ﬀ
+)*1

-

u

*,

&

The JCMT Transient Survey: Stochastic and Secular Variability of Protostars and Disks
15
In the Sub-Millimeter Observed Over Eighteen Months
3
1,2,4
Doug Johnstone1,25.
, GregoryJ. Herczeg, Steve, Jennifer Hatchell5 , Geoﬀrey C. Bower6 ,INDIVIDUAL
SOURCESOFMairs
INTEREST

Helen Kirk1 , James Lane2 , Graham S. Bell4 , Sarah Graves4 , Yuri Aikawa7 , Huei-Ru Vivien Chen8 ,above investigation,
we searchedstochastic
andKangsecularSurvey.
91010 variables within11the entire JCMT
13
Wen-Ping Chen
, Miju for
Kang, Sung-Ju, Jeung-Eun Lee , Oscar Morata12Transient, Andy Pon, Peter
15 candidate variable
19 variables
ction weScicluna
discuss 14individuallyeach
identified
this11,18
survey,along
with Teamseveral, Aleks Scholz, Satoko Takahashi16,17, HyunjuinYoo
and TheJCMT

in Mairs1 etal. Herzberg(2017b) andthe sub-mm
variable HOPS
383,Saanich
identified
SafronBC,et V9E
al. (2015).
Where2 possible
NRC
Astronomy
and Astrophysics,
5071 WestRd, byVictoria,
2E7, Canada;
Department
are thoseofsources
robust secularfits ofwiththe brightnesschangemeasurements
obtained
et al.andPhysics withand Astronomy,
University
Victoria,
Victoria, BC,
V8P 5C2,
Canada; 3 Kavli
Instituteby
forMairs
AstronomynL Y C<FL LeUbf]Ybg
KheiYkBeijing,
j K<M;:+Republic
Ug 1.)ofa]
ecb4 East Asian Observatory, 660 North A‘ohoku
Pekingsource
University,
China;
Mairs et Astrophysics,
al. collated mean
brightnessesPeople’s
from the Transient
Surveyagainst archival JCMT Gould Belt
5
Place,kUniversity
Park,
Hilo, Hawaii
96720,fhV
USA;
Physics
and1longer,
Astronomy,
University,
Road, five
Exeterata (Ward-Thompson
et
al.
2007)
to
investigate
variability
2-4 Exeter
year ]btimescales,
uncovering
Fcbgacb]gce]b[
gcjUeXf*/-,ndYU
f over]b
K? eY[]cbfhX]b[ Stocker**.
decgcfgUef%
6
EX4 4QL, UK; Academia Sinica Institute of Astronomy and Astrophysics, 645 N. A’ohoku Place, Hilo, HI 96720,
ndidates.
Asin Section 6 and shown inTable
7, YegU]bgk
there is significant
7 f Xcjb
8 overlap between the Mairs et al.
***USA;X]fdiscussedj]gcZ .&*)
Departmentgcofm*)aCk(VYUa
Astronomy, University
of hbTokyo,
Tokyo, Japan;
Department of Physics and Institute ofample andthe resultsfrom Tsing
this paper.
Mairs etTaiwan;al. (2017b)
did not
specificallyconsiderNational
stochastic
variability
9
Astronomy,
National
Hua University,
Graduate
Instituteof Astronomy,Central
University,
nKgUbXUeXXYi]Ug]cb
UbU
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nalysis techniqueuseddown-weighted
sourceswith large
variations
withineitherScienceor bothInstitute,data Surveys.
Thus
300 Jhongda
Road,Zhongli, Taoyuan,
Taiwan;Korea
Astronomy
and Space
776 Daedeokdae11
12
ro,compare
Yuseong-gu,
Daejeon34055,
Republicof Korea;
Schoolof Space
Research,
Kyung
Hee
University,
Korea;
ot abletodirectlythepossiblestochastic
variables
found
here
with
that
paper.
At
the
end
of
this
BXYbg]oYX Ub Ydc fhVaa pUeY gcjUeXf U decgcfgUe ><.,]b KYed FU]b ?][ + UbX
13Academia
SinicaInstituteofAstronomy
andAstrophysics,
Taiwan;Departmentof analysis
Physics andAstronomy,The
8 found to vary in the present
e present light curves for three sources that are notthebrightest
14
UniversityiUe]UVof Western
Ontario,
London,ON, N6A FU]b%
3K7, Canada;
Academia
SinicaInstituteof Astronomy
ndcgYbg]U
Y
fche
Yf
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]b
KYedYbf,]b
HF<
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]b Hd
<ceY4
LUV
Y , andbserved in the OMC 2/3 and Ophiuchus Core regions and15the second brightest
in Serpens
Main.
Astrophysics, P. O. Box 23-141, Taipei 10617, Taiwan;
SUPA, School of Physics and Astronomy, North Haugh, St
16
Andrews, KY16 9SS, United Kingdom;
Joint ALMA Observatory, Alonso de Cordova 3107, Vitacura, Santiago,
Chile; 17 National Astronomical Observatory of Japa, 2-21-1
Osawa, Mitaka, Tokyo 181-8588, Japan; 18 Department
IRAS 18270-0153
of Astronomy and Space Science, Chungnam National University, Republic of Korea; 19 All Over

1.4
E-mail contact: doug.johnstone at nrc-cnrc.gc.ca
EC 53

1.2

1 50

1.2

1

1

Jy beam

We analyze results from the first eighteen months of monthly sub-mm monitoring of eight star-forming regions in the
1.0
1.0
JCMT Transient Survey. In our search forstochastic variability in 1643 bright peaks, only thepreviously identified
0.8
0.8
source, ECSMM-10
53, shows behavior well above theexpected measurement uncertainty. Another four
sources, two disks and
16
51
0.6
two protostars, show moderately-enhanced0.6standard deviations in brightness, as expected for stochastic
variables. For
0.4 is the result of single epochs that are much brighter
0.4
the two protostars, this apparent variability
than the mean. In
SMM-1
0.2 that are linear in time, we measure the fractional
0.2brightness change per
our search for secular brightness variations
15
52
year for 150 bright peaks, fifty of which are
0.0 protostellar. The ensemble distribution of slopes0.0is well fit by a normal
distribution with σ ∼ 0.023. Most sources-0.2
are not rapidly brightening or fading in the sub-mm.
-0.2 Comparison against
time-randomized realizations shows that the width of the distribution is dominated by the uncertainty in the individual+1 14brightness measurements of the sources. A toy model53
for secularvariability
revealsthat an underlying Gaussian
s
s
s
s
h
m
s
57
54
51
48
18 29 45
45s
42s
39s
36s
33s 18h 29m 30s
distribution of linear
fractional brightness change σ = 0.005 wouldRAbe
unobservable in the present sample, whereas
RA (J2000)(J2000)Jy beam

Dec (J2000)

17

1.4

&

The evolution of young HII regions

A&A proofs: manuscript no. EYH_Internal

P.D Klaassen1 , K.G Johnston2 , J.S. Urquhart3 , J.C Mottram4 , T. Peters5 , R. Kuiper6,4 , H. Beuther4 ,F.F.S van der Tak7,8 and C. Goddi9P.D. Klaassen et al: The evolution of young Hii regions

1

ATC, UK; 2 U. of Leeds, UK; 3 U. of Kent, UK; 4 MPIA, Germany; 5 MPA, Germany; 6 U of Tubingen, Germany; 7JYXTheFKO
KheiYk 9JFK
SRON, The Netherlands; 8 Kapteyn,
Netherlands;
Radboud U. & Allegro/Leiden Observatory, The Netherlands

m/))
ABB
E-mail contact: pamela.klaassen at
stfc.ac.uk

EVc 7*)T-Efhb

6 ,&. . dthan those associated with isolated low-mass stars, and once they
High-mass stars form in much richer Xenvironments
reach a certain mass, produce ionised(Hii) regions.
:EF:+)*, The formation*aa of% these pockets of ionised gas are unique to theformation of high-mass stars (M > 8 M⊙ ), and present an excellent opportunity to study the final stages of accretion,m) .Ue fY u
<K .&-%
which could include accretion through the Hii region itself. This study of the dynamics of the gas on both sides of these
A+2&U
d U ]bYf
ionisation boundaries in very young
Hii regions
aimsYgto quantify the relationship between the Hii regions and their
immediate environments. We present high-resolution (∼ 0.5′′ ) ALMA observations of nine Hii regions selected from
:L<: . Al aUd
̶“
the Red MSX Source (RMS) survey with compact radio emission and bolometric luminosities greater than 104 L⊙ .
We focus on the initial presentation of the
ﬀ data, including initial results from the radio recombination line H29α, somecomplementary molecules, and the 256 GHz continuum emission. Of the six (out of nine) regions with H29α detections,* ABB
caYgUek%
two appear to have cometary morphologies
with velocity”gradients
across”them, and two appear more spherical withf&YkY
XkbUa]
velocity gradients suggestive of Vh
infallingionisedgas.f The remaining two were either observed at low resolution or
had signals that were too weak to draw robust conclusions. We also present a description of the interactions between+ ABB
A+2&U d U
the ionised and molecular gas (as traced by CS (J=5-4)), often (but not always) finding the Hii region had clearedz Of our sample of nine, the observations of the two clusters expected to haveits immediate vicinity of molecules.
the youngest Hii regions (from, previous
are suggestive of having infalling motions in the H29α
H PKHfradio observations)ABBemission, which could be indicative of late stage accretion onto the stars despite the presence of an Hii region.
ﬂAccepted by A&A
y
A&A proofs: manuscript no. EYH_Internal

P.D. Klaassen et al: The evolution of young Hii regions

Fig. 3: Continuum, H29↵, and CS emission from G336.98. The top left panel shows the 256 GHz continuum in colour scwhich the 5 GHz emission is shown in red contours; the red contours in the other images represent this same 5 GHz emissio
comparison. The yellow contours show the outlines of the FellWalker identified cores. The bottom left panel shows theemission (black) with its Gaussian fit. The grey line shows the residuals from the Gaussian fit. In these spectra, the emissio
been recentred to the expected rest velocity of the source, thus the velocity shift of the line peak (from zero) represents a di↵ebetween the ionised and molecular gas velocities. The top two panels on the right show the moment 0 and moment 1 maps
H29↵ emission (top and bottom), while the bottom two panels on the right show the moment 0 and moment 1 maps of themission (top and bottom).

Fig. 2: Continuum, H29↵, and CS emission from G330.28. The top left panel shows the 256 GHz continuum in colour scale inwhich the 5 GHz emission is shown in red contours; the red contours in the other images represent this same 5 GHz emission forcomparison. The yellow contours show the outlines of the FellWalker identified cores. The bottom left panel shows the H29↵
emission (black) with its Gaussian fit. The grey line shows the residuals from the Gaussian fit. In these spectra, the emission has
been recentred to the expected rest velocity of the source, thus the velocity shift of the line peak (from zero) represents a di↵erence
between the ionised and molecular gas velocities. The top two panels on the right show the moment 0 and moment 1 maps of the
H29↵ emission (top and bottom), while the bottom two panels on the right show the moment 0 and moment 1 maps of the CS
emission (top and bottom). .

Article number, page 10 of 25

Article number, page 9 of 25

https://arxiv.org/pdf/1712.04735
- *aa

a

A<ABB
H bursty star cluster formation:
Evidence for feedback and stellar-dynamicallyregulatedthe case of the Orion Nebula Cluster
23
45
Pavel Kroupa1,6 , Tereza Jerabkova. A+2U d , UFrantisek Dinnbier]bZU , Giacomo Beccari and Zhiqiang Yan
1Bonn University, Germany; 2 ESO, Garching, Germany; %3 IN
Cologne University, Germany; 4 ESO, Garching, Germany;

Table 7: Derived HII region properties based on H29↵ emission. Temperatures derived assuming line widths are thermal,
and voigt profile widths are taken to be the greater of half thechannel width (0.25 km s 1 ) or the uncertainty on the Gaussian
fit in Table 6.
I “ H
Target

T
(K)
2800
3300
4100
1900
1500
4100

vp
(km s 1 )
0.25
1.8
0.25
0.54
1.4
0.25

ne
(107 cm 3 )
<1.5
<11
s<1.5
<3.0
<7.7
w<1.5

MHII
M
<38.4
<482.9<274.0<80.2<220.1<1206.7

Sc
(mJy)
11
2.3
8.7
2.7
3.4
1.9

gions is also curious. Two are the most chemically rich i
study (G339.11, and G336.98, which, from its radio SED
pected to be one of our youngest Hii regions), while the(G302.02) shows no molecular emission across the Hii r(neither in the H29↵ nor CS passbands), suggesting that theplex molecules have been destroyed by the ionising radiatio
3.3. Models of ionised gas

Peters et al. (2012) implemented the modelling of RRL line
files detectable at JVLA and ALMA wavelengths into RADM
using non-LTE methods to understand line shapes. The test
they used to demonstrate the code focussed on infalling andflowing RRL emission, and under which conditions these stures would be detectable.
These conditions require the observations of the opt/00
kZ2 >7A&A
7 proofs:A 7 manuscript
A D no. EYH_Internal
7D9c thick RRLs to be of high resolution and sensitivity, and fo
intrinsic line widths to be narrow enough for the asymmetr
S Jeans S
SDerivedlengths inlc
(given in au), and core separation
statistics, including the mean and standard deviation ( ) of thespectrally(e.g.forpressure
broadening does notrations.
Generally,
the Jeanslength (Lis resolvedin these
observations.
The
Turbulentresolved
Jeans Length,comparison,little tono emission
overlaps
with
Hii region
itself.
If the be
Jeans )ther Hii
60000.0
AU.is pushing through the ambient material, this o↵set is inate the spectrum). In Figure 14 of Peters et al., these au
regionlikely due to the molecular gas having been compressed at the outlined the parameter space in which line profile variationof position
canSep.
be attributed to dynamics, and findNo. clumps
LJeans
Sep.
Sep. function
L Jeans /Mean
Sep. Max
headTargetof the cometary
region,whichMean
leavesa cavity in itsMinwake.
space in the top
right of their figure where RRL emi
G302.02
13 by expansion
18740
6500 then5000
1.05
27400
If theo↵set is causedof17900
the Hii region,
it is rameteris opticallythe medium thermally supported, thG302.48
11
18740 where
12900
6800
5700
1.45 thick and28200
a productof the density
gradient,
one edgeof the region
G309.89
12 compressing)
18740 the22600
9900 while
12500
0.83high frequency
40300observations of the densest Hii reg
pushesagainst (anddense material
the requiring
73
Our
observations
(⌫
⇠
256
GHz,
n
<
5
⇥
10
cm
) fal
G330.28
7
20772
27400
13800
10800
0.76
50900
e
other edge is able to break out of the ambient gas and push out
G332.77
2
18740
38700
0
38700
0.48
this parameter
space,38700
and indeed, we do find these line asym
the lessdensematerial
asitexpands.
G336.98
4
12867
11200
5300
7000
18600
tries in1.15
some of our regions.
For two of our7targets, 22286(G302.02 9100
and G336.98,
G337.63
5000and poten3000
17600 for infalling gas as traced by H
We2.45
reran their models
tiallyG339.11, but9at lower18740
resolution),
the RRL
shows a4600
conG337.84
13400
7500
1.40
These
model results25400
are shown in Figure 10, where we pr
A&A
proofs:manuscript
no.
EYH_Internal
centric
velocity gradient,theso-called‘bulls-eye’morphology
G339.11
5
15838
27200
10900
15100
0.58
40100
the zeroth and first moment maps along with normalised(see, for instance, Sollins et al. 2005). Similar (e.g. redshifted
tra taken
at radialalong
the opticallyto thethin tr
Table 4: Derived Jeans lengths (given in au), and core separation statistics,
includingthepoints
mean andstandard
deviationthick( ) oftowards
the centre) profiles were predicted for optically thickcore separations. Generally, the Jeans length (LJeans ) is resolved in theseobservations.
Turbulent
Jeans Length,
for comparison,tion(outwards).The
The
first momentmap clearlyshows red-sh
RRL
emissionininfallingHiiregionsbyPetersetal.
(2012,
seeRadio is(5ofGHz)of eachorderflux
60000.0
AU.Hii region and spectral ↵An estimate of
the free-freeemissioncan beemissionin thecontinuum
optically thickregion.
Because the emissi
Section3.3),
suggestingthesevelocity
gradients
areconsistentfrom Urquhart et al. (2014)). The total flux from theG302.02
G330.28
G336.98
G337.63G337.84
G339.11

&

The Magellanic Bridge cluster NGC 796: Deep optical AO imaging reveals the stellar
content and initial mass function of a massive open cluster
Venu M. Kalari1 , Giovanni Carraro2 , Christopher J. Evans3 and Monica Rubio1
1

Departamento de Astronomia, Universidad de Chile, Casilla 36-D, Santiago, Chile; 2 Dipartimento di Fisica e
8
Astronomia Galileo Galilei, Vicolo Osservatorio 3, I-35122, Padova, Italy; 3 UK Astronomy Technology Centre, Royal
Observatory Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK
E-mail contact: venukalari at gmail.com
NGC 796 is a massive young cluster located 59 kpc from us in the diﬀuse intergalactic medium of the 1/5–1/10 Z⊙
Magellanic Bridge, allowing to probe variations in star formation and stellar evolution processes as a function of
metallicity in a resolved fashion, providing a link between resolved studies of nearby solar-metallicity and unresolved
distant metal-poor clusters located in high-redshift galaxies. In this paper, we present adaptive optics griHα imaging
of NGC 796 (at 0.5′′ , which is ∼ 0.14 pc at the cluster distance) along with optical spectroscopy of two bright members
to quantify the cluster properties. Our aim is to explore if star formation and stellar evolution varies as a functionof metallicity by comparing the properties of NGC 796 to higher metallicity clusters. We find from isochronal fittingof the cluster main sequence in the colour-magnitude diagram an age of 20+12−5 Myr. Based on the cluster luminosity
function, we derive a top-heavy stellar initial mass function (IMF) with a slope α = 1.99±0.2, hinting at an metallicity
and/or environmental dependence of the IMF which may lead to a top-heavy IMF in the early Universe. Study ofthe Hα emission line stars reveals that Classical Be stars constitute a higher fraction of the total B-type stars whencompared with similar clusters at greater metallicity, providing some support to the chemically homogeneous theoryof stellar evolution. Overall, NGC 796 has a total estimated mass of 990±200 M⊙ , and a core radius of 1.4±0.3 pc
which classifies it as a massive young open cluster, unique in the diﬀuse interstellar medium of the Magellanic Bridge.
Accepted by ApJ
https://arxiv.org/pdf/1801.01490

ALMA observations of the narrow HR 4796A debris ring
Grant M. Kennedy1 , Sebastian Marino2 , Luca Matrá3 , Olja Panić4 , David Wilner3 , Mark C. Wyatt2 ,Ben Yelverton2
1

Department of Physics, University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL, UK; 2 Institute of Astronomy,
University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK; 3 Harvard-Smithsonian Center for Astrophysics,
60 Garden Street, Cambridge, MA 02138, USA; 4 School of Physics and Astronomy, University of Leeds, Leeds LS2
9JT, UKFig. 10.— Stellar IMF of NGC 796 in logarithmic mass, with thebest-fit slope of ↵ = 1.99 for the 1.5-10 M range. The slope for a
Salpeter IMF (↵ = 2.35) is also shown.

= 1.99 ± 0.2= 2.35
3.5

3.0

10 M

1.5 M

log (M)the fraction of cBe stars relative to all known B spectral type stars in 21 clusters in the SMC (at 1/5 Z ),2.5
LMC (1/2 Z ) and the Galaxy. They found that thefraction of cBe stars increases with decreasing metallic2.0
ity (although they only studied one cluster in the SMC).
The results of Maeder et al. (1999) advocate the possibility of faster rotation at lower metallicities, which is a
1.5
0.2
0.4
0.6
0.8
1.0
key component of the chemically-homogeneous evolutionlog M (M )theoryFig.
at11.—
lower
metallicities.
studiesHalf mass
radius vs. clusterFurther
mass diagram.
NGC 796by MarFig. 10.— Stellar IMF of NGC 796 in logarithmic mass, with the(red circle) is plotted in comparison with 20 Myr open clusters
est-fit slope of ↵ = 1.99 for the 1.5-10 M range. The slope fortayanaet al. 20(2010)
includingmultipleSMC
and(crosses),
Myr youngmassive clusters(YMCs; blue
circles),andGalactic
alpeter IMF (↵ = 2.35) is also shown.
OB associations(triangles)
from the theliterature(see textfrequency
for details).
clusters
foundthat
althoughaverageof cBeThe black asterisks denotes clusters in the Magellanic Bridge fromto B stars
increases
as a thanfunction
there
are further
Mackey etal. (2017) younger
100 Myr; ofand Z,
the blacksquares
he fraction of cBe stars relative to all known B specSMC open clusters younger than 100 Myr from Hunter et al. (2003)
to thepossiblyother
ral type stars in 21 clusters in the SMC (at 1/5 Z degeneracies),
and Maia etdueal. (2014).
Thecluster
green lineage,
denotesanda clusterwithMC (1/2 Z ) and the Galaxy. They found that theinitial density greater than 104 M pc 3 , and the blue line shows
factors.
raction of cBe stars increases with decreasing metallicthe dynamical timescale of 20 Myr. Lines of equal relaxation timeInFig.
6 shown
the (ri) black.
colour of members is plotted against
are also
in solidy (although they only studied one cluster in the SMC).
the (r47%,H↵)
colour,which
is aMartayan
measureof (2010)
the strength
The results of Maeder et al. (1999) advocate the possi50%,
and45%,
respectively.
etal.
ility of faster rotation at lower metallicities, which is ofa H↵ line emission, from which the H↵ emitters are easfound that at an age of 20 Myr, the average RcBe at theey component of the chemically-homogeneous evolution
SMC Z at B0-B3
spectral typesouris ⇠10%,considerably
ily identified.
On restricting
magnitude
range in r
heory at lower metallicities. Further studies by Marlower
than ourderived estimate.B0-B3
If the stars,
metallicity
of quanto only
includemain-sequence
we canayan et al. (2010) including multiple SMC and Galactic
NGC 796 were lower, it would extend the Z range of such
lusters found that although the average frequency of cBe
tify thefractionof earlytype
B starsis withH↵bothexcess as arelations;however
futurespectroscopy
requiredo B stars increases as a function of Z, there are further
fractionof the total
stars inand
NGC
796.
Given the clusto determine
stellarB
metallicies
verifythe candidate
egeneracies due to the cluster age, and possibly otheremission-linestars.
ter’s ageof ⇠ 20
Myr, the amount of H↵ excess and theactors.
In Fig. 6 the (r i) colour of members is plotted against
correlated near-infrared(H openKs)
excess, we are confi4.3. Massive
clusterhe (r H↵) colour, which is a measure of the strength
dent thatthese NGCstars796
arecBethestars.
The
ratio clusof cBe stars
To classify
withincontext
of knownf H↵ line emission, from which the H↵ emitters are easstarsit (R) in the radius
B0-B3
range wasters, we placein the(rhspectral) vs. Mcl diy identified. On restricting our magnitude range in tor (cBe+B)
cBehalf-mass
agram of toPortegies
Zwart et whereal. (2010)
in errorFig. 11. isHere,o only include main-sequence B0-B3 stars, we can quandetermined
be 37±6%,
thethe propa-