strong lithium is present in 58 stars, implying ages spanning ≈10–200 Myr. Most of these lithium-rich stars are newor previously known members of young moving groups including TWA, β Pic, Tuc-Hor, Carina, Columba, Argus,
AB Dor, Upper Centaurus Lupus, and Lower Centaurus Crux; the rest appear to be young low-mass stars without
connections to established kinematic groups. Over 200 close binaries are identified down to 0.′′ 2 — the vast majorityof which are new — and will be valuable for dynamical mass measurements of young stars with continued orbit
monitoring in the future.
Accepted by A&A
http://arxiv.org/pdf/1903.06303

10Realistic On-The-Fly Outcomes of Planetary Collisions: Machine Learning Applied to
Simulations of Giant Impacts
Saverio Cambioni1 , Erik Asphaug1 , Alexandre Emsenhuber1 , Travis S. J. Gabriel2 , Roberto Furfaro3
and Stephen R. Schwartz1
14

1Lunar and Planetary Laboratory, University of Arizona, 1629 E. University Blvd., Tucson, AZ 85721, USA; 2 Schoolof Earth and Space Exploration, Arizona State University, 781 E. Terrace Mall, Tempe, AZ 85287, USA; 3 Systems
and Industrial Engineering Department, University of Arizona, 1127 E. James E. Rogers Way, Tucson, AZ 85721,
USA
E-mail contact: cambioni at lpl.arizona.edu
Planet formation simulations are capable of directly integrating the evolution of hundreds to thousands of planetary
embryos and planetesimals, as they accrete pairwise to become planets. In principle such investigations allow us tobetter understand the final configuration and geochemistry of the terrestrial planets, as well as to place our solar
system in the context of other exosolar systems. These simulations, however, classically prescribe collisions to resultin perfect mergers, but computational advances have begun to allow for more complex outcomes to be implemented.
Here we apply machine learning to a large but sparse database of giant impact studies, streamlining simulations intoa classifier of collision outcomes and a regressor of accretion efficiency. The classifier maps a 4-Dimensional parameter
space (target mass, projectile-to-target mass ratio, impact velocity, impact angle) into the four major collision types:
merger, “graze-and-merge”, “hit-and-run”, and disruption. The definition of the four regimes and their boundary is
fully data-driven; the results do not suffer from any model assumption in the fitting. The classifier maps the structureof the parameter space and provides insights about the outcome regimes. The regressor is a neural network which istrained to closely mimic the functional relationship between the 4-D space of collision parameters, and a real-variable
outcome, the mass of the largest remnant. This work is a prototype of a more complete surrogate model, based on
extended sets of simulations (“big data”), that will quickly and reliably predict specific collision outcomes for use inrealistic N-body dynamical studies of planetary formation.
Accepted by ApJ
http://arxiv.org/pdf/1903.04507

11

Filamentary Accretion Flows in the Infrared Dark Cloud G14.225-0.506 Revealed by
ALMA
Huei-Ru Vivien Chen1 , Qizhou Zhang2 , M. C. H. Wright3 , Gemma Busquet4 , Yuxin Lin5 , Hauyu
Baobab Liu6,7 , F. A. Olguin8 , Patricio Sanhueza9 , Fumitaka Nakamura9 , Aina Palau10 , Satoshi Ohashi11,9 ,Ken’ichi Tatematsu9,12 and Li-Wen Liao8
1

Institute of Astronomy and Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan; 2 Center
for Astrophysics Harvard-Smithsonian, 60 Garden Street, Cambridge, MA 02318, USA; 3 Department of Astronomy,
University of California, Berkeley, CA 94720, USA; 4 Institut de Ciències de l’Espai (ICE, CSIC), Can Magrans, s/n,
E-08193 Cerdanyola del Vallès, Catalonia
and Institut d’Estudis Espacials de Catalunya (IEEC), E-08034, Barcelona, Catalonia; 5 Max-Planck-Institut für
Radioastronomie, D-53121 Bonn, Germany; 6 European Southern Observatory (ESO), Karl-Schwarzschild-Str. 2, D85748 Garching, Germany; 7 Academia Sinica Institute of Astronomy and Astrophysics, P.O. Box 23-141, Taipei 10617,
Taiwan; 8 Institute of Astronomy, National Tsing Hua University, Hsinchu 30013, Taiwan; 9 National Astronomical
Observatory of Japan, National Institutes of Natural Sciences, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan; 10
Instituto de Radioastronomı́a y Astrofı́sica, Universidad Nacional Autónoma de México, P.O. Box 3-72, 58090 Morelia,
Michoacán, México; 11 RIKEN, 2-1, Hirosawa, Wako-shi, Saitama 351-0198, Japan; 12 Department of Astronomical
Science, SOKENDAI (The Graduate University for Advanced Studies), 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
E-mail contact: hchen at phys.nthu.edu.tw
Filaments are ubiquitous structures in molecular clouds and play an important role in the mass assembly of stars. We
present results of dynamical stability analyses for filaments in the infrared dark cloud G14.225−0.506, where a delayed
onset of massive star formation was reported in the two hubs at the convergence of multiple filaments of parsec length.
Full-synthesis imaging is performed with the Atacama Large Millimeter/submillimeter Array (ALMA) to map theN2 H+ (1 − 0) emission in two hub-filament systems with a spatial resolution of ∼ 0.034 pc. Kinematics are derived
from sophisticated spectral fitting algorithm that accounts for line blending, large optical depth, and multiple velocity
components. We identify five velocity coherent filaments and derive their velocity gradients with principal component
analysis. The mass accretion rates along the filaments are up to 10−4 M⊙ yr−1 and are significant enough to affectthe hub dynamics within one free-fall time (∼ 105 yr). The N2 H+ filaments are in equilibrium with virial parameterαvir ∼ 1.2. We compare αvir measured in the N2 H+ filaments, NH3 filaments, 870 µm dense clumps, and 3 mm dense15cores. The decreasing trend in αvir with decreasing spatial scales persists, suggesting an increasingly important roleof gravity at small scales. Meanwhile, αvir also decreases with decreasing non-thermal motions. In combination withthe absence of high-mass protostars and massive cores, our results are consistent with the global hierarchical collapse
scenario.
Accepted by The Astrophysical Journal
http://arxiv.org/pdf/1903.04376

12First interferometric study of enhanced N-fractionation in N2 H+ : the high-mass starforming region IRAS 05358+3543
Laura Colzi1,2 , Francesco Fontani2 , Paola Caselli3, Silvia Leurini4 , Luca Bizzocchi3 and Ginevra Quaia1
1

Universit degli studi di Firenze, Dipartimento di fisica e Astronomia, Via Sansone 1, 50019 Sesto Fiorentino, Italy; 2
INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125, Florence, Italy; 3 Max-Planck-Institt fr extraterrestrische Physik, Giessenbachstrasse 1, D-85748, Garching bei Mnchen, Germany; 4 INAF Osservatorio Astronomico
di Cagliari, Via della Scienza 5, Selargius CA 09047, Italy
E-mail contact: colzi at arcetri.astro.it
Nitrogen (N) fractionation is used as a tool to search for a link between the chemical history of the Solar System andstar-forming regions. A large variation of 14 N/15 N is observed towards different astrophysical sources, and current
chemical models cannot reproduce it. With the advent of high angular resolution radiotelescopes it is now possible tosearch for N-fractionation at core scales. We present IRAM NOEMA observations of the J=1–0 transition of N2 H+ ,15
NNH+ and N15 NH+ towards the high-mass protocluster IRAS 05358+3543. We find 14 N/15 N ratios that spanfrom ∼100 up to ∼220 and these values are lower or equal than those observed with single-dish observations towards
the same source. Since N-fractionation changes across the studied region, this means that it is regulated by local
environmental effects. We find also the possibility, for one of the four cores defined in the protocluster, to have a moreabundant 15 NNH+ with respect to N15 NH+ . This is another indication that current chemical models may be missing
chemical reactions or may not take into account other mechanisms, like photodissociation or grain surface chemistry,that could be important.
Accepted by Monthly Notices of the Royal Astronomical Society Letters
https://arxiv.org/pdf/1903.06567.pdf

13

The ALMA-PILS survey: First detection of nitrous acid (HONO) in the interstellar
medium
A. Coutens1 , N. F. W. Ligterink2 , J.-C. Loison3 , V. Wakelam1 , H. Calcutt4 , M. N. Drozdovskaya2 , J.
K. Jørgensen5 , H. S. P. Müller6, E. F. van Dishoeck7,8 and S. F. Wampfler2
1

Laboratoire d’astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, allée Geoffroy Saint-Hilaire, 33615 Pessac,
France; 2 Center for Space and Habitability (CSH), University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland; 3
Institut des Sciences Moléculaires (ISM), CNRS, Université Bordeaux, 351 cours de la Libération, F-33400, Talence,France; 4 Department of Space, Earth and Environment, Chalmers University of Technology, 41296 Gothenburg,
Sweden; 5 Centre for Star and Planet Formation, Niels Bohr Institute and Natural History Museum of Denmark,
University of Copenhagen, Øster Voldgade 5-7, 1350 Copenhagen K, Denmark; 6 I. Physikalisches Institut, Universitätzu Köln, Zülpicher Str. 77, 50937 Köln, Germany; 7 Leiden Observatory, Leiden University, PO Box 9513, 2300 RA
Leiden, The Netherlands; 8 Max-Planck Institut für Extraterrestrische Physik (MPE), Giessenbachstr. 1, 85748
Garching, Germany
E-mail contact: audrey.coutens at u-bordeaux.fr
Nitrogen oxides are thought to play a significant role as a nitrogen reservoir and to potentially participate in theformation of more complex species. Until now, only NO, N2 O and HNO have been detected in the interstellar medium.
We report the first interstellar detection of nitrous acid (HONO). Twelve lines were identified towards component Bof the low-mass protostellar binary IRAS 16293–2422 with the Atacama Large Millimeter/submillimeter Array, at theposition where NO and N2 O have previously been seen. A local thermodynamic equilibrium model was used to derive
the column density (∼ 9 × 1014 cm−2 in a 0.5” beam) and excitation temperature (∼ 100 K) of this molecule. HNO,
16

NO2 , NO+ , and HNO3 were also searched for in the data, but not detected. We simulated the HONO formation
using an updated version of the chemical code Nautilus and compared the results with the observations. The chemical
model is able to reproduce satisfactorily the HONO, N2 O, and NO2 abundances, but not the NO, HNO, and NH2 OH
abundances. This could be due to some thermal desorption mechanisms being destructive and therefore limiting theamount of HNO and NH2 OH present in the gas phase. Other options are UV photodestruction of these species in icesor missing reactions potentially relevant at protostellar temperatures.
Accepted by A&A Letters
https://arxiv.org/pdf/1903.03378.pdf

14

The dynamical evolution of molecular clouds near the Galactic Centre – III. Tidally–
induced star formation in protocluster clouds
James E. Dale1 , J.M. Diederik Kruijssen2 and S.N. Longmore3
1

Centre for Astrophysics Research, University of Hertfordshire, Hatfield, AL10 9AB, UK; 2 Astronomisches RechenInstitut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstraße 12-14, 69120 Heidelberg, Germany; 3
Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF, UK
E-mail contact: dale.james.e at gmail.com
As part of a series of papers aimed at understanding the evolution of the Milky Way’s Central Molecular Zone
(CMZ), we present hydrodynamical simulations of turbulent molecular clouds orbiting in an accurate model of thegravitational potential extant there. We consider two sets of model clouds differing in the energy content of theirvelocity fields. In the first, self–virialised set, the turbulent kinetic energies are chosen to be close in magnitude to theclouds’ self–gravitational potential energies. Comparison with isolated clouds evolving without an external potential
shows that the self–virialised clouds are unable to withstand the compressive tidal field of the CMZ and rapidly
collapse, forming stars much faster and reaching gas exhaustion after a small fraction of a Galactocentric orbit. In
the second, tidally–virialised, set of simulations, the clouds’ turbulent kinetic energies are in equilibrium with theexternal tidal field. These models are better supported against the field and the stronger turbulence suppresses starformation. Our results strongly support the inference that anomalously low star formation rates in the CMZ are due
primarily to high velocity dispersions in the molecular gas. The clouds follow open, eccentric orbits oscillating in
all three spatial coordinates. We examine the consequences of the orbital dynamics, particularly pericentre passage,by performing companion simulations of clouds on circular orbits. The increased tidal forces at pericentre produce
transient accelerations in star formation rates of at most a factor of 2.7. Our results demonstrate that modelling starformation in galactic centres requires the inclusion of tidal forces.
Accepted by MNRAS
http://arxiv.org/pdf/1903.10617

15

The Mass of Stirring Bodies in the AU Mic Debris Disk Inferred from Resolved Vertical
Structure
Cail Daley1,2 , A. Meredith Hughes1 , Evan S. Carter1 , Kevin Flaherty1,3 , Zachary Lambros1 , Margaret
Pan4 , Hilke Schlichting5,4 , Eugene Chiang6,7 , Mark Wyatt8 , David Wilner9 , Sean Andrews9 and John
Carpenter10
1

Department of Astronomy, Van Vleck Observatory, Wesleyan University, 96 Foss Hill Drive, Middletown, CT 06459,
USA; 2 Department of Astronomy, University of Illinois Urbana-Champaign, Urbana, IL 61801, USA; 3 Departmentof Astronomy and Department of Physics, Williams College, Williamstown, MA 01267, USA; 4 Department of Earth,Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA; 5 Department of Earth, Planetary and Space Sciences, University of California, Los Angeles, CA 90095, USA; 6 Departmentof Astronomy, University of California at Berkeley, Campbell Hall, Berkeley, CA 94720-3411; 7 Department of Earthand Planetary Science, University of California at Berkeley, McCone Hall, Berkeley, CA 94720-4767; 8 Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, United Kingdom; 9 Harvard-Smithsonian
Center for Astrophysics, 60 Garden Street, Cambridge, MA, 02138, USA; 10 Joint ALMA Observatory (JAO), Alonsode Cordova 3107 Vitacura-Santiago de Chile, Chile17E-mail contact: cdaley at wesleyan.edu
The vertical distribution of dust in debris disks is sensitive to the number and size of large planetesimals dynamicallystirring the disk, and is therefore well-suited for constraining the prevalence of otherwise unobservable Uranus and
Neptune analogs. Information regarding stirring bodies has previously been inferred from infrared and optical observations of debris disk vertical structure, but theoretical works predict that the small particles traced by short-wavelength
observations will be ‘puffed up’ by radiation pressure, yielding only upper limits. The large grains that dominate thedisk emission at millimeter wavelengths are much less sensitive to the effects of stellar radiation or stellar winds,
and therefore trace the underlying mass distribution more directly. Here we present ALMA 1.3 mm dust continuum
observations of the debris disk around the nearby M star AU Mic. The 3 au spatial resolution of the observations,combined with the favorable edge-on geometry of the system, allows us to measure the vertical thickness of the disk.
We report a scale height-to-radius aspect ratio of h = 0.031+0.005−0.004 between radii of ∼ 23 au and ∼ 41 au. Comparing
this aspect ratio to a theoretical model of size-dependent velocity distributions in the collisional cascade, we find thatthe perturbing bodies embedded in the local disk must be larger than about 400 km, and the largest perturbing bodymust be smaller than roughly 1.8 M⊙ . These measurements rule out the presence of a gas giant or Neptune analog
near the ∼ 40 au outer edge of the debris ring, but are suggestive of large planetesimals or an Earth-sized planet
stirring the dust distribution.
Accepted by ApJ
https://arxiv.org/pdf/1904.00027.pdf

16

Evidence of interacting elongated filaments in the star-forming site AFGL 5142
Lokesh K. Dewangan1 , Devendra K. Ojha2 , Tapas Baug3 and R. Devaraj4
1

Physical Research Laboratory, Navrangpura, Ahmedabad - 380 009, India; 2 Department of Astronomy and Astrophysics, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400 005, India; 3 Kavli Institute for
Astronomy and Astrophysics, Peking University, 5 Yiheyuan Road, Haidian District, Beijing 100871, P. R. China; 4Instituto Nacional de Astrofı́sica, Óptica y Electrónica, Luis Enrique Erro # 1, Tonantzintla, Puebla, México C.P.
72840
E-mail contact: lokeshd at prl.res.in
To probe the ongoing physical mechanism, we studied a wide-scale environment around AFGL 5142 (area ∼25 pc
× 20 pc) using a multi-wavelength approach. The Herschel column density (N (H2 )) map reveals a massive inverted
Y-like structure (mass ∼6280 M⊙ ), which hosts a pair of elongated filaments (lengths > 10 pc). The Herscheltemperature map depicts the filaments in a temperature range of ∼12.5–13.5 K. These elongated filaments overlap
each other at several places, where N (H2 ) > 4.5 × 1021 cm−2 . The 12 CO and 13 CO line data also show two elongatedcloud components (around −1.5 and −4.5 km s−1 ) toward the inverted Y-like structure, which are connected in thevelocity space. First moment maps of CO confirm the presence of two intertwined filamentary clouds along the lineof sight. These results explain the morphology of the inverted Y-like structure through a combination of two different
filamentary clouds, which are also supported by the distribution of the cold H i gas. Based on the distribution ofyoung stellar objects (YSOs), star formation (SF) activities are investigated toward the inverted Y-like structure. The
northern end of the structure hosts AFGL 5142 and tracers of massive SF, where high surface density of YSOs (i.e.,
5–240 YSOs pc−2 ) reveals strong SF activity. Furthermore, noticeable YSOs are found toward the overlapping zonesof the clouds. All these observational evidences support a scenario of collision/interaction of two elongated filamentary
clouds/flows, which appears to explain SF history in the site AFGL 5142.
Accepted by The Astrophysical Journal
https://arxiv.org/pdf/1903.07099.pdf

17

The protoplanetary disc of HD 163296 as observed by ALMA
P.N. Diep1 , D.T. Hoai1 , N.B. Ngoc1 , P.T. Nhung1 , N.T. Phuong1 , T.T. Thai1 and P. Tuan-Anh1
1

Department of Astrophysics, Vietnam National Space Center, Vietnam Academy of Science and Technology, 18
Hoang Quoc Viet, Hanoi, Vietnam
E-mail contact: zb at shao.ac.cn
18

HD 163296 is one of the few protoplanetary discs displaying rings in the dust component. The present work uses
ALMA observations of the 0.9 mm continuum emission having significantly better spatial resolution (∼8 au) thanpreviously available, providing new insight on the morphology of the dust disc and its double ring structure. The discis shown to be thin and its position angle and inclination with respect to the sky plane are accurately measured as are
the locations and shapes that characterize the observed ring/gap structure. Significant modulation of the intensity ofthe outer ring emission have been revealed and discussed. In addition, earlier ALMA observations of the emission of
three molecular lines, CO (2–1), C18 O (2–1), and DCO+ (3–2), having a resolution of ∼70 au, are used to demonstrate
the Keplerian motion of the gas, found consistent with a central mass of 2.3 solar masses. An upper limit of ∼9% of
the rotation velocity is placed on the in-fall velocity. The beam size is shown to give the dominant contribution to theline widths, accounting for both their absolute values and their dependence on the distance to the central star.
Accepted by Vietnam Journal of Science, Technology and Engineering
http://arxiv.org/pdf/1903.11868

18

Comparing the Properties of GMCs in M33 from Simulations and Observations
C. L. Dobbs1 , E. Rosolowsky2 , A. R. Pettitt3 , J. Braine4 , E. Corbelli5 and J. Sun6
1

School of Physics and Astronomy, University of Exeter, Stocker Road, Exeter, EX4 4QL, UK; 2 Department of
Physics, University of Alberta, Edmonton, AB, Canada; 3 Department of Physics, Faculty of Science, Hokkaido
University, Sapporo 060-0810, Japan; 4 Laboratoire d’Astrophysiquede Bordeaux, Univ. Bordeaux, CNRS , B18N,
allee Geoffroy Saint-Hilaire, 33615 Pessac, France; 5 INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125
Firenze, Italy; 6 Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, OH 43210,
USA
E-mail contact: dobbs at asrto.ex.ac.uk
We compare the properties of clouds in simulated M33 galaxies to those observed in the real M33. We apply a friends offriends algorithm and CPROPS to identify clouds, as well as a pixel by pixel analysis. We obtain very good agreement
between the number of clouds, and maximum mass of clouds. Both are lower than occurs for a Milky Way-typegalaxy and thus are a function of the surface density, size and galactic potential of M33. We reproduce the observed
dependence of molecular cloud properties on radius in the simulations, and find this is due to the variation in gas
surface density with radius. The cloud spectra also show good agreement between the simulations and observations,but the exact slope and shape of the spectra depends on the algorithm used to find clouds, and the range of cloudmasses included when fitting the slope. Properties such as cloud angular momentum, velocity dispersions and virial
relation are also in good agreement between the simulations and observations, but do not necessarily distinguishbetween simulations of M33 and other galaxy simulations. Our results are not strongly dependent on the level of
feedback used here (10 and 20%) although they suggest that 15% feedback efficiency may be optimal. Overall our
results suggest that the molecular cloud properties are primarily dependent on the gas and mass surface density, andless dependent on the localised physics such as the details of stellar feedback, or the numerical code used.
Accepted by MNRAS
https://arxiv.org/pdf/1903.04237

19

Fate of the runner in hit-and-run collisions
Alexandre Emsenhuber1 and Erik Asphaug1
1

Lunar and Planetary Laboratory, University of Arizona, 1629 E. University Blvd. Tucson, AZ 85721, United States

E-mail contact: emsenhuber at lpl.arizona.edu
In similar-sized planetary collisions, a significant part of the impactor often misses the target and continues downrange.
We follow the dynamical evolution of “runners” from giant impacts to determine their ultimate fate. Surprisingly,
runners re-impact their target planets only about half of the time, for realistic collisional and dynamical scenarios.
Otherwise they remain in orbit for tens of millions of years (the limit of our N-body calculations) and longer, or
sometimes collide with a different planet than the first one. When the runner does return to collide again with the19same target planet, its impact velocity is mainly constrained by the outcome of the prior collision. Impact angle andorientation, however, are unconstrained by the prior collision.
Accepted by ApJ
http://arxiv.org/pdf/1903.04508

20

The CARMA-NRO Orion Survey: Statistical Signatures of Feedback in the Orion A
Molecular Cloud
Jesse R. Feddersen1 , Héctor G. Arce1 , Shuo Kong1 , Volker Ossenkopf-Okada2 and John M. Carpenter3
1

Department of Astronomy, Yale University, P.O. Box 208101, New Haven, CT 06520-8101, USA; 2 I. Physikalisches
Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany; 3 Joint ALMA Observatory, Alonso de Cordova
3107 Vitacura, Santiago de Chile, Chile
E-mail contact: jesse.feddersen at yale.edu
We investigate the relationship between turbulence and feedback in the Orion A molecular cloud using maps of 12 CO(1–0), 13 CO (1–0) and C18 O (1–0) from the CARMA-NRO Orion survey. We compare gas statistics with the impact offeedback in different parts of the cloud to test whether feedback changes the structure and kinematics of molecular gas.
We use principal component analysis, the spectral correlation function, and the spatial power spectrum to characterize
the cloud. We quantify the impact of feedback with momentum injection rates of protostellar outflows and wind-blown
shells as well as the surface density of young stars. We find no correlation between shells or outflows and any of the gas
statistics. However, we find a significant anti-correlation between young star surface density and the slope of the 12 CO
spectral correlation function, suggesting that feedback may influence this statistic. While calculating the principal
components, we find peaks in the covariance matrix of our molecular line maps offset by 1–3 km s−1 toward several
regions of the cloud which may be produced by feedback. We compare these results to predictions from molecular
cloud simulations.
Accepted by ApJ
http://arxiv.org/pdf/1903.05104

21

A multi-scale exploration of a massive young stellar object - a transition disk aroundG305.20+0.21?
A. J. Frost1 , R. D. Oudmaijer1 , W. J. de Wit2 and S. L. Lumsden1
1School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK; 2 European Southern Observatory,
Casilla 19001, Santiago 19, Chile

E-mail contact: pyajf at leeds.ac.uk
The rarity of young massive stars combined with the fact that they are often deeply embedded has limited the understanding of their formation. Ground based mid-infrared (IR) interferometry is one way of securing the spatial
resolution required to study massive young stellar objects (MYSOs) and as the spatial-frequency coverage of suchobservations is often incomplete, direct-imaging can be supplementary to such a dataset. By consolidating theseobservations with modelling, the features of a massive protostellar environment can be constrained. This work simultaneously fits the aforementioned observations and a spectral energy distribution (SED) with a 2.5D radiative transfer
model, providing an extensive view of the physical characteristics of the accreting regions of the MYSO G305.20+0.21.
The high-resolution observations were obtained using the Very Large Telescope’s MIDI and VISIR instruments, producing visibilities in the N-band and near-diffraction-limited imaging in the Q-band respectively. A model including
a central protostar with a luminosity of ?5×104 L⊙ surrounded by a low-density bipolar cavity, a flared 1M⊙ disk andan envelope provides a sufficient fit all three types of observation. The need to include a disk in the model implies
that this MYSO follows a scaled-up version of the low-mass star formation process. The weak silicate absorption
feature within the SED requires low-density envelope cavities to be successfully fit and is an atypical characteristic
in comparison to previously studied MYSOs. Additionally, the inner radius of the disk must be three times the dust
sublimation radius to satisfy the MIDI visibilities. The low density, low extinction environment implies the object isa more evolved MYSO and this combined with large inner radius of the disk suggests that it could be an example ofa transitional disk around an MYSO.
20

Accepted by Astronomy & Astrophysics
https://arxiv.org/pdf/1903.04393

22

The role of initial magnetic field structure in the launching of protostellar jets
Isabella A. Gerrard1,2 , Christoph Federrath1 and Rajika Kuruwita1
1

Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611, Australia; 2Monash Centre for Astrophysics, Monash University, Clayton, VIC 3800, Australia
E-mail contact: isabella.gerrard at monash.edu
Magnetic fields are known to play a crucial role in the star formation process, particularly in the formation of jets andoutflows from protostellar discs. The magnetic field structure in star forming regions is not always uniform and ordered,often containing regions of magnetic turbulence. We present grid-based, magneto-hydrodynamical simulations of thecollapse of a 1 M⊙ cloud core, to investigate the influence of complex magnetic field structures on outflow formation,
morphology and efficiency. We compare three cases: a uniform field, a partially turbulent field and a fully turbulent
field, with the same magnetic energy in all three cases. We find that collimated jets are produced in the uniform-field
case, driven by a magneto-centrifugal mechanism. Outflows also form in the partially turbulent case, although weakerand less collimated, with an asymmetric morphology. The outflows launched from the partially turbulent case carry
the same amount of mass as the uniform-field case but at lower speeds, having only have 71% of the momentumof the uniform-field case. In the case of a fully turbulent field, we find no significant outflows at all. Moreover,
the turbulent magnetic field initially reduces the accretion rate and later induces fragmentation of the disc, forming
multiple protostars. We conclude that a uniform poloidal component of the magnetic field is necessary for the drivingof jets.
Accepted by MNRAS
https://arxiv.org/pdf/1903.06705v1.pdf

23

Is it possible to reconcile extragalactic IMF variations with a universal Milky Way IMF?
David Guszejnov1,2 , Philip F. Hopkins2 and Andrew S. Graus1
1

Department of Astronomy, The University of Texas at Austin, Austin, TX 78712, US; 2 TAPIR, MC 350-17,
California Institute of Technology, Pasadena, CA 91125, US
E-mail contact: guszejnov at utexas.edu

One of the most robust observations of the stellar initial mass function (IMF) is its near-universality in the Milky
Way and neighboring galaxies. But recent observations of early-type galaxies can be interpreted to imply a bottomheavy IMF, while others of ultra-faint dwarfs could imply a top-heavy IMF. This would impose powerful constraints
on star formation models. We explore what sort of cloud-scale IMF models could possibly satisfy these constraints.
We utilize simulated galaxies which reproduce (broadly) the observed galaxy properties, while they also provide thedetailed star formation history and properties of each progenitor star-forming cloud. We then consider generic models where the characteristic mass of the IMF is some arbitrary power-law function of progenitor cloud properties,
along with well-known literature IMF models, which scale with Jeans mass, turbulent Bonnor-Ebert mass, temperature, the opacity limit, metallicity, or the protostellar heating mass. We show that no IMF models currently inthe literature - nor any model where the turnover mass is an arbitrary power-law function of a combination of cloud
temperature/density/size/metallicity/velocity dispersion/magnetic field - can reproduce the claimed IMF variation in
ellipticals or dwarfs without severely violating observational constraints in the Milky Way. Specifically, they predict
too much variation in the extreme environments of the Galaxy, compared to that observed. Either the IMF varies ina more complicated manner, or alternative interpretations of the extragalactic observations must be explored.
Accepted by MNRAS
https://arxiv.org/pdf/1903.01533

21

24

Stellar models and isochrones from low-mass to massive stars including pre-main sequence phase with accretion
L. Haemmerlé1, P. Eggenberger1 , S. Ekström1 , C. Georgy1 , G. Meynet1 , A. Postel1 , M. Audard1 , M.
Sørensen1 and T. Fragos1
1Département d’Astronomie, Université de Genève, chemin des Maillettes 51, CH-1290 Versoix, Switzerland

E-mail contact: lionel.haemmerle at unige.ch
Grids of stellar models are useful tools to derive the properties of stellar clusters, in particular young clusters hosting
massive stars, and to provide information on the star formation process in various mass ranges. Because of their shortevolutionary timescale, massive stars end their life while their low-mass siblings are still on the pre-main sequence(pre-MS) phase. Thus the study of young clusters requires consistent consideration of all the phases of stellar evolution.
But despite the large number of grids that are available in the literature, a grid accounting for the evolution fromthe pre-MS accretion phase to the post-MS phase in the whole stellar mass range is still lacking. We build a grid ofstellar models at solar metallicity with masses from 0.8 M⊙ to 120 M⊙ , including pre-MS phase with accretion. We
use the genec code to run stellar models on this mass range. The accretion law is chosen to match the observationsof pre-MS objects on the Hertzsprung-Russell diagram. We describe the evolutionary tracks and isochrones of ourmodels. The grid is connected to previous MS and post-MS grids computed with the same numerical method andphysical assumptions, which provides the widest grid in mass and age to date. Numerical tables of our models andcorresponding isochrones are available online.
Accepted by A&A
https://arxiv.org/pdf/1903.10550

25

Probing the protosolar disk using dust filtering at gaps in the early Solar System
Troels Haugbølle1 , Philipp Weber2 , Daniel P Wielandt3 , Pablo Benı́tez-Llambay2 , Martin Bizzarro4 ,Oliver Gressel2,5 and Martin E. Pessah2
1

Niels Bohr Institute and Centre for Star and Planet Formation, University of Copenhagen, Øster Voldgade 5, DK1350 Copenhagen K, Denmark; 2 Niels Bohr International Academy, Niels Bohr Institute, University of Copenhagen,Blegdamsvej 17, DK-2100 Copenhagen Ø, Denmark; 3 Quadlab and Natural History Museum of Denmark, Universityof Copenhagen, Øster Voldgade 5, DK-1350 Copenhagen K, Denmark; 4 Centre for Star and Planet Formation
and Natural History Museum of Denmark, University of Copenhagen, Øster Voldgade 5, DK-1350 Copenhagen K,
Denmark; 5 Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
E-mail contact: haugboel at nbi.ku.dk
Jupiter and Saturn formed early, before the gas disk dispersed. The presence of gap-opening planets affects the
dynamics of the gas and embedded solids, and halts the inward drift of grains above a certain size. A drift barrier
can explain the absence of calcium-aluminium-rich inclusions (CAIs) in chondrites originating from parent bodies
that accreted in the inner Solar System. Employing an interdisciplinary approach, we use a µ-X-Ray-fluorescencescanner to search for large CAIs and a scanning electron microscope to search for small CAIs in the ordinary chondrite
NWA 5697. We carry out long-term, two-dimensional simulations including gas, dust, and planets to characterize thetransport of grains within the viscous α-disk framework exploring the scenarios of a stand-alone Jupiter, Jupiter andSaturn in situ, or in a 3:2 resonance. In each case, we find a critical grain size above which drift is halted as a functionof the physical conditions in the disk. From the laboratory search we find four CAIs with a largest size of ≈200 µm.
Combining models and data, we provide an estimate for the upper limit of the α-viscosity and the surface density
at the location of Jupiter, using reasonable assumptions about the stellar accretion rate during inward transport of
CAIs, and assuming angular momentum transport to happen exclusively through viscous effects. Moreover, we findthat the compound gap structure in the presence of Saturn in a 3:2 resonance favors inward transport of grains larger
than CAIs currently detected in ordinary chondrites.
Accepted by Astrophysical Journal
https://arxiv.org/pdf/1903.12274.pdf

22

26

A Radiative Heating Model for Chondrule and Chondrite Formation
William Herbst1 and James P. Greenwood1
1

Wesleyan University, Middletown, CT 06457, USA

E-mail contact: wherbst at wesleyan.edu
We propose that chondrules and chondrites formed together during a brief radiative heating event caused by theclose encounter of a small (m to km-scale), primitive planetesimal (SPP) with incandescent lava on the surface of alarge (100 km-scale) differentiated planetesimal (LDP). In our scenario, chondrite lithification occurs by hot isostaticpressing (HIP) simultaneously with chondrule formation, in accordance with the constraints of complementarity andcluster chondrites. Thermal models of LDPs formed near t=0 predict that there will be a very narrow window of time,
coincident with the chondrule formation epoch, during which crusts are thin enough to frequently rupture by impact,
volcanism and/or crustal foundering, releasing hot magma to their surfaces. The heating curves we calculate are more
gradual and symmetric than the “flash heating” characteristic of nebular models, but in agreement with the constraintsof experimental petrology. The SPP itself is a plausible source of the excess O, Na and Si vapor pressure (compared
to a solar nebula environment) that is required by chondrule observations. Laboratory experiments demonstrate that
FeO-poor porphyritic olivine chondrules, the most voluminous type of chondrule, can be made using heating andcooling curves predicted by the “flyby” model. If chondrules are a by-product of chondrite lithification, then theirhigh volume abundance within well-lithified chondritic material is not evidence that they were once widespread within
the Solar System. Relatively rare events, such as the flybys modeled here, could account for their abundance in themeteorite record.
Accepted by Icarus
https://arxiv.org/pdf/1903.12224

27

Origin of Misalignments: Protostellar Jet, Outflow, Circumstellar Disc, and Magnetic
Field
Shingo Hirano1 and Masahiro N. Machida1
1

Kyushu University, Japan

E-mail contact: hirano.shingo.821 at m.kyushu-u.ac.jp
Recent observations uncover various phenomena around the protostar such as misalignment between the outflow andmagnetic field, precession of the jet, and time variability of the ejected clumps, whose origins are under debate. We
perform a three-dimensional resistive magnetohydrodynamics simulation of the protostar formation in a star-forming
core whose rotation axis is tilted at an angle 45◦ with respect to the initial magnetic field, in which the protostar is
resolved with a spatial resolution of 0.01 au. In low-dense outer region, the prestellar core contracts along the magnetic
field lines due to the flux freezing. In high-dense inner region, on the other hand, the magnetic dissipation becomesefficient and weakens the magnetic effects when the gas number density exceeds about 1011 cm−3 . Then, the normal
direction of the flattened disc is aligned with the angular momentum vector. The outflow, jet, and protostellar ejection
are driven from different scales of the circumstellar disc and spout in different directions normal to the warped disc.
These axes do not coincide with the global magnetic field direction and vary with time. This study demonstrates thata couple of misalignment natures reported by observations can be simultaneously reproduced only by assuming thestar-forming core rotating around a different direction from the magnetic field.
Accepted by MNRAS
https://arxiv.org/pdf/1903.05283

28

On the origin of very massive stars around NGC 3603
V. M. Kalari1,2 , J. S. Vink3 , W. de Wit4 , N. J. Bastian5 and R. A. Mendez2
1

Gemini Observatory, Southern Operations Center, c/o AURA, Casilla 603, La Serena, Chile; 2 Departamentode Astronomı́a, Universidad de Chile, Casilla 36-D Santiago, Chile; 3 Armagh Observatory, College Hill, Armagh,
BT61 9DG, UK; 4 European Southern Observatory, Alonso de Cordova 3107, Casilla 19001, Santiago, Chile; 5 Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF, UK
23

E-mail contact: vkalari at gemini.edu
The formation of the most massive stars in the Universe remains an unsolved problem. Are they able to form in
relative isolation in a manner similar to the formation of solar-type stars, or do they necessarily require a clusteredenvironment? In order to shed light on this important question, we study the origin of two very massive stars(VMS): the O2.5If*/WN6 star RFS7 (∼100 M⊙ ), and the O3.5If* star RFS8 (∼70 M⊙ ), found within ≈ 53 and 58 pc
respectively from the Galactic massive young cluster NGC 3603, using Gaia data. RFS7 is found to exhibit motions
resembling a runaway star from NGC 3603. This is now the most massive runaway star candidate known in the
Milky Way. Although RFS8 also appears to move away from the cluster core, it has proper-motion values that appear
inconsistent with being a runaway from NGC 3603 at the 3σ level (but with substantial uncertainties due to distanceand age). Furthermore, no evidence for a bow-shock or a cluster was found surrounding RFS8 from available nearinfrared photometry. In summary, whilst RFS7 is likely a runaway star from NGC 3603, making it the first VMS
runaway in the Milky Way, RFS8 is an extremely young (∼2 Myr) VMS, which might also be a runaway, but thiswould need to be established from future spectroscopic and astrometric observations, as well as precise distances.
If RFS8 were still not meeting the criteria for being a runaway from NGC 3603 from such future data, this would
have important ramifications for current theories of massive star formation, as well as the way the stellar initial massfunction (IMF) is sampled.
Accepted by Astronomy & Astrophysics
https://arxiv.org/pdf/1904.02126

29

Effect of Different Angular Momentum Transport Mechanisms on the Distribution of
Water in Protoplanetary Disks
Anusha Kalyaan1 and Steven J. Desch11School of Earth and Space Exploration, Arizona State University, 550 E Tyler Mall, Tempe, AZ 85281, USA

E-mail contact: akalyaan at asu.edu
The snow line in a protoplanetary disk demarcates regions with H2 O ice from regions with H2 O vapor. Where a planet
forms relative to this location determines how much water and other volatiles it forms with. Giant planet formation
may be triggered at the water snow line if vapor diffuses outward and is cold-trapped beyond the snow line faster thanicy particles can drift inward. In this study we investigate the distribution of water across the snow line, considering
three different radial profiles of the turbulence parameter α(r), corresponding to three different angular momentum
transport mechanisms. We consider the radial transport of water vapor and icy particles by diffusion, advection, anddrift. We show that even for similar values of α, the gradient of α(r) across the snow line significantly changes the snowline location, the sharpness of the volatile gradient across the snow line, and the final water/rock ratio in planetary
bodies. A profile of radially decreasing α, consistent with transport by hydrodynamic instabilities plus magnetic disk
winds, appears consistent with the distribution of water in the solar nebula, with monotonically-increasing radial watercontent and a diverse population of asteroids with different water content. We argue that Σ(r) and water abundance
NH2 O (r)/NH2 (r) are likely a diagnostic of α(r) and thus the mechanism for angular momentum transport in inner
disks.
Accepted by The Astrophysical Journal
https://arxiv.org/pdf/1903.06746

30

Millimeter-wave polarization due to grain alignment by the gas flow in protoplanetary
disks
Akimasa Kataoka1 , Satoshi Okuzumi2 and Ryo Tazaki3
1

National Astronomical Observatory of Japan, Osawa 2-21-1, Mitaka, Tokyo 181-8588, Japan; 2 Department ofEarth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551, Japan;
3
Astronomical Institute, Graduate School of Science, Tohoku University, 6-3 Aramaki, Aoba-ku, Sendai 980-8578,
Japan
E-mail contact: akimasa.kataoka at nao.ac.jp24

Dust grains emit intrinsic polarized emission if they are elongated and aligned in the same direction. The directionof the grain alignment is determined by external forces, such as magnetic fields, radiation, and gas flow against
the dust grains. In this letter, we apply the concept of the grain alignment by gas flow, which is called mechanicalalignment, to the situation of a protoplanetary disk. We assume that grains have a certain helicity, which results in thealignment with the minor axis parallel to the grain velocity against the ambient disk gas and discuss the morphology
of polarization vectors in a protoplanetary disk. We find that the direction of the polarization vectors depends on
the Stokes number, which denotes how well grains are coupled to the gas. If the Stokes number is less than unity,orientation of polarization is in the azimuthal direction since the dust velocity against the gas is in the radial direction.
If the Stokes number is as large as unity, the polarization vectors show a leading spiral pattern since the radial andazimuthal components of the gas velocity against the dust grains are comparable. This suggests that if the observed
polarization vectors show a leading spiral pattern, it would indicate that Stokes number of dust grains is around unity,
which is presumably radially drifting.
Accepted by ApJL
https://arxiv.org/pdf/1903.03529

31

Stellar encounters with giant molecular clouds
Giorgi Kokaia1 , Melvyn B. Davies1
1

Lund Observatory, Department of Astronomy and Theoretical Physics, Lund University, Box 43, SE-221 00 Lund,
SwedenE-mail contact: giorgi at astro.lu.se
Giant molecular clouds (GMCs) are believed to affect the biospheres of planets as their host star passes through them.
We simulate the trajectories of stars and GMCs in the Galaxy and determine how often stars pass through GMCs. We
find a strong decreasing dependence with Galactocentric radius, and with the velocity perpendicular to the Galactic
plane, Vz . The XY -component of the kinematic heating of stars was shown to not affect the GMC hit rate, unlike theZ -dependence (Vz ) implies that stars hit fewer GMCs as they age. GMCs are locations of star formation, therefore
we also determine how often stars pass near supernovae. For the supernovae the decrease with Vz is steeper as how
fast the star passes through the GMC determines the probability of a supernova encounter. We then integrate a setof Sun-like trajectories to see the implications for the Sun. We find that the Sun hits 1.6±1.3 GMCs per Gyr which
results in 1.5±1.1 or (with correction for clustering) 0.8±0.6 supernova closer than 10 pc per Gyr. The different
supernova frequencies are from whether one considers multiple supernova per GMC crossing (few Myr) as separate
events. We then discuss the effect of the GMC hits on the Oort cloud, and the Earth’s climate due to accretion, we
also discuss the records of distant supernova. Finally, we determine Galactic Habitable Zone using our model. For thethin disk we find it to lie between 5.8–8.7 kpc and for the thick disk to lie between 4.5–7.7 kpc.
Accepted by MNRAS
http://arxiv.org/pdf/1903.08026

32

The Core Mass Function in the Infrared Dark Cloud G28.37+0.07
Shuo Kong1
1

Dept. of Astronomy, Yale University, USA

E-mail contact: shuo.kong at yale.edu
In this paper, we analyze the 1.3 mm continuum ALMA data that cover the majority of the infrared dark cloud(IRDC) G28.37+0.07. With a spatial resolution of 0.5” (2500 au at 5 kpc), the continuum image reveals five groupsof dense cores. Each core group has a projected physical scale of about 1 pc, with core masses spanning a dynamic
range of about 100. We use the dendrogram method (astrodendro) and a newly developed graph method (astrograph)to identify individual cores. The core masses are estimated through the millimeter continuum flux, assuming constanttemperature and using an NH3-based gas temperature. We construct core mass functions (CMFs) based on the two
methods and fit a power-law relation dN/d log M ∝ M−α to the CMFs for M > 0.79 M⊙ . In the constant-temperature
scenario, astrograph gives α = 0.80 ± 0.10, while astrodendro gives α = 0.71 ± 0.11, both significantly shallower thanthe Salpeter-type initial mass function with α = 1.35. In the scenario where the NH3 gas temperature is applied to25

cores, astrograph gives α = 1.37 ± 0.06, while astrodendro gives α = 0.87 ± 0.07. Regional CMF slope variation isseen between the core groups. We also compare CMFs in three different environments, including IRDC G28.37+0.07,
IRDC clumps, and G286.21+0.17, using the identical dendrogram method. Results show that IRDCs have smaller αthan the cluster-forming cloud G286.21+0.17.
Accepted by ApJ
https://ui.adsabs.harvard.edu/#abs/2019ApJ...873...31K/abstract

33

Widespread Molecular Outflows in the Infrared Dark Cloud G28.37+0.07: Indicationsof Orthogonal Outflow-Filament Alignment
Shuo Kong1 , Héctor G. Arce1 , Marı́a José Maureira1,2 , Paola Caselli2 , Jonathan C. Tan3,4 and Francesco
Fontani51Dept. of Astronomy, Yale University, USA; 2 Max-Planck-Institute for Extraterrestrial Physics (MPE), Germany;
Dept. of Space, Earth and Environment, Chalmers University of Technology, Sweden; 4 Dept. of Astronomy,
University of Virginia, USA; 5 INAF - Osservatorio Astrofisico di Arcetri, Italy3E-mail contact: shuo.kong at yale.edu
We present ALMA CO(2-1) observations toward a massive infrared dark cloud G28.37+0.07. The ALMA data reveal
numerous molecular (CO) outflows with a wide range of sizes throughout the cloud. Sixty-two 1.3 mm continuum
cores were identified to be driving molecular outflows. We have determined the position angle in the plane-of-skyof 120 CO outflow lobes and studied their distribution. We find that the distribution of the plane-of-sky outflow
position angles peaks at about 100 deg, corresponding to a concentration of outflows with an approximately east-west
direction. For most outflows, we have been able to estimate the plane-of-sky angle between the outflow axis and thefilament that harbors the protostar that powers the outflow. Statistical tests strongly indicate that the distributionof outflow-filament orientations is consistent with most outflow axes being mostly orthogonal to their parent filamentin 3D. Such alignment may result from filament fragmentation or continuous mass transportation from filament to
the embedded protostellar core. The latter is suggested by recent numerical studies with moderately strong magnetic
fields.
Accepted by ApJ
https://arxiv.org/pdf/1903.05273

34

Close companions around young stars
Marina Kounkel1 , Kevin Covey1 , Maxwell Moe2 , Kaitlin M. Kratter2 , Genaro Suárez3 , Keivan G.
Stassun4 , Carlos Román-Zúñiga3, Jesus Hernandez3 , Jinyoung Serena Kim2 , Karla Peña Ramı́rez5 ,Alexandre Roman-Lopes6 , Guy S Stringfellow7 , Karl O Jaehnig4 , Jura Borissova8,9 , Benjamin Tofflemire10 ,Daniel Krolikowski10 , Aaron Rizzuto10 , Adam Kraus10 , Carles Badenes11 , Penélope Longa-Peña5 , Yilen
Gómez Maqueo Chew12 , Rodolfo Barba6 , David L. Nidever13,14 , Cody Brown13 , Nathan De Lee15,4 ,Kaike Pan16 , Dmitry Bizyaev16,17 , Daniel Oravetz16 and Audrey Oravetz16
1

Department of Physics and Astronomy, Western Washington University, 516 High St, Bellingham, WA 98225; 2
Steward Observatory, University of Arizona, 933 N. Cherry Ave., Tucson, AZ 85721, USA; 3 Instituto de Astronomı́a,
Universidad Nacional Autónoma de México, Unidad Académica en Ensenada, Ensenada 22860, Mexico; 4 Departmentof Physics and Astronomy, Vanderbilt University, VU Station 1807, Nashville, TN 37235, USA; 5 Centro de Astronomı́a(CITEVA), Universidad de Antofagasta, Av. Angamos 601, Antofagasta, Chile; 6 Department of Physics & Astronomy,
Universidad de La Serena, Av. Juan Cisternas, 1200 North, La Serena, Chile; 7 Center for Astrophysics and Space
Astronomy, Department of Astrophysical and Planetary Sciences, University of Colorado, 389 UCB, Boulder, CO
80309-0389, USA; 8 Instituto de Fı́sica y Astronomı́a, Universidad de Valparaı́so, Av. Gran Bretaña 1111, Playa Ancha,
Casilla 5030, Chile; 9 Millennium Institute of Astrophysics (MAS), Santiago, Chile; 10 Department of Astronomy, The
University of Texas at Austin, Austin, TX 78712, USA; 11 PITT PACC, Department of Physics and Astronomy,
University of Pittsburgh, Pittsburgh, PA 15260, USA; 12 Instituto de Astronomı́a, Universidad Nacional Autónoma
de México, A.P. 70-264, 04510, Mexico, D.F., Mexico; 13 Department of Physics, Montana State University, P.O.
Box 173840, Bozeman, MT 59717-3840, USA; 14 National Optical Astronomy Observatory, 950 North Cherry Ave,26

Tucson, AZ 85719; 15 Department of Physics, Geology, and Engineering Technology, Northern Kentucky University,
Highland Heights, KY 41099; 16 Apache Point Observatory and New Mexico State University, P.O. Box 59, Sunspot,
NM, 88349-0059, USA; 17 Sternberg Astronomical Institute, Moscow State University, Moscow, Russia
E-mail contact: marina.kounkel at wwu.edu
Multiplicity is a fundamental property that is set early during stellar lifetimes, and it is a stringent probe of the physics
of star formation. The distribution of close companions around young stars is still poorly constrained by observations.
We present an analysis of stellar multiplicity derived from APOGEE-2 spectra obtained in targeted observations of
nearby star-forming regions. This is the largest homogeneously observed sample of high-resolution spectra of youngstars. We developed an autonomous method to identify double lined spectroscopic binaries (SB2s). Out of 5007
sources spanning the mass range of ∼0.05–1.5 M⊙ , we find 399 binaries, including both RV variables and SB2s. The
mass ratio distribution of SB2s is consistent with a uniform for q < 0.95 with an excess of twins with q > 0.95. The
period distribution is consistent with what has been observed in close binaries (< 10 AU) in the evolved populations.
Three systems are found to have q ∼0.1, with a companion located within the brown dwarf desert. There are not
any strong trends in the multiplicity fraction (MF) as a function of cluster age from 1 to 100 Myr. There is a weak
dependence on stellar density, with companions being most numerous at Σ∗ ∼ 30 stars/pc−2 , and decreasing in morediffuse regions. Finally, disk-bearing sources are deficient in SB2s (but not RV variables) by a factor of ∼2; this deficit
is recovered by the systems without disks. This may indicate a quick dispersal of disk material in short-period equalmass systems that is less effective in binaries with lower q.
Accepted by AJ
https://arxiv.org/pdf/1903.10523.pdf

35

Exploring the dimming event of RW Aur A through multi-epoch VLT/X-Shooter spectroscopy
M. Koutoulaki1,2 , S. Facchini3 , C. F. Manara3 , A. Natta1,4 , R. Garcia Lopez1 , R. Fedriani1,2 , A. Carattio Garatti1 , D. Coffey2,1 and T. P. Ray1
1

Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2, Ireland; 2 School of Physics, University
College Dublin, Belfield, Dublin 4, Ireland; 3 European Southern Observatory, Karl-Schwarzschild-Strasse 2, Garching
bei Mnchen, 85748 Germany; 4 INAF/Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
E-mail contact: mariakout at cp.dias.ie

RW Aur A is a classical T Tauri star that has suddenly undergone three major dimming events since 2010. The
reason for these dimming events is still not clear. We aim to understand the dimming properties, examine accretion
variability, and derive the physical properties of the inner disc traced by the CO ro-vibrational emission at nearinfrared wavelengths (2.3 µm). We compared two epochs of X-Shooter observations, during and after the dimming.
We modelled the rarely detected CO bandhead emission in both epochs to examine whether the inner disc properties
had changed. The spectral energy distribution was used to derive the extinction properties of the dimmed spectrum
and compare the infrared excess between the two epochs. Lines tracing accretion were used to derive the mass accretion
rate in both states. The CO originates from a region with physical properties of T=3000 K, NCO =1×1021 cm−2 andvk sin i=113 km/s. The extinction properties of the dimming layer were derived with the effective optical depth ranging
from τef f ∼2.5-1.5 from the UV to the near-IR. The inferred mass accretion rate Ṁacc is ∼ 1.5 × 10−8 M⊙ /yr and∼ 2 × 10−8 M⊙ /yr after and during the dimming respectively. By fitting the spectral energy distribution, additionalemission is observed in the infrared during the dimming event from dust grains with temperatures of 500-700 K. The
physical conditions traced by the CO are similar for both epochs, indicating that the inner gaseous disc properties do
not change during the dimming events. The extinction curve is flatter than that of the interstellar medium, and large
grains of a few hundred microns are thus required. When we correct for the observed extinction, the mass accretion
rate is constant in the two epochs, suggesting that the accretion is stable and therefore does not cause the dimming.
The additional hot emission in the near-IR is located at about 0.5 au from the star and is not consistent with an
occulting body located in the outer regions of the disc. The dimming events could be due to a dust-laden wind, asevere puffing-up of the inner rim, or a perturbation caused by the recent star-disc encounter.
Accepted by Astronomy & Astrophysics
http://arxiv.org/pdf/1903.06423

27

The Origins of Protostellar Core Angular Momenta

36 Aleksandra Kuznetsova1 , Lee Hartmann1 and Fabian Heitsch2
1

University of Michigan, 1085 S. University Ave., Ann Arbor, MI 48109, USA; 2 University of North Carolina - Chapel
Hill, 120 E Cameron Ave, Chapel Hill, NC 27514, USA
E-mail contact: kuza at umich.edu
We present the results of a suite of numerical simulations designed to explore the origin of the angular momenta of
protostellar cores. Using the hydrodynamic grid code Athena with a sink implementation, we follow the formation of
protostellar cores and protostars (sinks) from the subvirial collapse of molecular clouds on larger scales to investigate
the range and relative distribution of core properties. We find that the core angular momenta are relatively unaffectedby large-scale rotation of the parent cloud; instead, we infer that angular momenta are mainly imparted by torques
between neighboring mass concentrations and exhibit a log-normal distribution. Our current simulation results arelimited to size scales ∼ 0.05 pc ( ∼ 104 AU), but serve as first steps toward the ultimate goal of providing initialconditions for higher-resolution studies of core collapse to form protoplanetary disks.
Accepted by ApJ

https://arxiv.org/pdf/1903.09612

Modeling Sulfur Depletion in Interstellar Clouds

37 Jacob C. Laas1 and Paola Caselli1
1

Max-Planck-Institut für extraterrestrische Physik, Garching, DE 85748, Germany

E-mail contact: jclaas at mpe.mpg.de
The elemental depletion of interstellar sulfur from the gas phase has been a recurring challenge for astrochemical
models. Observations show that sulfur remains relatively non-depleted with respect to its cosmic value throughout
the diffuse and translucent stages of an interstellar molecular cloud, but its gas-phase constituents cannot accountfor this cosmic value towards higher-density environments. We have attempted to address this issue by modeling theevolution of an interstellar cloud from its pristine state as a diffuse atomic cloud to a molecular environment of muchhigher density, using a gas/grain astrochem. code and an enhanced sulfur reaction network. A common gas/grain
reaction network has been systematically updated and greatly extended based on previous lit. and models, with afocus on the grain chemistry and processes. A simple model was used to benchmark the resulting network updates,
and the results of the model were compared to typical astronomical observations sourced from the literature. Our
new gas/grain model is able to reproduce the elemental depletion of sulfur, whereby sulfur can be depleted from thegas-phase by two orders of magnitude, and this process may occur under dark cloud conditions if the cloud has achemical age of at least 1 Myrs. The resulting mix of sulfur-bearing species on the grain ranges across all the mostcommon chemical elements (H/C/N/O), not dissimilar to the molecules observed in cometary environments. Notably,
this mixture is not dominated simply by H2 S, unlike all other current astrochem. models. Despite our relatively simple
physical model, most of the known gas-phase S-bearing molecular abundances are accurately reproduced under dense
conditions, however they are not expected to be the primary molecular sinks of sulfur. Our model predicts that mostof the missing sulfur is in the form of organo-sulfur species trapped on grains.
Accepted by A&A
http://arxiv.org/pdf/1903.01232

The ice composition in the disk around V883 Ori revealed by its stellar outburst

38 Jeong-Eun Lee1, Seokho Lee1, Giseon Baek1, Yuri Aikawa2 , Lucas Cieza3 , Sung-Yong Yoon1, Gregory
Herczeg4 , Doug Johnstone5 and Simon Casassus6
1School of Space Research, Kyung Hee University, Yongin-si, Korea; 2 Department of Astronomy, University of Tokyo,
Tokyo, Japan; 3 Facultad de Ingenierı́a y Ciencias, Núcleo de Astronomı́a, Universidad Diego Portales, Santiago, Chile;
4
Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing, China; 5 NRC Herzberg Astronomy andAstrophysics, Victoria, British Columbia, Canada; 6 Departamento de Astronomı́a, Universidad de Chile, Santiago,
Chile
28

E-mail contact: jeongeun.lee at khu.ac.kr
Complex organic molecules (COMs), which are the seeds of prebiotic material and precursors of amino acids andsugars, form in the icy mantles of circumstellar dust grains but cannot be detected remotely unless they are heated
and released to the gas phase. Around solar-mass stars, water and COMs only sublimate in the inner few AU of thecircumstellar disk, making them extremely difficult to spatially resolve and study. Sudden increases in the luminosityof the central star will quickly expand the sublimation front (the so-called snow line) to larger radii, as seen previously
in the FU Ori outburst of the young star V883 Ori. Here, we take advantage of the rapid increase in disk temperatureof V883 Ori to detect and analyse five different COMs — methanol, acetone, acetonitrile, acetaldehyde and methyl
formate — in spatially resolved submillimetre observations. The abundances of COMs in the disk around V883 Ori
are in reasonable agreement with cometary values, suggesting that outbursting young stars can provide a special
opportunity to study the ice composition of material directly related to planet formation.
Accepted by Nature Astronomy
https://arxiv.org/pdf/1809.00353.pdf
https://doi.org/10.1038/s41550-018-0680-0

39

Sulfur chemistry in protoplanetary disks: CS and H2 CS
Romane Le Gal1 , Karin I. Öberg1 , Ryan Loomis2 , Jamila Pegues1 and Jennifer B. Bergner1
1

Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, USA; 2 NRAO, 520 Edgemont
Rd, Charlottesville, VA 22903, USA
E-mail contact: romane.le gal at cfa.harvard.edu

The nature and abundance of sulfur chemistry in protoplanetary disks (PPDs) may impact the sulfur inventory on
young planets and therefore their habitability. PPDs also present an interesting test bed for sulfur chemistry models,since each disk present a diverse set of environments. In this context, we present new sulfur molecule observationsin PPDs, and new S-disk chemistry models. With ALMA we observed the CS 5–4 rotational transition toward five
PPDs (DM Tau, DO Tau, CI Tau, LkCa 15, MWC 480), and the CS 6–5 transition toward three PPDs (LkCa 15,
MWC 480 and V4046 Sgr). Across this sample, CS displays a range of radial distributions, from centrally peaked, togaps and rings. We also present the first detection in PPDs of 13 CS 6–5 (LkCa 15 and MWC 480), C34 S 6–5 (LkCa
15), and H2 CS 817 –716 , 919 –818 and 918 –817 (MWC 480) transitions. Using LTE models to constrain column densities
and excitation temperatures, we find that either 13 C and 34 S are enhanced in CS, or CS is optically thick despite
its relatively low brightness temperature. Additional lines and higher spatial resolution observations are needed to
distinguish between these scenarios. Assuming CS is optically thin, CS column density model predictions reproduce
the observations within a factor of a few for both MWC 480 and LkCa 15. However, the model underpredicts H2 CS
by 1–2 orders of magnitude. Finally, comparing the H2 CS/CS ratio observed toward the MWC 480 disk and towarddifferent ISM sources, we find the closest match with prestellar cores.
Accepted by ApJ
http://arxiv.org/pdf/1903.11105

40

Planetesimal Population Synthesis: Pebble Flux Regulated Planetesimal Formation
Christian T. Lenz1 , Hubert Klahr1 , Tilman Birnstiel2
1

Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg, Germany; 2 University Observatory,
Faculty of Physics, Ludwig-Maximilians-Universität München, Scheinerstr. 1, D-81679 Munich, Germany;
E-mail contact: lenz at mpia.de

We propose an expression for a local planetesimal formation rate proportional to the instantaneous radial pebble flux.
The result — a radial planetesimal distribution — can be used as initial condition to study the formation of planetary
embryos. We follow the idea that one needs particle traps to locally enhance the dust-to-gas ratio sufficiently suchthat particle gas interactions can no longer prevent planetesimal formation on small scales. The location of thesetraps can emerge everywhere in the disk. Their occurrence and lifetime is subject of ongoing research, thus they are
implemented via free parameters. This enables us to study the influence of the disk properties on the formation of29

planetesimals, predicting their time dependent formation rates and location of primary pebble accretion. We showthat large α-values of 0.01 (strong turbulence) prevent the formation of planetesimals in the inner part of the disk,
arguing for lower values of around 0.001 (moderate turbulence), at which planetesimals form quickly at all places
where they are needed for proto-planets. Planetesimals form as soon as dust has grown to pebbles (∼mm to dm)
and the pebble flux reaches a critical value, which is after a few thousand years at 2–3AU and after a few hundred
thousand years at 20–30AU. Planetesimal formation lasts until the pebble supply has decreased below a critical value.
The final spatial planetesimal distribution is steeper compared to the initial dust and gas distribution which helps to
explain the discrepancy between the minimum mass solar nebula and viscous accretion disks.
Accepted by ApJ (874, A36, 2019)http://arxiv.org/pdf/1902.07089

41

Dust settling against hydrodynamic turbulence in protoplanetary discs
Min-Kai Lin1
1

Institute of Astronomy and Astrophysics, Academia Sinica, Taipei 10617, Taiwan

E-mail contact: mklin at asiaa.sinica.edu.tw
Enhancing the local dust-to-gas ratio in protoplanetary discs is a necessary first step to planetesimal formation. In
laminar discs, dust settling is an efficient mechanism to raise the dust-to-gas ratio at the disc midplane. However,turbulence, if present, can stir and lift dust particles, which ultimately hinders planetesimal formation. In thiswork, we study dust settling in protoplanetary discs with hydrodynamic turbulence sustained by the vertical shear
instability. We perform axisymmetric numerical simulations to investigate the effect of turbulence, particle size, andsolid abundance or metallicity on dust settling. We highlight the positive role of drag forces exerted onto the gas by
the dust for settling to overcome the vertical shear instability. In typical disc models we find particles with a Stokes
number ∼ 10−3 can sediment to <∼ 0.02–0.05, where Σd,g are∼10% of the gas scale-height, provided that Σd /Σg >the surface densities in dust and gas, respectively. This coincides with the metallicity condition for small particles
to undergo clumping via the streaming instability. Super-solar metallicities, at least locally, are thus required for aself-consistent picture of planetesimal formation. Our results also imply that dust rings observed in protoplanetary
discs should have smaller scale-heights than dust gaps, provided that the metallicity contrast between rings and gaps
exceed the corresponding contrast in gas density.
Accepted by MNRAS
http://arxiv.org/pdf/1903.03620

42

New powerful outburst of the unusual young star V1318 Cyg S (LkHα 225)
T. Yu. Magakian1 , T.A. Movsessian1 , H.R. Andreasyan1 and M.H. Gevorgyan1
1

Byurakan Astrophysical Observatory NAS Armenia, Byurakan, Aragatsotn prov., 0213, Armenia

E-mail contact: tigmag at sci.am
Aims. Young double star V1318 Cyg, which is associated with a small isolated star-forming region around HAeBe star
BD+40◦ 4124, has very unusual photometric and spectral behavior. We present results of photometric and spectroscopic
observations in the optical range.
Methods. We carried out BVRI CCD photometric observations of V1318 Cyg from 2015 Sept. to 2017 July. For thesame period we acquired medium- and low-resolution spectra. Observations were performed with the 2.6 m telescopeof the Byurakan observatory. We also analyzed the images of this field in IPHAS and other surveys.
Results. We analyze the historical light curve for V1318 Cyg and demonstrate that the southern component, V1318 Cyg S,
after being rather bright in the 1970s (V∼14 mag) started to lower its brightness and in 1990 became practically invisible in the optical. After its reappearance in the second half of the 1990s the star started to become very slowly
brighter. Between 2006 and 2010 V1318 Cyg S started brightening more quickly, and in 2015 had become brighter bymore than five magnitudes in visible light. Since this time V1318 Cyg S has remained at this maximum. Its spectrum
shows little variability and consists of a mixture of emission and absorption lines, which has allowed for estimates of
its spectral type as early Ae, with obvious evidence of matter outow. We derive its current AV ≈ 7.2 and L = 750
30

Lsun thus confirming that V1318 Cyg S should belong to the Herbig Ae stars, making it, along with BD+40◦ 4124 andV1686 Cyg, the third luminous young star in the group. It is very probable that we observe V1318 Cyg S near thepole and that the inclination of its dense and slow (≈ 100 km/s) outow is low.
Conclusions. The unusual variability and other features of V1318 Cyg S make it difficult to classify this star among
known types of eruptive young stars. It could be an extreme, higher-mass example of an EXor, or an object ofintermediate class between EXors and FUors, like V1647 Ori.
Accepted by Astronomy & Astrophysics

43

Connecting substellar and stellar formation. The role of the host star’s metallicity
J. Maldonado1 , E. Villaver2 , C. Eiroa2 , and G. Micela1
1

INAF - Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy; 2 Universidad
Autónoma de Madrid, Dpto. Fı́sica Teórica, Facultad de Ciencias, Campus de Cantoblanco, 28049 Madrid, Spain
E-mail contact: jesus.maldonado at inaf.it

Most of our current understanding of the planet formation mechanism is based on the planet metallicity correlation
derived mostly from solar-type stars harbouring gas-giant planets. To achieve a far more reaching grasp on thesubstellar formation process we aim to analyse in terms of their metallicity a diverse sample of stars (in terms of massand spectral type) covering the whole range of possible outcomes of the planet formation process (from planetesimals
to brown dwarfs and low-mass binaries). Our methodology is based on the use of high-precision stellar parameters
derived by our own group in previous works from high-resolution spectra by using the iron ionisation and equilibrium
conditions. All values are derived in an homogeneous way, except for the M dwarfs where a methodology based on
the use of pseudo equivalent widths of spectral features was used. Our results show that as the mass of the substellar
companion increases the metallicity of the host star tendency is to lower values. The same trend is maintained whenanalysing stars with low-mass stellar companions and a tendency towards a wide range of host star’s metallicity isfound for systems with low mass planets. We also confirm that more massive planets tend to orbit around more massive
stars. The core-accretion formation mechanism for planet formation achieves its maximum efficiency for planets with
masses in the range 0.2 and 2 MJup . Substellar objects with higher masses have higher probabilities of being formed
as stars. Low-mass planets and planetesimals might be formed by core-accretion even around low-metallicity stars.
Accepted by A&A
http://arxiv.org/pdf/1903.01141

44

HH 276, A Collimated Outflow in the Region of FS Tau A/B
T.A. Movsessian1 , T. Yu. Magakian1 and M.H. Gevorgyan1
1

Byurakan Astrophysical Observatory NAS Armenia, Byurakan, Aragatsotn prov., 0213, Armenia

E-mail contact: tigmov at web.am
Results from studies of the extended Herbig-Haro flow HH 276 in the region of FS Tau A/B are presented. Long-slit
and Fabry-Perot spectroscopy were carried out on the 6-m telescope at the Special Astrophysical Observatory of theRussian Academy of Sciences and the 2.6-m telescope at the Byurakan Astrophysical Observatory. A new Herbig-Haroknot HH 276E, located on the axis of the already known outflow HH 276, was discovered. The radial velocities of thisoutflow indicate that the collimated stream is oriented perpendicular to the line of sight. A presumed source of theoutflow, a bright infrared object, has been found. The slit spectrum in the optical range confirms the youth of thisobject and reveals signs of a Herbig-Haro outflow.
Accepted by Astrophysics

45

Revealing signatures of planets migrating in protoplanetary discs with ALMA multiwavelength observations
Pooneh Nazari1 , Richard A. Booth1 , Cathie J. Clarke1 , Giovanni P. Rosotti1,2, Marco Tazzari1 , Attila
Juhasz1 and Farzana Meru3,4
1

Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 0HA, UK; 2 Leiden Observatory,
University of Leiden, P.O. Box 9500, NL-2300 RA, Leiden, the Netherlands; 3 Department of Physics, University of31

Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK; 4 Centre for Exoplanets and Habitability, University of Warwick,
Gibbet Hill Road, Coventry CV4 7AL, UK
E-mail contact: pn297 at cam.ac.uk
Recent observations show that rings and gaps are ubiquitous in protoplanetary discs. These features are often interpreted as being due to the presence of planets; however, the effect of planetary migration on the observed morphology
has not been investigated hitherto. In this work we investigate whether multiwavelength mm/submm observations candetect signatures of planet migration, using 2D dusty hydrodynamic simulations to model the structures generated
by migrating planets and synthesising ALMA continuum observations at 0.85 and 3 mm. We identify three possible
morphologies for a migrating planet: a slowly migrating planet is associated with a single ring outside the planet’s
orbit, a rapidly migrating planet is associated with a single ring inside the planet’s orbit while a planet migrating at
intermediate speed generates one ring on each side of the planet’s orbit. We argue that multiwavelength data candistinguish multiple rings produced by a migrating planet from other scenarios for creating multiple rings, such as
multiple planets or discs with low viscosity. The signature of migration is that the outer ring has a lower spectral
index, due to larger dust grains being trapped there. Of the recent ALMA observations revealing protoplanetary discs
with multiple rings and gaps, we suggest that Elias 24 is the best candidate for a planet migrating in the intermediate
speed regime.
Accepted by MNRAS
http://arxiv.org/pdf/1903.03114

46

The complexity of Orion: an ALMA view III. The explosion impact
L. Pagani1 , E.A. Bergin2 , P.F. Goldsmith3, G. Melnick4 , R. Snell5 and C. Favre6
1

LERMA & UMR8112 du CNRS, Observatoire de Paris, PSL University, Sorbonne Universites, CNRS, F-75014 Paris,
France; 2 Department of Astronomy, University of Michigan, 311 West Hall, 1085 S. University Ave, Ann Arbor,
MI 48109, USA; 3 JPL, Pasadena, California, USA; 4 Harvard-Smithsonian Center for Astrophysics, Cambridge,
Massachusetts, USA; 5 Department of Astronomy, University of Massachusetts, Amherst, MA, 01003, USA; 6 Univ.
Grenoble Alpes, CNRS, IPAG, F-38000 Grenoble, France
E-mail contact: laurent.pagani at obspm.fr
The chemistry of complex organic molecules in interstellar dark clouds is still highly uncertain due in part to the lackof constraining observations. Orion is the closest massive star-forming region, and observations making use of ALMA
allow us to separate the emission regions of various Complex Organic Molecules (COMs) in both velocity and space.
Orion also benefits from an exceptional situation, in that it is the site of a powerful explosive event that occured ∼550
years ago. We show that the closely surrounding Kleinmann-Low region has clearly been influenced by this explosion,
with some molecular species having been pushed away from the densest parts while others have remained in close
proximity. This dynamical segregation reveals the time dependence of the chemistry and, therefore allows us to better
constrain the formation sequence of COMs and other species, including deuterated molecules.
Accepted by A&A Letters
http://aramis.obspm.fr/~pagani/lettre_explosion.pdf

47

A hypothesis for the rapid formation of planets
Susanne Pfalzner1,2 and Michele Bannister3
1

Jülich Supercomputing Centre, Forschungszentrum Jülich, Germany; 2 Max-Planck-Institut für Radioastronomy,
Bonn, Germany; 3 Astrophysics Research Centre, Queen’s University Belfast, UK
E-mail contact: s.pfalzner at fz-juelich.de
The discovery of 1I/Oumuamua confirmed that planetesimals must exist in great numbers in interstellar space. Originally generated during planet formation, they are scattered from their original systems and subsequently drift throughinterstellar space. As a consequence they should seed molecular clouds with at least hundred-metre-scale objects.
We consider how the galactic background density of planetesimals, enriched from successive generations of star andsystem formation, can be incorporated into forming stellar systems. We find that at minimum of the order of 107
32

Oumuamua-sized and larger objects, plausibly including hundred-kilometre-scale objects, should be present in protoplanetary disks. At such initial sizes, the growth process of these seed planetesimals in the initial gas- and dust-richprotoplanetary disks is likely to be substantially accelerated. This could resolve the tension between accretionary
timescales and the observed youth of fully-fledged planetary systems. Our results strongly advocate that the population of interstellar planetesimals should be taken into account in future studies of planet formation. As not only the
Galaxy’s stellar metallicity increased over time but also the density of interstellar objects, we hypothesize that thisenriched seeding enhances planetary formation after the first generation of planetary systems.
Accepted by ApJL
https://arxiv.org/pdf/1903.04451.pdf

48

Multi-epoch Ultraviolet HST Observations of Accreting Low-mass Stars
Connor Robinson1 and Catherine Espaillat1
1

Boston University, 725 Commonwealth Avenue, Boston, MA, 02215, USA

E-mail contact: connorr at bu.edu
Variability is a defining characteristic of young low-mass stars that are still accreting material from their primordial
protoplanetary disk. Here we present the largest HST variability study of Classical T Tauri stars (CTTS) to date.
For 5 of these objects, we obtained a total of 25 spectra with the Space Telescope Imaging Spectrograph (STIS). Massaccretion rates and the fraction of the star covered by accretion columns (i.e., filling factors) were inferred using 1D
NLTE physical models whose parameters were fit within a Bayesian framework. On week long timescales, typicalchanges in the mass accretion rates range up to a factor of ∼ 2, while changes of up to a factor of ∼ 5 are inferred
for the filling factors. In addition to this, we observed a possible accretion burst in the transitional disk system GM
Aur, and an incident we interpret as a chance alignment of an accretion column and the undisturbed photospherealong our line of sight in the full disk system VW Cha. We also measure correlations between mass accretion rateand line luminosities for use as secondary tracers of accretion. We place our objects in context with recent highcadence photometric surveys of low-mass star formation regions and highlight the need for more broad-wavelength,
contemporaneous data to better understand the physical mechanisms behind accretion variability in CTTS.
Accepted by ApJ
https://arxiv.org/pdf/1903.01987

49

How the power spectrum of dust continuum images may hide the presence of a characteristic filament width
Arabindo Roy1,2 , Philippe André1 , Doris Arzoumanian3 , Marc-Antoine Miville-Deschênes1,4,
Vera Könyves1 , Nicola Schneider5 , Stefano Pezzuto6 , Pedro Palmeirm7 , and Jason M. Kirk8
1

Laboratoire d’Astrophysique (AIM), CEA, CNRS, Université Paris-Saclay, Université Paris Diderot, Sorbonne Paris
Cité, 91191 Gif-sur-Yvette, France; 2 Laboratoire d’Astrophysique de Bordeaux, Univ. Bordeaux, CNRS, allée G.
Saint-Hilaire, 33615 Pessac, France; 3 Department of Physics, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi,
464-8602, Japan; 4 Institut d’Astrophysique Spatiale, CNRS, Univ. Paris-Sud, Université Paris-Saclay, Bâtiment 121,
91405 Orsay cedex, France; 5 I. Physik. Institut, University of Cologne, Zülpicher Str. 77, 50937 Koeln, Germany; 6INAF - Istituto di Astrofisica e Planetologia Spaziali, via Fosso del Cavaliere 100, 00133, Roma, Italy ; 7 Instituto de
Astrofı́sica e Ciências do Espaço, Universidade do Porto, Rua das Estrelas, PT4150-762 Porto, Portugal; 8 Universityof Central Lancashire, Preston, Lancashire, PR1 2HE, United Kingdom
E-mail contact: aroy at cita.utoronto.ca and pandre at cea.fr
Context: Herschel observations of interstellar clouds support a paradigm for star formation in which molecular filaments play a central role. One of the foundations of this paradigm is the finding, based on detailed studies of thetransverse column density profiles observed with Herschel, that nearby molecular filaments share a common inner
width of ∼ 0.1 pc. The existence of a characteristic filament width has been recently questioned, however, on the
grounds that it seems inconsistent with the scale-free nature of the power spectrum of interstellar cloud images.
Aims: In an effort to clarify the origin of this apparent discrepancy, we examined the power spectra of the Herschel/SPIRE 250 µm images of the Polaris, Aquila, and Taurus–L1495 clouds in detail and performed a number of33simple numerical experiments by injecting synthetic filaments in both the Herschel images and synthetic backgroundimages.
Methods: We constructed several populations of synthetic filaments of 0.1 pc width with realistic area filling factors(Afil ) and distributions of column density contrasts (δc ). After adding synthetic filaments to the original Herschel images, we re-computed the image power spectra and compared the results with the original, essentially scale-free power
spectra. We used the χ2variance of the residuals between the best power-law fit and the output power spectrum in eachsimulation as a diagnostic of the presence (or absence) of a significant departure from a scale-free power spectrum.
Results: We found that χ2variance depends primarily on the combined parameter δc2 Afil . According to our numerical experiments, a significant departure from a scale-free behavior and thus the presence of a characteristic filament
width become detectable in the power spectrum when δc2 Afil ≥ 0.1 for synthetic filaments with Gaussian profiles andδc2 Afil ≥ 0.4 for synthetic filaments with Plummer-like density profiles. Analysis of the real Herschel 250 µm datasuggests that δc2 Afil is ∼ 0.01 in the case of the Polaris cloud and ∼ 0.016 in the Aquila cloud, significantly below thefiducial detection limit of δc2 Afil ∼ 0.1 in both cases. In both clouds, the observed filament contrasts and area filling
factors are such that the filamentary structure contributes only ∼ 1/5 of the power in the image power spectrum atangular frequencies where an effect of the characteristic filament width is expected.
Conclusions: We conclude that the essentially scale-free power spectra of Herschel images remain consistent with theexistence of a characteristic filament width ∼ 0.1 pc and do not invalidate the conclusions drawn from studies of thefilament profiles.
Accepted by Astronomy and Astrophysics
http://arxiv.org/pdf/1903.12608

50

Planetesimal fragmentation and giant planet formation II: dependencies with planetesimal relative velocities and compositions
I.L. San Sebastián1,2 , O.M. Guilera1,3,4 and M.G. Parisi1,51Facultad de Ciencias Astronómicas y Geofı́sicas, UNLP, Paseo del Bosque S/N, B1900FWA La Plata, Argentina; 2
CONICET, Godoy Cruz 2290, CABA, Argentina; 3 Instituto de Astrofı́sica de La Plata, CCT La Plata, CONICETUNLP, Paseo del Bosque S/N, B1900FWA La Plata, Argentina; 4 Instituto de Astrofı́sica, Pontificia Universidad
Catolica de Chile, Santiago, Chile; 5 Instituto Argentino de Radioastronomı́a, CCT-La Plata, CONICET-CICPBA,
CC N. 5 (1894), Villa Elisa, Argentina
E-mail contact: irina at fcaglp.unlp.edu.ar
Most of planet formation models that incorporate planetesimal fragmentation consider a catastrophic impact energy
threshold for basalts at a constant velocity of 3 km s−1 during all the process of the formation of the planets. However,as planets grow the relative velocities of the surrounding planetesimals increase from velocities of the order of m s−1
to a few km s−1 . In addition, beyond the ice line where giant planets are formed, planetesimals are expected to becomposed roughly by 50% of ices. We aim to study the role of planetesimal fragmentation on giant planet formationconsidering planetesimal catastrophic impact energy threshold as a function of the planetesimal relative velocities andcompositions. We improve our model of planetesimal fragmentation incorporating a functional form of the catastrophic
impact energy threshold with the planetesimal relative velocities and compositions. We also improve in our model theaccretion of small fragments produced by the fragmentation of planetesimals during the collisional cascade considering
specific pebble accretion rates. We find that a more accurate and realistic model for the calculation of the catastrophic
impact energy threshold tends to slow down the formation of massive cores. Only for reduced grain opacity values atthe envelope of the planet, the cross-over mass is achieved before the disk time-scale dissipation. While planetesimal
fragmentation favors the quick formation of massive cores of 5–10 M⊕ the cross-over mass could be inhibited byplanetesimal fragmentation. However, grain opacity reduction or pollution by the accreted planetesimals together
with planetesimal fragmentation could explain the formation of giant planets with low-mass cores.
Accepted by A&A

http://arxiv.org/pdf/1903.12288

34

High Precision Dynamical Masses of Pre-Main Sequence Stars with ALMA and Gaia

51 Patrick D. Sheehan1,2, Ya-Lin Wu3, Josh A. Eisner4 and John Tobin1,2
1National Radio Astronomy Observatory, 520 Edgemont Rd., Charlottesville, VA 22901, USA; 2 Homer L. Dodge
Department of Physics & Astronomy, University of Oklahoma, 440 W. Brooks St., Norman, OK 73021, USA; 3
McDonald Observatory and the Department of Astronomy, University of Texas at Austin, Austin, TX 78712, USA;
4
University of Arizona Department of Astronomy and Steward Observatory, 933 North Cherry Ave., Tucson, AZ
85721, USA
E-mail contact: psheehan at nrao.edu
The Keplerian rotation in protoplanetary disks can be used to robustly measure stellar masses at very high precision
if the source distance is known. We present Atacama Large Millimeter/submillimeter Array (ALMA) observationsof spatially and spectrally resolved 12 CO (2–1) emission towards the disks around 2MASS J16262774–2527247 (thetertiary companion to ROXs 12 at 5100 au), CT Cha, and DH Tau. We employ detailed modeling of the Keplerianrotation profile, coupled with accurate distances from Gaia, to directly measure the stellar masses with ∼2% precision.
We also compare these direct mass measurements with the masses inferred from evolutionary models, determined ina statistically rigorous way. We find that 2MASS J16262774–2527247 has a mass of 0.535+0.006−0.007 M⊙ and CT Cha has
a mass of 0.796+0.015
M,
broadly
consistentwithevolutionarymodels,althoughpotentiallysignificant differences⊙−0.014+0.004
remain. DH Tau has a mass of 0.101−0.003 M⊙ , but it suffers from strong foreground absorption that may affectour mass estimate. The combination of ALMA, Gaia, and codes like pdspy, presented here, can be used to infer
the dynamical masses for large samples of young stars and substellar objects, and place constraints on evolutionarymodels.
Accepted by ApJ
http://arxiv.org/pdf/1903.00032

Extreme Debris Disk Variability — Exploring the Diverse Outcomes of Large Asteroid

52 Impacts During the Era of Terrestrial Planet Formation

Kate Y. L. Su1 , Alan P. Jackson2,3 , András Gáspár1 , George H. Rieke1 , Ruobing Dong4,1 , Johan
Olofsson5,6, G.M. Kennedy7 , Zoë M. Leinhardt8 , Renu Malhotra9 , Michael Hammer1 , Huan Y. A.
Meng1 , W. Rujopakarn10,11,12 , Joseph E. Rodriguez13 , Joshua Pepper14 , D.E. Reichart15 , David James16
and Keivan G. Stassun17,18
1

Steward Observatory, University of Arizona, 933 N Cherry Avenue, Tucson, AZ 85721, USA; 2 Centre for Planetary
Sciences, University of Toronto at Scarborough, 1265 Military Trail, Toronto, ON M1C 1A4, Canada; 3 School ofEarth and Space Exploration, Arizona State University, 781 E. Terrace Mall, Tempe, AZ 85287, USA; 4 Departmentof Physics & Astronomy, University of Victoria, Victoria, BC, V8P 1A1, Canada; 5 Instituto de Fı́sica y Astronomı́a,
Facultad de Ciencias, Universidad de Valparaı́so, Av. Gran Bretaña 1111, Playa Ancha, Valparaı́so, Chile; 6 Núcleo
Milenio Formación Planetaria - NPF, Universidad de Valparaı́so, Av. Gran Bretaña 1111, Valparaı́so, Chile; 7 Department of Physics, University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL, UK; 8 School of Physics, Universityof Bristol, HH Wills Physics Laboratory, Tyndall Avenue, Bristol BS8 1TL, UK; 9 Lunar and Planetary Laboratory,
The University of Arizona, 1629 E University Boulevard, Tucson, AZ 85721, USA; 10 Kavli Institute for the Physics
and Mathematics of the Universe, The University of Tokyo Institutes for Advanced Study, The University of Tokyo,
Kashiwa, Chiba 277-8583, Japan; 11 Department of Physics, Faculty of Science, Chulalongkorn University, 254 Phayathai Road, Pathumwan, Bangkok 10330, Thailand; 12 National Astronomical Research Institute of Thailand (Public
Organization), Don Kaeo, Mae Rim, Chiang Mai 50180, Thailand; 13 Harvard-Smithsonian Center for Astrophysics,
60 Garden St, Cambridge, MA 02138, USA; 14 Department of Physics, Lehigh University, 16 Memorial Drive East,
Bethlehem, PA 18015, USA; 15 University of North Carolina at Chapel Hill; 16 Event Horizon Telescope, Center
for Astrophysics, Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA; 17 Vanderbilt University,
Department of Physics & Astronomy, 6301 Stevenson Center Ln., Nashville, TN 37235, USA; 18 Fisk University,
Department of Physics, 1000 17th Ave. N., Nashville, TN 37208, USA
E-mail contact: ksu at as.arizona.edu
The most dramatic phases of terrestrial planet formation are thought to be oligarchic and chaotic growth, on timescalesof up to 100–200 Myr, when violent impacts occur between large planetesimals of sizes up to proto-planets. Such
35

events are marked by the production of large amounts of debris as has been observed in some exceptionally bright andyoung debris disks (termed extreme debris disks). Here we report five years of Spitzer measurements of such systems
around two young solar-type stars: ID8 and P1121. The short-term (weekly to monthly) and long-term (yearly) disk
variability is consistent with the aftermaths of large impacts involving large asteroid-size bodies. We demonstratethat an impact-produced clump of optically thick dust, under the influence of the dynamical and viewing geometryeffects, can produce short-term modulation in the disk light curves. The long-term disk flux variation is related to thecollisional evolution within the impact-produced fragments once released into a circumstellar orbit. The time-variablebehavior observed in the P1121 system is consistent with a hypervelocity impact prior to 2012 that produced vapor
condensates as the dominant impact product. Two distinct short-term modulations in the ID8 system argue for twoviolent impacts at different times and locations. Its long-term variation is consistent with the collisional evolutionof two different populations of impact-produced debris dominated by either vapor condensates or escaping boulders.
The bright, variable emission from the dust produced in large impacts from extreme debris disks provides a unique
opportunity to study violent events during the era of terrestrial planet formation.
Accepted by AJ
http://arxiv.org/pdf/1903.10627

53

System IMF of the 25 Ori Group from Planetary-Mass Objects to Intermediate/HighMass Stars
Genaro Suárez1 , Juan José Downes2,3 , Carlos Román-Zúñiga1, Miguel Cerviño4,5,6 , César Briceño7 ,Monika G. Petr-Gotzens8 and Katherina Vivas7
1

Instituto de Astronomı́a, Universidad Nacional Autónoma de México, Unidad Académica en Ensenada, Ensenada BC
22860, México; 2 Centro Universitario Regional del Este, Universidad de la República, AP 264, Rocha 27000, Uruguay;
3
Centro de Investigaciones de Astronomı́a, Apartado Postal 264, Mérida, Venezuela; 4 Centro de Astrobiologı́a(CSIC/INTA), 28850 Torrejón de Ardoz, Madrid, Spain; 5 Instituto de Astrofı́sica de Canarias, c/vı́a Láctea s/n, 38205
La Laguna, Tenerife, Spain; 6 Instituto de Astrofı́sica de Andalucı́a (CSIC), 18008, Granada, Spain; 7 Cerro Tololo
Interamerican Observatory, Casilla 603, La Serena, Chile; 8 European Southern Observatory, Karl-Schwarzschild-Str.
2, 85748 Garching bei München, Germany
E-mail contact: gsuarez at astro.unam.mx
The stellar initial mass function (IMF) is an essential input for many astrophysical studies but only in a few cases
it has been determined over the whole cluster mass range, limiting the conclusions about its nature. The 25 Orionis
group (25 Ori) is an excellent laboratory to investigate the IMF across the entire mass range of the population, fromplanetary-mass objects to intermediate/high-mass stars. We combine new deep optical photometry with optical andnear-infrared data from the literature to select 1687 member candidates covering a 1.1◦ radius area in 25 Ori. With thissample we derived the 25 Ori system IMF from 0.012 to 13.1 M⊙ . This system IMF is well described by a two-segment
power-law with Γ = −0.74 ± 0.04 for m < 0.4 M⊙ and Γ = 1.50 ± 0.11 for m ≥ 0.4 M⊙ . It is also well described over
the whole mass range by a tapered power-law function with Γ = 1.10 ± 0.09, mp = 0.31 ± 0.03 and β = 2.11 ± 0.09.
The best lognormal representation of the system IMF has mc = 0.31 ± 0.04 and σ = 0.46 ± 0.05 for m < 1 M⊙ . Thissystem IMF does not present significant variations with the radii. We compared the resultant system IMF as wellas the BD/star ratio of 0.16 ± 0.03 we estimated for 25 Ori with that of other stellar regions with diverse conditions
and found no significant discrepancies. These results support the idea that general star formation mechanisms areprobably not strongly dependent to environmental conditions. We found that the substellar and stellar objects in 25
Ori have similar spatial distributions and confirmed that 25 Ori is a gravitationally unbound stellar association.
Accepted by MNRAS
https://arxiv.org/pdf/1903.05739

54

Gas vs dust sizes of protoplanetary disks: effects of dust evolution
L. Trapman1 , S. Facchini2,3 , M.R. Hogerheijde1,4 , E.F. van Dishoeck1,2 , and S. Bruderer2
1

Leiden Observatory, Leiden University, Niels Bohrweg 2, NL-2333 CA Leiden, The Netherlands; 2 Max-PlanckInstitute für Extraterrestrische Physik, Giessenbachstrasse, D-85748 Garching, Germany; 3 European Southern Ob-

36

servatory, Karl-Schwarzschild-Str. 2, D-85748 Garching bei München, German; 4 Anton Pannekoek Institute for
Astronomy, University of Amsterdam, Science Park 904, 1090 GE Amsterdam, The Netherlands
E-mail contact: trapman at strw.leidenuniv.nl
The extent of the gas in protoplanetary disks is observed to be universally larger than the extent of the dust. This
is often attributed to radial drift and grain growth of the mm grains, but line optical depth produces a similar
observational signature. We investigate in what parts of the disk structure parameter space dust evolution and line
optical depth are the dominant drivers of the observed gas and dust size difference. Using the thermochemical model
DALI with dust evolution included we ran a grid of models aimed at reproducing the observed gas and dust size
dichotomy. The relation between Rdust and dust evolution is non-monotonic and depends on the disk structure. Rgas
is directly related to the radius where the CO column density drops below 1015 cm−2 and CO becomes photodissociated.
Rgas is not affected by dust evolution but scales with the total CO content of the disk. Rgas /Rdust > 4 is a clear signfor dust evolution and radial drift in disks, but these cases are rare in current observations. For disks with a smaller
Rgas /Rdust , identifying dust evolution from Rgas /Rdust requires modelling the disk structure including the total COcontent. To minimize the uncertainties due to observational factors requires FWHMbeam < 1× the characteristic
radius and a peak SNR > 10 on the 12 CO emission moment zero map. For the dust outer radius to enclose most of
the disk mass, it should be defined using a high fraction (90–95%) of the total flux. For the gas, any radius enclosing> 60% of the 12 CO flux will contain most of the disk mass. To distinguish radial drift and grain growth from line
optical depth effects based on size ratios requires disks to be observed at high enough angular resolution and the disk
structure should to be modelled to account for the total CO content of the disk.
Accepted by A&A
http://arxiv.org/pdf/1903.06190

Molecular Cloud Cores in the Galactic Center 50 km s−1 Molecular Cloud

55 Kenta Uehara1 , Masato Tsuboi1,2, Yoshimi Kitamura2 , Ryosuke Miyawaki3 and Atsushi Miyazaki4
1

Department of Astronomy, The University of Tokyo, Bunkyo, Tokyo 113-0033, Japan; 2 Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa
252-5210, Japan; 3 College of Arts and Sciences, J.F. Oberlin University, Machida, Tokyo 194-0294, Japan; 4 Japan
Space Forum, Kandasurugadai, Chiyoda-ku, Tokyo, 101-0062, Japan
E-mail contact: uehara at vsop.isas.jaxa.jp
The Galactic Center 50 km s−1 Molecular Cloud (50MC) is the most remarkable molecular cloud in the Sagittarius
A region. This cloud is a candidate for the massive star formation induced by cloud-cloud collision (CCC) with acollision velocity of ∼30 km s−1 that is estimated from the velocity dispersion. We observed the whole of the 50MC
with a high angular resolution (∼2.′′ 0× 1.′′ 4) in ALMA cycle 1 in the H13 CO+ J=1–0 and C34 S J=2–1 emission lines.
We identified 241 and 129 bound cores with a virial parameter of less than 2, which are thought to be gravitationallybound, in the H13 CO+ and C34 S maps using the clumpfind algorithm, respectively. In the CCC region, the boundH13 CO+ and C34 S cores are 119 and 82, whose masses are 68 % and 76 % of those in the whole 50MC, respectively.
The distribution of the core number and column densities in the CCC are biased to larger densities than those in the
non-CCC region. The distributions indicate that the CCC compresses the molecular gas and increases the number ofthe dense bound cores. Additionally, the massive bound cores with masses of > 3000 M⊙ exist only in the CCC region,
although the slope of the core mass function (CMF) in the CCC region is not different from that in the non-CCC
region. We conclude that the compression by the CCC efficiently formed massive bound cores even if the slope of the
CMF is not changed so much by the CCC.
Accepted by Astrophysics of Galaxies

http://arxiv.org/pdf/1903.01759

Multi-line Herschel/HIFI observations of water reveal infall motions and chemical seg-

56 regation around high-mass protostars

Floris van der Tak1 , Russ Shipman 1 , Thierry Jacq2 , Fabrice Herpin2 , Jonathan Braine2 and Friedrich
Wyrowski3

37

1

SRON / U Groningen, The Netherlands; 2 Université de Bordeaux, France; 3 Max-Planck-Institut für Radioastronomie, Bonn, Germany
E-mail contact: vdtak at sron.nl
The physical conditions during high-mass star formation are poorly understood. Outflow and infall motions havebeen detected around massive protostellar objects, but their dependence on mass, luminosity, and age is unclear. In
addition, physical conditions and molecular abundances are often estimated using simple assumptions such as sphericalshape and chemical homogeneity, which may limit the accuracy of the results. We aim to characterize the dust andgas distribution and kinematics of the envelopes of high-mass protostars. In particular, we search for infall motions,abundance variations, and deviations from spherical symmetry, using Herschel data from the WISH program.
We used HIFI maps of the 987 GHz H2 O 202 –111 emission to measure the sizes and shapes of 19 high-mass protostellar
envelopes. To identify infall, we used HIFI spectra of the optically thin C18 O 9–8 and H18
2 O 111 –000 lines. The high-J
C18 O line traces the warm central material and redshifted H18O1–0
absorption
indicates
material falling onto the
1100
2warm core. We probe small-scale chemical differentiation by comparing H2 O 752 and 987 GHz spectra with those of
H18
2 O.
Our measured radii of the central part of the H2 O 202 –111 emission are 30-40% larger than the predictions fromspherical envelope models, and axis ratios are <2, which we consider good agreement. For 11 of the 19 sources, we
18find a significant redshift of the H18
2 O 111 –000 line relative to C O 9–8. The inferred infall velocities are 0.6–3.2−1−5
km s , and estimated mass inflow rates range from 7×10 to 2×10−2 M⊙ /yr. The highest mass inflow rates seemto occur toward the sources with the highest masses, and possibly the youngest ages. The other sources show either
18
expanding motions or H18
2 O lines in emission. The H2 O 111 –000 line profiles are remarkably similar to the differences
between the H2 O 202 –111 and 211 –202 profiles, suggesting that the H18
2 O line and the H2 O 202 –111 absorption originate
just inside the radius where water evaporates from grains, typically 1000–5000 au from the center. In some sources,18
the H18
2 O line is detectable in the outflow, where no C O emission is seen.
18
Together, the H18
2 O absorption and C O emission profiles show that the water abundance around high-mass protostars
has at least three levels: low in the cool outer envelope, high within the 100 K radius, and very high in the outflowinggas. Thus, despite the small regions, the combination of lines presented in this work reveals systematic inflows andchemical information about the outflows.

Accepted by A&A
http://arxiv.org/pdf/1903.11305

57

The ALMA-PILS survey: Gas dynamics in IRAS 16293-2422 and the connection between its two protostars
M.H.D. van der Wiel1,2 , S.K. Jacobsen2 , J.K. Jørgensen2 , T.L. Bourke3 , L.E. Kristensen2 , P. Bjerkeli4,2 ,N.M. Murillo5 , H. Calcutt2 , H.S.P. Müller6, A. Coutens7 , M.N. Drozdovskaya8 , C. Favre9 and S.F. Wampfler8
1

ASTRON Netherlands Institute for Radio Astronomy, Dwingeloo, NL; 2 Centre for Star and Planet Formation,
University of Copenhagen, DK; 3 SKA Organisation, Jodrell Bank Observatory, UK; 4 Department of Space, Earthand Environment, Chalmers University of Technology, Onsala, SE; 5 Leiden Observatory, Leiden University, NL; 6
I. Physikalisches Institut, Universität zu Köln, DE; 7 Laboratoire d’Astrophysique de Bordeaux, Univ. Bordeaux, FR;
8
Center for Space and Habitability, Universität Bern, CH; 9 INAF-Osservatorio Astrofisico di Arcetri, Florence, IT
E-mail contact: mhd at vanderwiel.org
The majority of stars form in binary or higher order systems. The evolution of each protostar in a multiple system
may start at different times and may progress differently. The Class 0 protostellar system IRAS 16293−2422 contains
two protostars, “A” and “B”, separated by ∼600 au and embedded in a single, 104 au scale envelope. Their relative
evolutionary stages have been debated. We aim to study the relation and interplay between the two protostars A
and B at spatial scales of 60 au up to ∼103 au. We selected molecular gas line transitions of the species CO, H2 CO,
HCN, CS, SiO, and CCH from the ALMA-PILS spectral imaging survey (329–363 GHz) and used them as tracers ofkinematics, density, and temperature in the IRAS 16293−2422 system. The angular resolution of the PILS data set
allows us to study these quantities at a resolution of 0.5 arcsec (60 au at the distance of the source). Line-of-sightvelocity maps of both optically thick and optically thin molecular lines reveal: (i) new manifestations of previously
known outflows emanating from protostar A; (ii) a kinematically quiescent bridge of dust and gas spanning between
38the two protostars, with an inferred density between 4 × 104 and ∼3 × 107 cm−3 ; and (iii) a separate, straight filamentseemingly connected to protostar B seen only in CCH, with a flat kinematic signature. Signs of various outflows,
all emanating from source A, are evidence of high-density and warmer gas; none of them coincide spatially andkinematically with the bridge. We hypothesize that the bridge arc is a remnant of filamentary substructure in the
protostellar envelope material from which protostellar sources A and B have formed. One particular morphologicalstructure appears to be due to outflowing gas impacting the quiescent bridge material. The continuing lack of clear
outflow signatures unambiguously associated to protostar B and the vertically extended shape derived for its disk-likestructure lead us to conclude that source B may be in an earlier evolutionary stage than source A.
Accepted by A&A
https://arxiv.org/pdf/1903.12606

58

Fates of hydrous materials during planetesimal collisions
Shigeru Wakita1 and Hidenori Genda1
1

Earth-Life Science Institute, Tokyo Institute of Technology 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550, Japan

E-mail contact: shigeru at elsi.jp
Hydrous minerals are found on the surfaces of asteroids, but their origin is not clear. If their origin is endogenic,
the hydrous minerals that were formed in the inner part of a planetesimal (or parent body) should come out on to
the surface without dehydration. If their origin is exogenic, the source of hydrous minerals accreting onto asteroids isneeded. Collisions in the asteroid belt would be related to both origins because collisions excavate the surface and eject
the materials. However, the fate of hydrous minerals in large planetesimals during the collisional process has not been
well investigated. Here, we explore planetesimal collisions by using the iSALE-2D code, and investigate the effect of an
impact for the target planetesimal containing hydrous minerals. Our numerical results for the fiducial case (5 km s−1of the impact velocity) show that hydrous minerals are slightly heated during the collisions. This moderate heating
indicates that they can avoid the dehydration reaction and keep their original composition. Some hydrous minerals
have larger velocity than the escape velocity of the collision system. This means that hydrous minerals can escapefrom the planetesimal and support the theory of exogenic origin for the hydrous minerals on asteroids. Meanwhile, thevelocity of other hydrous minerals is smaller than the escape velocity of the system. This also indicates the possibilityof an endogenic origin for the hydrous minerals on asteroids. Our results suggest that hydrous minerals on asteroids
can be provided by planetesimal collisions.
Accepted by Icarus
http://arxiv.org/pdf/1903.04675

59

New Near-Infrared Imaging and Spectroscopy of NGC 2071-IR
D. M. Walther1 and T. R. Geballe1
1Gemini Observatory

E-mail contact: tgeballe at gemini.edu
We present high resolution images of NGC 2071-IR in the J, H, and K bands and in the emission at 2.12 ?m of the
v=1?0 S(1) line of molecular hydrogen. We also present moderate resolution K-band spectra of two young stellar
objects, IRS 1 and IRS 3, within NGC 2071-IR, that are candidates sources of one or more of the outflows observed in
the region. Two of the eight originally identified infrared point sources in NGC 2071-IR are binaries, and we identifiy
two new sources, one coincident with the radio source VLA-1 and highly reddened. The H2 Q(3)/S(1) line intensity
ratios at IRS 1 and IRS 3 yield high and very high extinctions, respectively, to them, as is implied by their near-infraredcolors and K-band continuum slopes. The spectra also reveal the presence of hot, dense circumstellar molecular gas
in each, suggesting that both are strong candidates for having energetic molecular outflows. We agree with a previous
suggestion that IRS 1 is the likely source of an E-W-oriented outflow and conclude that this outflow is probably largelyout of the plane of the sky. We also conclude that if IRS 3 is the source of the large scale NE-SW outflow, as has
been previously suggested, its jet/wind must precess in order to explain the angular width of that outflow. We discuss
the natures of the point sources and their probable contributions, if any, to the complex morphology of the H2 line
emission.
39

Accepted by The Astrophysical Journal
https://arxiv.org/pdf/1903.03583

60

Sheets, filaments and clumps - high resolution simulations of how the thermal instability
can form molecular clouds
C.J. Wareing1 , S.A.E.G. Falle2 and J.M. Pittard1
1

School of Physics and Astronomy, University of Leeds, Leeds, UK, LS2 9JT; 2 School of Mathematics, University ofLeeds, Leeds, UK, LS2 9JT
E-mail contact: C.J.Wareing at leeds.ac.uk
This paper describes 3D simulations of the formation of collapsing cold clumps via thermal instability inside a larger
cloud complex. The initial condition was a diffuse atomic, stationary, thermally unstable, 200 pc diameter spherical
cloud in pressure equilibrium with low density surroundings. This was seeded with 10% density perturbations at thefinest initial grid level (0.29 pc) around nH =1.1 cm−3 and evolved with self-gravity included. No magnetic field was
imposed. Resimulations at a higher resolution of a region extracted from this simulation (down to 0.039 pc), showthat the thermal instability forms sheets, then filaments and finally clumps. The width of the filaments increases overtime, in one particular case from 0.26 to 0.56 pc. Thereafter clumps with sizes of around 5 pc grow at the intersectionsof filaments. 21 distinct clumps, with properties similar to those observed in molecular clouds, are found by using the
FellWalker algorithm to find minima in the gravitational potential. Not all of these are gravitationally bound, but theconvergent nature of the flow and increasing central density suggest they are likely to form stars. Further simulationof the most massive clump shows the gravitational collapse to a density > 106 cm−3 . These results provide realistic
initial conditions that can be used to study feedback in individual clumps, interacting clumps and the entire molecular
cloud complex.
Accepted by MNRAS
https://arxiv.org/pdf/1812.09051v2

61

The Gaia-ESO Survey: Asymmetric expansion of the Lagoon Nebula cluster NGC 6530
from GES and Gaia DR2
Nicholas J. Wright1 , R.D. Jeffries1 , R.J. Jackson1 , A. Bayo2,3 , R. Bonito4 , F. Damiani4 , V. Kalari5 , A.C.
Lanzafame6 , E. Pancino7,8 , R.J. Parker9 , L. Prisinzano4 , S. Randich7 , J.S. Vink10 , E.J. Alfaro11 , M.
Bergemann12 , E. Franciosini7 , G. Gilmore13 , A. Gonneau13 , A. Hourihane13 , P. Jofré14 , S.E. Koposov13 ,J. Lewis13 , L. Magrini7 , G. Micela4 , L. Morbidelli7, G.G. Sacco7 , C.C. Worley13 and S. Zaggia15
1

Astrophysics Group, Keele University, Keele, ST5 5BG, UK; 2 Instituto de Fı́sica y Astronomiı́a, Universidad de
Valparaı́so, Chile; 3 Núcleo Milenio Formación Planetaria - NPF, Universidad de Valparaı́so, Av. Gran Bretaña1111, Valparaı́so, Chile; 4 INAF - Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134, Palermo,
Italy; 5 Departamento de Astronomı́a, Universidad de Chile, Casilla 36-D, Santiago, Chile; 6 Dipartimento di Fisica e
Astronomia, Sezione Astrofisica, Universitá di Catania, via S. Sofia 78, 95123, Catania, Italy; 7 INAF - Osservatorio
Astrofisico di Arcetri, Largo E. Fermi 5, 50125, Florence, Italy; 8 Space Science Data Center - Agenzia Spaziale
Italiana, via del Politecnico, s.n.c., I-00133, Roma, Italy; 9 Department of Physics & Astronomy, University of Sheffield,
Sheffield, S3 7RH, UK; 10 Armagh Observatory, College Hill, Armagh, BT61 9DG, Northern Ireland, UK; 11 Institutode Astrofı́sica de Andalucı́a (CSIC), Glorieta de la Astronomı́a s/n, Granada 18008, Spain; 12 Max-Planck Institutfür Astronomie, Königstuhl 17, 69117 Heidelberg, Germany; 13 Institute of Astronomy, University of Cambridge,
Madingley Road, Cambridge CB3 0HA, United Kingdom; 14 Núcleo de Astronomı́a, Universidad Diego Portales, Av.
Ejercito 441, Santiago, Chile; 15 INAF - Osservatorio Astronomico di Padova, Vicolo della Osservatorio 5, 35122
Padova, Italy
E-mail contact: nick.nwright at gmail.com
The combination of precise radial velocities from multi-object spectroscopy and highly accurate proper motions from
Gaia DR2 opens up the possibility for detailed 3D kinematic studies of young star forming regions and clusters. Here,
we perform such an analysis by combining Gaia-ESO Survey spectroscopy with Gaia astrometry for ∼900 members of−1
the Lagoon Nebula cluster, NGC 6530. We measure the 3D velocity dispersion of the region to be 5.35+0.39,−0.34 km s
40

which is large enough to suggest the region is gravitationally unbound. The velocity ellipsoid is anisotropic, implyingthat the region is not sufficiently dynamically evolved to achieve isotropy, though the central part of NGC 6530 does
exhibit velocity isotropy that suggests sufficient mixing has occurred in this denser part. We find strong evidence thatthe stellar population is expanding, though this is preferentially occurring in the declination direction and there is very
little evidence for expansion in the right ascension direction. This argues against a simple radial expansion pattern, as
predicted by models of residual gas expulsion. We discuss these findings in the context of cluster formation, evolution
and disruption theories.
Accepted by MNRAS
http://arxiv.org/pdf/1903.12176

62

Parallaxes for star forming regions in the inner Perseus spiral arm
Bo Zhang1 , Mark J. Reid2 , Lian Zhang1 , Yuanwei Wu3,4 , Bo Hu5 , Nobuyuki Sakai4 , Karl M. Menten6 ,Xingwu Zheng5 , Andreas Brunthaler6 , Thomas M. Dame7 and Ye Xu8
1Shanghai Astronomical Observatory, Chinese Academy of Sciences 80 Nandan Road, Shanghai 200030, China;
Center for Astrophysics — Harvard & Smithsonian 60 Garden Street, Cambridge, MA 02138, USA; 3 National
Time Service Center, Chinese Academy of Sciences Xi’an 710600, China; 4 Mizusawa VLBI Observatory, National
Astronomical Observatory of Japan Mitaka, Tokyo 181-8588, Japan; 5 School of Astronomy and Space Science, Nanjing
University 22 Hankou Road, Nanjing 210093, China; 6 Max-Plank-Institut für Radioastronomie Auf dem Hügel 69,
53121 Bonn, Germany; 7 Harvard-Smithsonian Center for Astrophysics 60 Garden Street, Cambridge, MA 02138,
USA; 8 Purple Mountain Observatory, Chinese Academy of Sciences Nanjing 210008, China

2E-mail contact: zb at shao.ac.cn
We report trigonometric parallax and proper motion measurements of 6.7-GHz CH3 OH and 22-GHz H2 O masers ineight high-mass star-forming regions (HMSFRs) based on VLBA observations as part of the BeSSeL Survey. The
distances of these HMSFRs combined with their Galactic coordinates, radial velocities, and proper motions, allow us◦
to assign them to a segment of the Perseus arm with <∼70 . These HMSFRs are clustered in Galactic longitude from◦◦∼30 to ∼50 , neighboring a dirth of such sources between longitudes ∼50◦ to ∼90◦ .
Accepted by AJ
http://arxiv.org/pdf/1903.11594

63

Dynamics of a Massive Binary at BirthYichen Zhang1 , Jonathan C. Tan2,3 , Kei E. I. Tanaka4,5 , James M. De Buizer6 , Mengyao Liu3 , MariaT. Beltrán7 , Kaitlin Kratter8 , Diego Mardones9 and Guido Garay9
1
Star and Planet Formation Laboratory, RIKEN Cluster for Pioneering Research, Hirosawa 2-1, Wako-shi, Saitama
351-0198, Japan; 2 Department of Space, Earth & Environment, Chalmers University of Technology, SE-412 96
Gothenburg, Sweden; 3 Department of Astronomy, University of Virginia, Charlottesville, VA 22904-4325, USA; 4
Department of Earth and Space Science, Osaka University, Toyonaka, Osaka 560-0043, Japan; 5 Chile Observatory,
National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588, Japan; 6 SOFIA-USRA, NASA Ames ResearchCenter, MS 232-12, Moffett Field, CA 94035, USA; 7 INAF Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5,50125 Firenze, Italy; 8 Department of Astronomy and Steward Observatory, University of Arizona, 933 N Cherry Ave,
Tucson, AZ, 85721, USA; 9 Departamento de Astronomı́a, Universidad de Chile, Casilla 36-D, Santiago, Chile

E-mail contact: yczhang.astro at gmail.com
Almost all massive stars have bound stellar companions, existing in binaries or higher-order multiples. While binarity
is theorized to be an essential feature of how massive stars form, essentially all information about such properties
is derived from observations of already formed stars, whose orbital properties may have evolved since birth. Little
is known about binarity during formation stages. Here we report high angular resolution observations of 1.3 mm
continuum and H30α recombination line emission, which reveal a massive protobinary with apparent separation of
180 au at the center of the massive star-forming region IRAS07299-1651. From the line-of-sight velocity difference of
9.5 km s−1 of the two protostars, the binary is estimated to have a minimum total mass of 18 solar masses, consistent
with several other metrics, and maximum period of 570 years, assuming a circular orbit. The H30α line from the41

primary protostar shows kinematics consistent with rotation along a ring of radius of 12 au. The observations indicatethat disk fragmentation at several hundred au may have formed the binary, and much smaller disks are feeding theindividual protostars.
Accepted by Nature Astronomy
https://arxiv.org/pdf/1903.07532

64

Physical Properties of Large-Scale Galactic Filaments
Catherine Zucker1 , Cara Battersby2 and Alyssa Goodman1
1

Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138; 2 Department of Physics, University of Connecticut, Storrs, CT 06269, USA
E-mail contact: catherine.zucker at cfa.harvard.edu
The characterization of our Galaxy’s longest filamentary gas features has been the subject of several studies in recent
years, producing not only a sizeable sample of large-scale filaments, but also confusion as to whether all these features(e.g. “Bones”, “Giant Molecular Filaments”) are the same. They are not. We undertake the first standardized analysisof the physical properties (H2 column densities, dust temperatures, morphologies, radial column density profiles) andkinematics of large-scale filaments in the literature. We expand and improve upon prior analyses by using the samedata sets, techniques, and spiral arm models to disentangle the filaments’ inherent properties from selection criteria
and methodology. Our results suggest that the myriad filament finding techniques are uncovering different physicalstructures, with length (11−269 pc), width (1−40 pc), mass (3×103 M⊙ −1.1×106 M⊙ ), aspect ratio (3:1-117:1), andhigh column density fraction (0.2-100%) varying by over an order of magnitude across the sample of 45 filaments. We
develop a radial profile fitting code, RadFil, which is publicly available. We also perform a position-position-velocity(p-p-v ) analysis on a subsample and find that while 60-70% lie spatially in the plane of the Galaxy, only 30-45%
concurrently exhibit spatial and kinematic proximity to spiral arms. In a parameter space defined by aspect ratio,
dust temperature, and column density, we broadly distinguish three filament categories, which could indicate different
formation mechanisms or histories. Highly elongated “Bone-like” filaments show the most potential for tracing grossspiral structure (e.g. arms, spurs), while other categories could be large concentrations of molecular gas (GMCs, corecomplexes).
Accepted by ApJ
https://arxiv.org/pdf/1712.09655

65

Mapping Distances Across the Perseus Molecular Cloud Using CO Observations, Stellar
Photometry, and Gaia DR2 Parallax Measurements
Catherine Zucker1 , Edward Schlafly2 , Joshua Speagle1 , Gregory Green3 , Stephen Portillo4 , Douglas
Finkbeiner1 and Alyssa Goodman1
1

Harvard-Smithsonian Center for Astrophysics; 2 Lawrence Berkeley National Laboratory; 3 Kavli Institute forParticle Astrophysics and Cosmology; 4 DIRAC Institute, Department of Astronomy, University of Washington
E-mail contact: catherine.zucker at cfa.harvard.edu
We present a new technique to determine distances to major star-forming regions across the Perseus Molecular Cloud,using a combination of stellar photometry, astrometric data, and 12 CO spectral-line maps. Incorporating the Gaia
DR2 parallax measurements when available, we start by inferring the distance and reddening to stars from their PanSTARRS1 and 2MASS photometry, based on a technique presented in Green et al. (2014, 2015) and implemented intheir 3D “Bayestar” dust map of three-quarters of the sky. We then refine the Green et al. technique by using thevelocity slices of a CO spectral cube as dust templates and modeling the cumulative distribution of dust along the lineof sight towards these stars as a linear combination of the emission in the slices. Using a nested sampling algorithm,
we fit these per-star distance-reddening measurements to find the distances to the CO velocity slices towards eachstar-forming region. This results in distance estimates explicitly tied to the velocity structure of the molecular gas. We
determine distances to the B5, IC348, B1, NGC1333, L1448, and L1451 star-forming regions and find that individualclouds are located between ≈ 275 − 300 pc, with typical combined uncertainties of ≈ 5%. We find that the velocity
gradient across Perseus corresponds to a distance gradient of about 25 pc, with the eastern portion of the cloud42

farther away than the western portion. We determine an average distance to the complex of 294 ± 17 pc, about 60
pc higher than the distance derived to the western portion of the cloud using parallax measurements of water masers
associated with young stellar objects. The method we present is not limited to the Perseus Complex, but may be
applied anywhere on the sky with adequate CO data in the pursuit of more accurate 3D maps of molecular clouds inthe solar neighborhood and beyond.
Accepted by ApJ
https://arxiv.org/pdf/1803.08931

66

RadFil: a Python Package for Building and Fitting Radial Profiles for Interstellar Filaments
Catherine Zucker1 and Hope How-Huan Chen1,2
1

Harvard-Smithsonian Center for Astrophysics, 60 Garden St. Cambridge, MA 02138, USA; 2 Department of Astronomy, The University of Texas, Austin, TX 78712, USA
E-mail contact: catherine.zucker at cfa.harvard.edu
We present RadFil, a publicly available python package that gives users full control over how to build and fit radial
density profiles for interstellar filaments. RadFil builds filament profiles by taking radial cuts across the spine of afilament, thereby preserving the radial structure of the filament across its entire length. Pre-existing spines can be
inputted directly into RadFil, or can be computed for the user as part of the RadFil workflow. We provide Gaussianand Plummer built-in fitting functions, in addition to a background subtraction estimator, which can be fit to theentire ensemble of radial cuts or an average radial profile for the filament. Users can tweak parameters like the radial
cut sampling interval, the background subtraction estimation radii, and the Gaussian/Plummer fitting radii. As aresult, RadFil can provide treatment of how the resulting filament properties rely on systematics in the building andfitting process. We walk through the typical RadFil workflow and compare our results to those from an independent
radial density profile code obtained using the same data; we find that our results are entirely consistent. RadFil canbe obtained via GitHub or installed via pip. Also on GitHub, users will find a complete working tutorial of the code
available as a jupyter notebook, which users can download and run themselves.
Accepted by ApJ
https://arxiv.org/pdf/1807.06567

Abstract submission deadline
The deadline for submitting abstracts and othersubmissions is the first day of the month. Abstracts
submitted after the deadline will appear in the following month’s issue.

43Meetings

Orion Uncovered
Leiden (The Netherlands), August 26-30, 2019
Rationale:
Since decades, Orion has been traditionally used as local benchmark for all our star-formation theories. During thelast years, a new generation of observational and theory works are revolutionizing our description of this region at
multiple scales. The whole community is invited to join this workshop to discuss the current state-of-the-art andfuture perspectives on the star-formation studies in Orion.

Concept:
The aim of this workshop is to maximize the collaboration and exchange of ideas among researchers from different
fields. With that purpose, the meeting will be divided in two parts, in a similar setup as the one we pioneered for“Orion (un)plugged” in Vienna in 2015:• Part I: online presentations (August 26-27)
To set the scene, we will review the latest results in Orion with a series of online talks. This not only includes
observational results, but also relevant theory and simulations, as well as Orion in the context of the Milky Way as awhole and nearby galaxies. With an online conferencing system, we will have participant presentations for a few hours
a day, with time slots that should be convenient for the majority of the participants. To maximize the impact andlegacy of these contributions, all talks will be broadcasted and stored as part of our YouTube channel (link) and will be
open to the entire community. Participants are invited to give their presentations either from their home institutions
or directly from Leiden.
• Part II: un-conference (August 28-30)
The second half of the workshop will be held at the Leiden Observatory. This Part II will be dynamically scheduled
following the format of an un-conference meeting. For that, participants are encouraged to propose, vote, and discuss
topics of their interests on the spot. Different rooms and screens will be available to maximize the interactions anddiscussions among participants and groups. To facilitate these interactions, this second part will be restricted to 50
participants.
• While we encourage to join both online (Part I) and un-conferenced (Part II) sessions, applicants are invited toparticipate in any of the two parts independently.
• No experience in this type of workshop is required.
• This workshop has no registration fee.
• Limited funds are available in support of young researchers.

SOC: Alvaro Hacar, Jan Forbrich, Jõao Alves, Paula Teixeira
REGISTRATION DEADLINE: June 15, 2019
Conference website: https://sites.google.com/view/OrionLeiden2019

44

The second international workshop

The UX Ori type stars and related topics
September 30 - October 4, 2019,
St. Petersburg, Russia
Organizers; Crimean Astrophysical Observatory of RAS and the Star Formation Team of the Pulkovo Observatoryof RASThe UX Ori type stars (or UXORs) are the photometrically most active young objects, predominantly Herbig Aestars. They demonstrate aperiodic algol-like minima with amplitudes up to ∆V = 2 − 3m and duration from a few
days to a few weeks. The brightness variations are accompanied by changes in color, linear polarization and spectra.
The most natural explanation of the observed phenomena is a model of variable circumstellar (CS) extinction taking
into account scattered radiation from the CS disks. The source of the variable CS extinction is the perturbations in
the innermost regions of the CS disks. Therefore the photometric behavior of UXORs is an important, and in somerespects unique source of information about the dynamical state of these regions. In recent years extinction events on
different timescales have been observed in several T Tauri stars. An important step in the study of such objects wasmade with the help of photometric observations from space: the CoRoT and Kepler missions. They have shown thatthe small-amplitude extinction events (dips) of different types (periodic or aperiodic) have been frequently observedin T Tauri stars. In this case the main source of the variable extinction are the dusty disk wind and the regionof interaction of CS disk with the stellar magnetosphere. The goal of our workshop is to discuss the observational
properties of UXORs and related objects in the light of new theoretical models.
The main topics are:
Photometry, polarimetry and spectroscopy of UXORs,Infrared activity of UXORs and related objects,
The circumstellar disks, disk winds and the nearest environment of young stars,
Shadows on the disks, the disks in polarized light,
Hydrodynamic processes in protoplanetary disks, periodic perturbations and planet formation,
The UXOR phenomena in T Tauri stars, connection with the AA Tau variables and dippers,
The evolutionary trends of the UXORs activity
SOC: Silvia Alencar, Jerome Bouvier, Konstantin Grankin, Vladimir Grinin (co-chair), Sergej Lamzin, Geoffroy
Lesur, Agnes Kospal, Antonella Natta, Rene Oudmaijer, Alla Rostopchina-Shakovskaya (co-chair)
Confirmed invited speakers:
Megan Ansdell, Center for Integrative Planetary Science, University of California at Berkeley, Berkeley,Tatjana Demidova, CrAO,
Goesta Gahm, Department of Astronomy, AlbaNova University Center, Stockholm University,
Antonio Garufi, OA Arcetri, INAF
Stefano Facchini, Max-Planck-Institut for Extraterrestrische Physik, Garching,
Catrina Hamilton-Drager, Department of Physics and Astronomy, Dickinson College,
Alexander Kreplin, University of Exeter,
Rebeca Garcia Lopez, DIAS, University of Dublin,
Ignacio Mendigutia, Centro de Astrobiologia (CSIC-INTA), Departamento de Astrofisica, ESA-ESAC,
Benjamin Montesinos, Unidad Asociada Astro UAM-CSIC, Spain,Peter Petrov, CrAO,
Ilya Potravnov, ISTP,
Timo Prusti, Directorate of Science, ESTEC-ESA,
Eduard Vorobyev, Southern Federal University,
Claudio Zanni, INAF - Osservatorio Astrofisico di Torino
E-mail: uxors-2019@crao.ru
Registration: http://uxors-2019.craocrimea.ru

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First Announcement

From Gas to Stars: The Links between Massive Star and Star Cluster
Formation
16-20 September 2019, Yorkshire Museum, York UK
We are pleased to announce a conference on the formation and early evolution of massive star clusters. The aim of
the conference is to bring together the communities who study the properties of the natal giant molecular clouds, withthose who study the stellar populations. The release of Gaia DR2 in 2018 allows the structure of young stellar cluster
and associations to be defined well for the first time. It also allows us to study more embedded structures, before
the gas is fully dispersed. By contrasting the results obtained in this way with those that study the gas and dust
component, in particular results from Herschel and ground based follow-ups with arrays such as ALMA and NOEMA,
we can hope to understand how these massive star formation regions change as they evolve. Bringing these separate
communities together in this way is especially timely. We also plan to bring together those with an overall view of thelarger scale pictures of how such structures form in the first place down to those who are more interested in how theaccretion disks from which the stars are formed feed and are disrupted in the cluster environment.
The conference will combine observational and theoretical aspects, with topics including:• The global picture of young star clusters and giant molecular clouds in the Galaxy.
• Properties of star forming clouds.
• Evolution of molecular clouds: feedback and dissipation.
• Population and structures of young clusters and OB associations.
• Dynamics of young clusters and OB associations.
• Protostars in clusters.
Confirmed Invited Speakers Tristan Cantat-Gaudin, Timea Csengeri, Adam Ginsburg, Helen Kirk, Marina
Kounkel, Michael Kuhn, Yueh-Ning Lee, Richard Parker
Scientific Organising Committee
Hervé Bouy, Ignacio de la Calle, Paul Clark, Roberto Galván-Madrid, Alvaro Hacar, Stuart Lumsden (chair), EstelleMoraux, Rene Oudmaijer, Stefanie Walch
Venue
The conference will be held at the Yorkshire Museum, in the heart of York, an ancient city in the north of England(https://www.visityork.org/) York has excellent rail connections to Leeds, London and Manchester.
Abstract submissions
Abstract submissions can be made now for both posters and talks. Our aim is to give preference where possible toearly career researchers. The deadline for submission is 30th June for both.
Registration Fee
The registration fee for the conference is £300. This will include coffee, lunches and the conference dinner. Registration
will close on 31st July. Conference details can be found on our website. If you have any questions about the conference
then please contact us by email.
Conference Website
Both abstract submissions and registration are now open at:https://starformmapper.org/final-conference/46Young European Radio Astronomers Conference 2019
26th - 29th August 2019, Dublin, Ireland
https://dias.ie/yerac2019/
Throughout its 50 year history, the Young European Radio Astronomers Conference (YERAC; http://www.yerac.org/)
has brought together postgraduate and early-career radio astronomers working at European institutions in order tofacilitate networking, raise awareness of new developments in radio astronomy and aide in professional development.
This year, the Dublin Institute for Advanced Studies has been chosen to host YERAC with financial support from RadioNet (https://www.radionet-org.eu/radionet/). All radio astronomy-related PhD students, and early career researchers, working at European institutions are encouraged to apply for a total of 30 places, for which they are expected
to give a presentation about their work within radio astronomy. Please see https://dias.ie/yerac2019/registration.html
for details on how to apply.

European Conference on Laboratory Astrophysics ECLA 2020:
Linking dust, ice and gas in space
19 - 24 April 2020, Capri, Italy
The interplay between ubiquitous dust, ice and gas in space knits an interesting tale from collapsing interstellar clouds
to the formation of new stars, planets, moons and comets. Along this path the formation of complex organic molecules
necessary to construct the building blocks of life brings us a step closer to the understanding of the evolution of life.
The advancement in the understanding of these vast intricacies of space lies in the development of varied laboratory
techniques together with astronomical observations and astrophysical modeling.
The conference allows us an opportunity to ensure collaborations between scientists active in different research fields,
which range from astronomy to geology and from chemistry to instrumentation. Further, new results will be discussed
and ideas will be exchanged from interdisciplinary perspectives to address questions that will guide observations withthe upcoming astronomical large-scale facilities, such as the James Webb Space Telescope.

Summerschool on Protoplanetary Disks and Planet Formation
We are pleased to announce the NBIA Summer School on ”Protoplanetary Disks and Planet Formation” hosted by
the Niels Bohr International Academy at the Niels Bohr Institute that will take place August 5-9 in Copenhagen.
Registration is open until May 15, 2019.
Further details about the school can be found at
http://nbia.nbi.ku.dk/nbia-school-2019
We will very much appreciate it if you could forward this email to MSc and PhD students.
Best regards,
Martin Pessahon behalf of the organizers

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Summary of Upcoming Meetings

New Horizons in Planetary Systems
13 - 17 May 2019 - Victoria, Canada
http://go.nrao.edu/NewHorizons
Exploring the Infrared Universe: The Promise of SPICA
20 - 23 May 2019, Crete, Greece
http://www.spica2019.org
Workshop on Polarization in Protoplanetary Disks and Jets
20 - 24 May 2019, Sant Cugat del Vallès, Catalonia, Spain
http://sites.google.com/view/sant-cugat-forum-astrophysics/next-session
Cloudy Workshop
20 - 24 May 2019, University of Kentucky, USA
http://cloud9.pa.uky.edu/~gary/cloudy/CloudySummerSchool/
Star Clusters: from the Milky Way to the Early Universe
27 - 31 May 2019, Bologna, Italy
http://iausymp351.oas.inaf.it/
Partially Ionised Plasmas in Astrophysics
3 - 7 June 2019, Palma de Mallorca, Spain
http://solar1.uib.es/pipa2019/
Zooming in on Star Formation - A tribute to Åke Nordlund
9 - 14 June 2019, Nafplio, Greece
http://www.nbia.dk/nbia-zoomstarform-2019
From Stars to Planets II: Connecting our Understanding of Star and Planet Formation
17 - 20 June 2019, Gothenburg, Sweden
http://cosmicorigins.space/fstpii
Gaia’s View of Pre-Main Sequence Evolution. Linking the T Tauri and Herbig Ae/Be Stars
18 - 21 June 2019, Leeds, UK
https://starry-project.eu/final-conference
Gordon Conference on Origins of Solar Systems: Meteoritical, Spacecraft and Astrophysical Perspectives on the Assembly and Composition of Planets
23 - 28 June 2019https://www.grc.org/origins-of-solar-systems-conference/2019/
Astrochemistry: From nanometers to megaparsecs - A Symposium in Honour of John H. Black24 - 28 June 2019, Gothenburg, Sweden
https://www.chalmers.se/en/conference/JHBlacksymp2019/
Smoothed Particle Hydrodynamics International Workshop
25 - 27 June 2019, Exeter, UK
http://spheric2019.co.uk/
Great Barriers in Planet Formation
21 - 26 July 2019 Palm Cove, Australia
https://dustbusters.bitbucket.io/great-barriers-2019/
Summer School Protoplanetary Disks and Planet Formation
5 - 9 August 2019 Copenhagen, Denmark
http://nbia.nbi.ku.dk/nbia-school-201948

Orion Uncovered
26 - 30 August 2019 Leiden, The Netherlands
https://sites.google.com/view/OrionLeiden2019

Understanding the Nearby Star-forming Universe with JCMT
26 - 30 Aug 2019 Courmayeur, Italy
http://www.stsci.edu/contents/events/jwst/2019/august/understanding-the-nearby-star-forming-universe-with-jw
Celebrating the first 40 Years of Alexander Tielens’ Contribution to Science: The Physics and Chemistry of the ISM
2 - 6 september 2019, Avignon, France https://tielens2019.sciencesconf.org
From Gas to Stars: The Links between Massive Star and Star Cluster Formation
16-20 September 2019 York, UK
https://starformmapper.org/final-conference/
Crete III - Through dark lanes to new stars Celebrating the career of Prof. Charles Lada
23 - 27 September 2019 Crete, Greece
http://crete3.org
The UX Ori type stars and related topics
30 September - 4 October 2019 St. Petersburg, Russia
http://uxors-2019.craocrimea.ru
Linking Dust, Ice, and Gas in Space19 - 24 April 2020, Capri, Italy
http://frcongressi.net/ecla2020.meet
COOL STARS 21: Cambridge Workshop on Cool Stars, Stellar Systems and the Sun
21 -26 June 2020, Toulouse, France
https://coolstars21.github.io/
The Physics of Star Formation: From Stellar Cores to Galactic Scales
29 June - 3 July 2020 Lyon, France https://cral.univ-lyon1.fr

49

Short Announcements

Fizeau exchange visitors program - call for applications
Electronic mail: fizeau@european-interferometry.eu

Dear colleagues!
The Fizeau exchange visitors program in optical interferometry funds (travel and accommodation) visits of researchers
to an institute of his/her choice (within the European Community) to perform collaborative work and training on one of
the active topics of the European Interferometry Initiative. The visits will typically last for one month, and strengthen
the network of astronomers engaged in technical, scientific and training work on optical/infrared interferometry. The
program is open for all levels of astronomers (Ph.D. students to tenured staff), with priority given to PhD students
and young postdocs. non-EU based missions will only be funded if considered essential by the Fizeau Committee.
Applicants are strongly encouraged to seek also partial support from their home or host institutions.
The deadline for applications is May 15 for visits to be carried out between mid July 2019 and December 2019!.
Note: the next call will be issued in November 2019!
Further informations and application forms can be found at http://www.european-interferometry.eu
The program is funded by OPTICON/H2020.
Please distribute this message also to potentially interested colleagues outside of your community!
Looking forward to your applications,Josef Hron & Péter Ábrahám(for the European Interferometry Initiative)

Moving ... ??
If you move or your e-mail address changes, please
send the editor your new address. If the Newsletterbounces back from an address for three consecutive
months, the address is deleted from the mailing list.

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