The Star Formation Newsletter#325, 25-32
島 和宏

2019/09

and a total mass of ∼ 70 M! . We confirm that R Mon drives a bipolar molecular outflow, which is blue-shifted northof R Mon. The blue-shifted outflow has excavated the molecular cloud north of R Mon, creating the reflection nebula
NGC 2261 and filling it with high-velocity gas. At “high’ velocities the orientation of the outflow is approximatelyn-s, which agrees with the optical jet, suggesting that the accretion disk is e-w. The outflow velocities are modest,± 9 km/s. The outflow is rather massive, ∼ 0.56 M! in the blue-shifted outflow lobe. The outflow is completely
optically thick in CO(3–2) towards R Mon, indicating that it’s envelope is <∼ 2,000 au. The mass of the accretion disk
and surrounding envelope determined from an isothermal graybody fit is ∼ 0.34 M! . We estimate a mass loss rateof ∼ (1 - 3) × 10−5 M! yr−1 , corresponding to an accretion rate of (1 - 9) × 10−6 M! yr−1 . We find that R Mon
has bolometric luminosity of < 1000 L! . R Mon is still in an active accretion phase, contributing to the observed
luminosity. Hence R Mon cannot be a B0 star. It must be a late B star or even an early A star.
Accepted by The Astrophysical Journal

Laboratory Experiments on the Motion of Dense Dust Clouds
Niclas Schneider1 and Gerhard Wurm1
1

Faculty of Physics University of Duisburg-Essen Lotharstr. 1, 47057 Duisburg, Germany
and a total
massniclas.schneiderof ∼ 70 M! . We
that R Mon drives a bipolar molecular outflow, which is blue-shifted northE-mailcontact:
at confirm
uni-due.deof R Mon. The blue-shifted outflow has excavated the molecular cloud north of R Mon, creating the reflection nebula
In laboratory experiments, we study the motion of levitated, sedimenting clouds of sub-mm grains at low ambient
NGC 2261 and filling it with high-velocity gas. At “high’ velocities the orientation of the outflow is approximatelypressure and at high solid-to-gas ratios !. The experiments show a collective behavior of particles, i.e. grains in clouds
n-s, which agrees with the optical jet, suggesting that the accretion disk is e-w. The outflow velocities are modest,
settle faster than an isolated grain. In collective particle clouds, the sedimentation velocity linearly depends on ! and± 9 km/s. The outflow is rather massive, ∼ 0.56 M! in the blue-shifted outflow lobe. The outflow is completely
linearly depends on the particle closeness C. However, collective behavior<only sets in at a critical value !crit which
optically thick in CO(3–2) towards R Mon, indicating that it’s envelope is 2,000 au. The mass of the accretion disk
linearly increases with the experiment Stokes number St. For St < 0.003∼particles always behave collectively. For
and surrounding envelope determined from an isothermal graybody fit is ∼ 0.34 M! . We estimate a mass loss rate
large Stokes numbers,
large solid-to-gas ratios are needed to trigger collective behavior, e.g. !
= 0.04 at St = 0.01.
of ∼ (1 - 3) × 10−5 M! yr−1 , corresponding to an accretion rate of (1 - 9) × 10−6 M! yr−1crit. We find that R Mon
Applied to protoplanetary disks, particles in dense environments will settle faster. In balance with upward gas motions
has bolometric luminosity of < 1000 L! . R Mon is still in an active accretion phase, contributing to the observed(turbulent diffusion, convection) the thickness of the midplane particle layer will be smaller than calculated based on
luminosity. Hence R Mon cannot be a B0 star. It must be a late B star or even an early A star.
individual grains, especially for dust. For pebbles, large solid-to-gas ratios are needed to trigger instabilities based on
Accepted by The Astrophysical Journal
back-reaction.
Accepted by ApJL

Laboratory Experiments on the Motion of Dense Dust Clouds
http://arxiv.org/pdf/1912.01714
Niclas Schneider1 and Gerhard Wurm1
1
Facultyof Physicsof
University
Duisburg-Essen
Lotharstr.
1, 47057 Duisburg,
GermanyTheevolution
dust inofdiscs
influenced
by external
photoevaporation
1
E-mail contact:
niclas.schneider
Andrew
D. Sellek, Richard at
A.uni-due.de
Booth1 and Cathie J. Clarke1
1
InInstitutelaboratory
experiments,
we studyofthemotion ofMadingleylevitated, Road,
sedimenting
cloudsof sub-mm
of Astronomy,
University
Cambridge,
Cambridge
CB30HA, UKgrains at low ambientpressure and at high solid-to-gas ratios !. The experiments show a collective behavior of particles, i.e. grains in clouds
E-mail contact: ads79 at cam.ac.uk

as binary candidates by the Gaia survey.
Accepted by MNRAS
http://arxiv.org/pdf/1912.02806

Long-term multi-frequency maser observations of the intermediate-mass young stellar
object G107.298+5.639
Mateusz Olech1 , Marian Szymczak1 , Pawel Wolak1 , Eric Gérard2 and Anna Bartkiewicz1
1

Institute of Astronomy, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, Grudziadzka
5, 87-100 Torun, Poland; 2 GEPI, UMR 8111, CNRS and Observatoire de Paris, 5 Place J.Janssen, 92195 Meudon
Cedex, France
21
E-mail contact: olech at astro.umk.pl

Periodic flares of maser emission are thought to be induced either by variations of the seed photon flux in young
binary systems or the pump rate regulated by stellar and accretion luminosities. We seek to study the variability offour maser transitions of three different species in G107.298+5.639 to constrain the dominant mechanism of periodic
flares. Light curves of the 6.7 GHz methanol and 22.2 GHz water vapour maser were obtained with the Torun 32m
radio telescope over 39 and 34 cycles, respectively. The target was also monitored at the 1.6 GHz hydroxyl transitions
with the NanŊay radio telescope over 13 cycles. All these maser lines were imaged using VLBI arrays. The study
confirms alternating flares of the methanol and water masers with a period of 34.4d and reveals the synchronised
behaviour of the methanol and hydroxyl masers in this source. The observed spatial distribution of the methanol
maser cloudlets and the measured time delays of the flares of individual features imply a ring-like structure of radius
240au and thickness 30au. Internal proper motions indicate that the velocity of methanol cloudlets is dominated by adisc-wind component of about 5km/s. The methanol emission detected during only one VLBI observation is locatedin a region about 550au from a central star, which also exhibits OH maser flares. The erratic appearance of methanolfeatures can be related to a powering object of relatively low luminosity which, during some variability cycles, canexcite molecules only in the nearest part of the disc. A careful analysis of the maser and infrared light curves reveala strong correlation between the 6.7 GHz line and the infrared flux densities supporting a radiative pumping of themaser. The synchronised behaviour of the hydroxyl and methanol lti-266()-1(i)-196n-256(sr)388(n278(findi-347(c-2429(d)6()-5(e-25

EVN(Jb,Ef,Mc,O8,Tr,Nt,Wb,Ys,Sr)
EVN(Jb,Ef,Mc,O8,Tr,Nt,Wb,Ys,Sr,T6,Ir)
EVN(Jb,Ef,Mc,O8,Tr,Nt,Wb,Ys,T6)
VLBA(BR,FD,HN,KP,LA,MK,NL,OV,PT,SC)

57444
57544
57681
57906

6668.519
6668.519
6668.519
22235.080

0.09
0.09
0.09
0.11

57600

57800

5.2⇥3.2; 61.38
4.2⇥2.8; 76.25
4.2⇥3.1; 79.75
0.6⇥0.5; -1.10

3.0
2.5
5.0
5.0

189
172
171
104

Notes. No data were used from italicised stations

2000

0
100

0
2

0
2

0
57000

57200

57400

58000

58200

58400

OH 1.667 GHz

10.03
0.44
> 5.9410.83 (1.06) 0.54 (0.15)
2.91 (0.44)
14.00
0.65
> 1.41
9.87 (1.94) 0.77 (0.38)
2.63 (0.53)
9.62
0.32
> 1.2511.10 (3.83) 1.10 (0.50)
1.02 (0.90)
18.83
42.00
22.49 (18.01) 15.61 (2.32) 1.29 (0.48)
0.19 (0.41)
16.40
218.60 146.51 (64.10) 17.62 (1.49) 1.19 (0.44)
07.85 M.36.59
15.79 (1.86)in G107.298+5.639
1.15 (0.49)
0.50 (0.64)
Olech et18.70
al.: (26.68)
Maser observations−1

Hydroxyl integrated flux density (Jy km s )約34日周期
H2 O 22 GHz
OHメーザーはちょっと遅れてる

3.0
2.5
2.0

1665MHz
1667MHzr = 0.677 (p<0.0001)
r = 0.405 (p<0.0004)

1.5
1.0
0.5
0.0
0.1

1

10

−1

Methanol integrated flux density (Jy km s )100

Fig. 3. Lomb-Scarglelines) calculated
the inFig. 6. periodograms
Correlation(black
betweenthe OHfor1.665/1.667
GHz and CH3 OH
tegrated flux time series in each of the observed transitions. The red
6.7 GHz maser integrated flux densities. The open symbols denote thedashed line represents a 0.01% false alarm probability level.

Fig. 2. Phased and normalised light curves of the integrated flux in each
upper limits for at least one transition. The solid lines show the best fitsobserved transition (grey points). Red points show binned light curves,
Fig. 5.
Propermotionsofthemethanolmaser
cloudlets
in
G107
as
meato the data.
with 0.05P and 0.1P bins for the 6.7, 22 GHz and both OH lines, respecsuredtively.
relativetotheircentreofmotiondenoted
by
small
black
cross.
The red line represents the best fit of asymmetric periodic powerfunction.
All thecurvesmotions
are foldedin
modulod, thelisted
variability
Cones represent
thelight
propereach 34.43
cloudletin Table A.2
The water maser emission was detected in two clusters
periodofthemethanolemission,andthedashedvertical
lines
show
the
and their colours and apertures correspond to the radial velocity (colour
placed within ⇠200 mas of each other just between the two
main
peaks of the 6.7 GHz flare.
OH cloudlets at about 12.2 km s 1 located ⇠250 mas north of

メタノールメーザーとOHメーザーの強度に相関bar) and uncertainty, respectively. The velocity scale is showngroups
at theof methanol masers (Fig. 4). These water maser clusters
the velocity
region of(Fig. 4) coincide withindi↵er in radial
in apersistentsimilar waymethanol
to those ofmasers
methanol
top right corner. The dashed ellipse displays the model of ring derived->
同じ励起機構によるもの？
masers.
interesting
theau)
relative
andat
radialve- the methanol maser
mas that(100
withpositions
an area
whichfrom the 3D structure analysis shown in Fig. 7, where the yellow
star It is<120
locities of thesewater maser
clusters between
are similar -15.6
to thoseand
seen-13.7 km s 1 appearedof velocity
shows the positionof fitted centre of the ring.
The grey star denotes
the emission
1
1
15.0 km s ) and SE ( 9.3 to 7.1 km s ) groups of methanol ten years ago (Hirota et al. 2008). However, the morphology ofpositionof themm well
continuum(Palauofetblueal. 2011).
the notsecondepoch(MJD 57444)
masersthat1.3
agreeswith thepeak
velocities
and red- the westernduring
cluster does
resemblethat observedby Hirotaof VLBI observations
shifted lobes of outflows observed in the CO lines (Palau et al.
2011).

A.4). Since
flux densities
of both masers are strongly
et al. (2008),(Fig.
who interpreted
it as thean expanding
shell. Moreover,at the epocha↵ectedof our observation(MJDfiltering
57901) no bywaterthemaser
was as Fig. A.4 depictsby spatial
VLBI,

M. Olech et al.: Maser observations in G107.298+5.639−1

Hydroxyl integrated flux density (Jy km s )A&A proofs: manuscript no. pap_g107_corr3 face-on 想像図
3.0

masers (Cragg et al. 2002) and the coincidence of these transi-2.5
disk common
wind?
tions in G107 supports
excitation processes which produce the population inversions simultaneously in both molecules2.0
and result in synchronised variability of maser flux densities.
4.2. Anti-correlated variability of CH3 OH and H2 O masers

1665MHz
1667MHzr = 0.677 (p<0.0001)
r = 0.405 (p<0.0004)

1.5
1.0

The present study reinforces our previous finding of alternating
variations of the methanol and water masers in the source (Szym-0.5
czak et al. 2016). The methanol maser flare exactly coincides
with the water maser minimum for all 33 cycles monitored over0.0
ring-like⇠3.5 yr (Figs. 1, 2). Furthermore, the water maser emission that
0.1
1
10
100
appeared outside the methanol velocity range, i.e. from 23 to−1
Methanol integrated flux density (Jy km s )17 km s 1 and greater than 5 km s 1 , also shows periodic variability. All the water maser cloudlets lie well within the methanolFig. 6. Correlation between the OH 1.665/1.667 GHz and CH3 OH
bounded region of projected size less than 200 au (Fig. 4). Thus,
6.7 GHz maser integrated flux densities. The open symbols denote theit is likely that the methanol and water masers operate in regions
upper limits for at least one transition. The solid lines show the best fits
Fig.of
5. similar
Proper motionsofthemethanolmaser
cloudlets
in
G107
as
meaphysical parameters, where a factor causing periodic
to the data.
sured
relativetotheircentreofmotiondenoted
by
small
black
cross.
changes is efficient.
Cones represent the proper motions in each cloudlet listed in Table A.2
excitation
mechanisms
6.7velocity
GHz (colourand 22 GHz
and theirThecolours
and apertures
correspond toofthetheradialOHiscloudlets at about 12.2 km s 1 located ⇠250 mas north ofbar)masers
and uncertainty,
respectively.
velocity
scale theis shown
at the line
are understoodin Thegeneralterms;
methanol
ディスクモデルが一番良さそう
the region of
persistent methanol masers (Fig. 4) coincide within
top likely
right corner.
The dashedellipse displays
modelSobolevof ring derived
invertedby infrared
photonsthe(e.g.
et al. 1997;<120 mas (100 au) with an area at which the methanol maser
fromthe 3Detstructure
analysisin Fig. line
7, where
the yellow star colliCragg
al. 2002)
whileshown
the water
is predominantly
between-15.6 and -13.7 km s 1 appearedshows the position of fitted centre of the ring. The grey star denotes the emission ofrvelocity=
240
AU
sionally(e.g. Elitzural. 1989;
Gray et al. 2016). Thepositionof thepumped
1.3 mm continuum
peaket(Palauet al. 2011).
during the second epoch (MJD 57444) of VLBI observations
oretical models generally indicate that the gas density and(Fig.
ki- A.4). Since the flux densities of both masers are strongly
h = 30 AU
netic temperature favouring both maser transitions do not overa↵ected by spatial filtering by the VLBI, as Fig. A.4 depictslap (Cragg
et al. 2002;
Grayproper
et al.motions
2016). in
However,modelling
powering
star. Somewhat
randomthis site may
the above discussed spatial di↵erences could be much smaller
resultfrom22
theGHzmethodof proper
motionstudies
we applied.
We forof themaser
excitation
withup-to-datemolecular
datalow brightness extended emission. Thus, the hydroxyl andcalculated
the properwithbarycentre(Nesterenok2013)motions
supports
therespect
view tothatthethe
inversionofis mostmethanol masers originate in basically the same gas volume at amethanol
distribution
the exciting
star. We
postponeof 200 420 au from the central protostar. We note that
efficientwhen therather
dust thantemperature
is muchlower
thanathedistancegas
detailed
analysisandof plausible
causesof theobserved
properreduces
mo- thetemperature
an increaseof theinfraredemission
theprojected size of ⇠450 au of the methanol maser region durtions
becausethemaser
exhibits
notonly
significant
variations
ining the three epochs is close to the lower limit of the disc sizes
maser gain (Yates et al. 1997).
the amplitude of flare and its profile, as the single dish monitor-

observed in intermediate-mass embedded protostars (Beltrán &distributed. Using the minimum spanning tree analysis, we found 26 probable sub-clusters having 5 or more members.
The sub-clusters are between ∼0.5 pc – ∼3 pc in size and are somewhat elongated. The star formation efficiency inmost of the sub-cluster region varies between 5% – 20% indicating that the sub-clusters could be bound regions. The
radii of these sub-clusters also support it.
Accepted by MNRAS
http://arxiv.org/pdf/1912.11789

Probing the early phases of high mass star formation with 6.7 GHz methanol masers
Sonu Tabitha Paulson1

6.7GHz メタノールメーザー-> 本当に大質量星形成領域に付随しているのか？
Methanol Multibeam survey: 972 sources のうち・Infraredの観測データがある
・距離が分かっている
320天体を調査

Paulson & PandianApplied to protoplanetary disks, particles in dense environments will settle faster. In balance with upward gas motions(turbulent diffusion, convection) the thickness of the midplane particle layer will be smaller than calculated based on
individual grains, especially for dust. For pebbles, large solid-to-gas ratios are needed to trigger instabilities based on
back-reaction.

32

Accepted by ApJL
http://arxiv.org/pdf/1912.01714

The evolution of dust in discs influenced by external photoevaporation
Andrew D. Sellek1 , Richard A. Booth1 and Cathie J. Clarke1
1

Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK

E-mail contact: ads79 at cam.ac.uk
Protoplanetary discs form and evolve in a wide variety of stellar environments and are accordingly exposed to a wide
range of ambient far ultraviolet (FUV) field strengths. Strong FUV fields are known to drive vigorous gaseous flows
from the outer disc. In this paper we conduct the first systematic exploration of the evolution of the solid componentof discs subject to external photoevaporation. We find that the main effect of photoevaporation is to reduce thereservoir of dust at large radii and this leads to more efficient subsequent depletion of the disc dust due to radial drift.
Efficient radial drift means that photoevaporation causes no significant increase of the dust to gas ratio in the disc.
We show that the disc lifetime in both dust and gas is strongly dependent on the level of the FUV background andthat the relationship between these two lifetimes just depends on the Shakura-Sunyaev α parameter, with the similar
lifetimes observed for gas and dust in discs pointing to higher α values (∼ 10−2 ). On the other hand the distributionof observed discs in the plane of disc size versus flux at 850 µm is better reproduced by lower α (∼ 10−3 ). We find thatphotoevaporation does not assist rocky planet formation but need not inhibit mechanisms (such as pebble accretionat the water snow line) which can be effective sufficiently early in the disc’s lifetime (i.e. well within a Myr).
Accepted by MNRAS
https://arxiv.org/pdf/1912.06154

24

sibleh andthe heating (Kenyon & Hartmann 1987; Chiang & Goldreich 1997)
g inevoluWe model the viscous evolution of the gas and growth and radial- is supported by mean fits of the SED shape for q (Andrews &partialr, the Modelmigration of the dust as in Booth et al. (2017) for which the treatment
Williams
2005; Kenyon & Hartmann 1995) and the corresponding
ations) unof thedependence
dust followsofthatof Birnstieletal. (2012).
We employa midlinear
viscosityondiscradiusisalsoconsistent
withradial temperature proﬁle modeldnets;
dust mid-plane
planeradial temperature
profile T(R)modeledaccordingto:theobservedvariationofaccretion
rates
onto
T
Tauri
stars
as a
tetainii) to✓of age◆ q(Hartmann et al. 1998).
functionR
scsin(q=0.5) scale, we set the aspect ratio (the (1)2). ToT =T. a temperature
In
order
to
set
0
arietyR0
1/4starthese
R=1
au でT~279
K as
for
1M
ratio
of
scale
heightHoverradius,whichscales
H/R
/
R
) to
sun
7; Trion is
H/R⇠ 0.033
at R0 = 1 ↵auviscosity
such that Tprescription
a 1 M star.
As
Assuming
a constant& Sunyaev
0 ⇡ 279 K for(Shakura
affects
ourinitialwe viscosity
adopt the similarity
solution
Lynden-Bellonof1973),
thecondition
kinematic⌫ then scales
withofradiusaslatter& Pringle(1974)
forthesurfacedensity,⌃:ofthe surface
essingvisc / R3/2 q .
⌫ / R density
(2)

ement
2005)
ust inducttion.

at areon oflished012)
h018b)
andouter
volubackartialns (intions
been6)dustandii) to
simu-

✓

◆

✓

◆2

R spatially uniformR
We explore↵ values motivated by the range of
total disk
mass = 100⌃ = ⌃0
exp
,
(3)MJ
3
viscosities(Rafikov 2017) and
RC inferred from
RC observations: 10
2 (Hartmann et al. 1998). Following Clarke (2007) and Facchini
10
where = visc (Equation 2) and RC is the scale radius of the exet al. (2016)
we(i.e.
thenq = 0.5
suchthat⌫radiusisRlinearwithponential
cut off
RC choosesets theinitialextentof thedisc).
C was
exponential
cutoﬀ
radius.between
This dependence- whichresults
if stellarof dustvaried10 and 300 au.
The values
adoptedare irradiation
roughly in thein thederived
form ofthesubmm
blackbodyequilibrium
temperature
dominates
range
from
continuum
observationsof protoplanethe heating(Kenyon1987; Chiang& Goldreich
tary
discs (e.g.
Ansdell&etHartmannal. 2018; Tripathi
et al. 2017),
although1997)
accretion
following
the should
viscousmotionofthethiscoincidewith
the &- is observational
supportedbymeasuremean
fitsof notthenecessarily
SED shapefor qgas(Andrews
initial,mass-based
measureradiustherepresented
by theRC .corresponding
The denWilliams
2005;&ofHartmann
1995)+ radial
drift
dueKenyon
to dragfromgas andsity
normalisation,⌃ofis set by the
total
disc
mass.
Observational
0 , viscosity
lineardependenceon
discradiusisalsoconsistent with+ photoevaporation due to FUV irradiation
studiesmeasurevariation
dust massesof up to ⇠100ontoM T(e.g.
141stars
M as athe observedof accretion
rates
Tauri
in
Lupus, ofAnsdell
et al. 2016),
corresponding
to discs with & 30
functionage (Hartmann
et al.
1998).

Dust evolution in photoevaporating discs

0.2

10 8
400

80.0%
Ṁ
acc
90.0%
Ṁ
evap
RD

10 6
150

0.0

No Photoevaporation

67
10 125

100

10 8
75
50
10 9

180

350
10 9

300

4

10 9

3

9

250

10

200

25
2

0

101.02Mass left in Disc
Mass lost to Wind
Mass lost to Star3
10 0.6

10

0.8

0.6
10 3

0.4
10 4
0.2

0.0
103

0.4

0.2
10 4

5

104

105

106

107

Time / years

0.0
103

100
10 8
80

10609

10 10

Dust Mass Fraction Md/MD

Dust Mass Fraction Md/MD
Dust Mass Md / MJ

10 2
0.8

140
10 7
120

40

10
1509

Dust Mass Fraction Md/MD
Dust Mass Md / MJ

1010

No Drift

101606

Ṁ / M yr 1
Dust Radius / AU

175

Ṁ / M yr 1
Dust Radius / AU

0.0

Full Model

1
Ṁ
/
M
yr
Dust Radius / AU

0.0

7

104

105

Time / years

106

107

0.01100.01080.01060.01040.01020.0100
103

104

105

106

107

Time / years

Figure 5. From left to right: Model RDPE including radial drift and photoevaporation, Model RD including radial drift but no photoevaporation and Model
Figure 5. PE
Fromleft to photoevaporationright: Model RDPE
includingradialandphotoevaporation,
Model
RD90including
radial drift
no cent
photoevaporation
andincludingbut noradial drift.
Thedriftpanelsshow,from top: the radiusof theper cent (orange)
and but
80 per(red) percentilesof Modelthe
PE including
but theno radius
radial ofdrift.
Thediscpanelsshow,
fromfortop:
the radiusof the90 perandlost80 to
perof thedustphotoevaporation
mass distribution withthe gas(black,dashed)reference;
the massin dustleftcent
in the(orange)
disc (blue),thecent
wind(red)(red)percentiles
and lost to the(green); theglobaldust massfraction;
the gasmassdashed)loss ratefor
throughaccretion(solid)inandphotoevaporation
In addition,
the time
the lost
dust toat thedust mass star
distribution
withthe radiusof thegas disc(black,reference;
the mass
dust
left in the disc(dashed).
(blue), lostto the wind(red)ofand
thethewindbase beginningradially drift
in andhavingthe discaccretionare shown(solid)
as the andtwo photoevaporation
black dotted lines. Notethe linear
scale on thestar (green);
globaldust masstofraction;
the gasmass
loss cleared
rate through(dashed).
In addition,
thebottom
time ofrightthe plot
dust atdue tothe small tovariationin driftthe dust
masshaving
fraction.
the wind basebeginningradially
in andcleared the disc are shown as the two black dotted lines. Note the linear scale on the bottom right plot

due to the small variation in the dust mass fraction.

Accepted by Research in Astronomy and Astrophysics
http://arxiv.org/pdf/1912.06984

Spectral library of age-benchmark low-mass stars and brown dwarfs
E. Manjavacas1,2 , N. Lodieu3,4 , V.J.S. Béjar3,4 , M.R. Zapatero-Osorio5 , S. Boudreault6 , M. Bonnefoy7
1

W.M. Keck Observatory, 65-1120 Mamalahoa Highway, Kamuela, HI 96743, USA; 2 Department of Astronomy/Steward
Observatory, The University of Arizona, 933 N. Cherry Avenue, Tucson, AZ, 85721, USA; 3 Instituto de Astrofísica

a strong correlation between the 6.7 GHz line and the infrared flux densities supporting a radiative pumping of themaser. The synchronised behaviour of the hydroxyl and methanol transitions indicates a common pumping mechanism
for the periodic flares of G107.298+5.639.

27

Accepted by Astronomy and Astrophysics
https://arxiv.org/pdf/2001.01625

Large scale star formation in Auriga region
A.K. Pandey1 , Saurabh Sharma1 , N. Kobayashi2,3 , Y. Sarugaku3 and K. Ogura4
1

Aryabhatta Research Institute of Observational Sciences (ARIES), Manora Peak, Nainital, 263 002, India; 2 Instituteof Astronomy, University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015, Japan; 3 Kiso Observatory, School of
Science, University of Tokyo, Mitake-mura, Kiso-gun, Nagano 397-0101, Japan; 4 Kokugakuin University, Higashi,
Shibuya-ku, Tokyo 150-8440, Japan
E-mail contact: pandey at aries.res.in

New observations in the VI bands along with archival data from the 2MASS and WISE surveys have been used togenerate a catalog of young stellar objects (YSOs) covering an area of about 6◦ × 6◦ in the Auriga region centered
at l ∼ 173◦ and b ∼ 1.◦ 5. The nature of the identified YSOs and their spatial distribution are used to study thestar formation in the region. The distribution of YSOs along with that of the ionized and molecular gas reveals tworing-like structures stretching over an area of a few degrees each in extent. We name these structures as Auriga
Bubbles 1 and 2. The center of the Bubbles appears to be above the Galactic mid-plane. The majority of Class i YSOs
are associated with the Bubbles, whereas the relatively older population, i.e., Class ii objects are rather randomly
distributed. Using the minimum spanning tree analysis, we found 26 probable sub-clusters having 5 or more members.
The sub-clusters are between ∼0.5 pc – ∼3 pc in size and are somewhat elongated. The star formation efficiency inmost of the sub-cluster region varies between 5% – 20% indicating that the sub-clusters could be bound regions. The
radii of these sub-clusters also support it.
Accepted by MNRAS
http://arxiv.org/pdf/1912.11789

Probing the early phases of high mass star formation with 6.7 GHz methanol masers
Sonu Tabitha Paulson1 , Jagadheep D. Pandian1
1

Department of Earth and Space Sciences, Indian Institute of Space Science & Technology, Thiruvananthapuram
695547, Kerala, India

with the majority being in the accretion phase. However, we observe a small number of sources that could possibly
be related to intermediate or low-mass stars.

Accepted by MNRAS
29

http://arxiv.org/pdf/1912.06973

Formation of moon systems around giant planets: Capture and ablation of planetesimals
as foundation for a pebble accretion scenario
T. Ronnet1 and A. Johansen1
1

Department of Astronomy and Theoretical Physics, Lund Observatory, Lund University, Box 43, 22100 Lund, Sweden

E-mail contact: thomas.ronnet at astro.lu.se
The four major satellites of Jupiter, known as the Galilean moons, and Saturn’s most massive satellite, Titan, arebelieved to have formed in a predominantly gaseous circum-planetary disk, during the last stages of formation of theirparent planet. Pebbles from the protoplanetary disk are blocked from flowing into the circumplanetary disk by the
positive pressure gradient at the outer edge of the planetary gap, so the gas drag assisted capture of planetesimals
should be the main contributor to the delivery of solids onto circum-planetary disks. However, a consistent framework
for the subsequent accretion of the moons remains to be built. Here we use numerical integrations to show that mostplanetesimals being captured within a circum-planetary disk are strongly ablated due to the frictional heating theyexperience, thus supplying the disk with small dust grains, whereas only a small fraction ‘survives’ their capture. We
then construct a simple model of a circum-planetary disk supplied by ablation, where the flux of solids through the disk
is at equilibrium with the ablation supply rate, and investigate the formation of moons in such disks. We show that thegrowth of satellites is driven mainly by accretion of the pebbles that coagulate from the ablated material. The pebbleaccreting protosatellites rapidly migrate inward and pile up in resonant chains at the inner edge of the circum-planetary
disk. We propose that dynamical instabilities in these resonant chains are at the origin of the different architectures ofJupiter’s and Saturn’s moon systems. The assembly of moon systems through pebble accretion can therefore be seen
as a down-scaled manifestation of the same process that forms systems of super-Earths and terrestrial-mass planets
around solar-type stars and M-dwarfs.
Accepted by A&A
http://arxiv.org/pdf/1912.04765

The molecular outflow from R Mon
Goran Sandell1 , W. Vacca2 , L. Bouscasse3 and R. Güsten3
1

University of Hawaii, Institute for Astronomy - Hilo, 640 N. Aohoku Place, Hilo, HI 96720, USA; 2 SOFIA Sciencen-s, which agrees with the optical jet, suggesting that the accretion disk is e-w. The outflow velocities are modest,± 9 km/s. The outflow is rather massive, ∼ 0.56 M! in the blue-shifted outflow lobe. The outflow is completely
optically thick in CO(3–2) towards R Mon, indicating that it’s envelope is <∼ 2,000 au. The mass of the accretion disk
and surrounding envelope determined from an isothermal graybody fit is ∼ 0.34 M! . We estimate a mass loss rateof ∼ (1 - 3) × 10−5 M! yr−1 , corresponding to an accretion rate of (1 - 9) × 10−6 M! yr−1 . We find that R Mon
has bolometric luminosity of < 1000 L! . R Mon is still in an active accretion phase, contributing to the observed
luminosity. Hence R Mon cannot be a B0 star. It must be a late B star or even an early A star.

31

Accepted by The Astrophysical Journal

Laboratory Experiments on the Motion of Dense Dust Clouds
Niclas Schneider1 and Gerhard Wurm1
1

Faculty of Physics University of Duisburg-Essen Lotharstr. 1, 47057 Duisburg, Germany

E-mail contact: niclas.schneider at uni-due.de
In laboratory experiments, we study the motion of levitated, sedimenting clouds of sub-mm grains at low ambientpressure and at high solid-to-gas ratios !. The experiments show a collective behavior of particles, i.e. grains in clouds
settle faster than an isolated grain. In collective particle clouds, the sedimentation velocity linearly depends on ! andlinearly depends on the particle closeness C. However, collective behavior only sets in at a critical value !crit which
linearly increases with the experiment Stokes number St. For St < 0.003 particles always behave collectively. For
large Stokes numbers, large solid-to-gas ratios are needed to trigger collective behavior, e.g. !crit = 0.04 at St = 0.01.
Applied to protoplanetary disks, particles in dense environments will settle faster. In balance with upward gas motions(turbulent diffusion, convection) the thickness of the midplane particle layer will be smaller than calculated based on
individual grains, especially for dust. For pebbles, large solid-to-gas ratios are needed to trigger instabilities based on
back-reaction.
Accepted by ApJL
http://arxiv.org/pdf/1912.01714

The evolution of dust in discs influenced by external photoevaporation
Andrew D. Sellek1 , Richard A. Booth1 and Cathie J. Clarke1
1

Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK

E-mail contact: ads79 at cam.ac.uk
Protoplanetary discs form and evolve in a wide variety of stellar environments and are accordingly exposed to a wide
range of ambient far ultraviolet (FUV) field strengths. Strong FUV fields are known to drive vigorous gaseous flows