1#

1 

0 11

Core fragmentation and Toomre stability analysis of W3(H2 O)
A case study of the IRAM NOEMA large program CORE?
A. Ahmadi1, 2 , H. Beuther1 , J. C. Mottram1 , F. Bosco1, 2 , H. Linz1 , Th. Henning1 , J. M. Winters3 , R. Kuiper4 ,R. Pudritz5 , Á. Sánchez-Monge6 , E. Keto7 , M. Beltran8 , S. Bontemps9 , R. Cesaroni8 , T. Csengeri10 , S. Feng11 ,R. Galvan-Madrid12 , K. G. Johnston13 , P. Klaassen14 , S. Leurini15 , S. N. Longmore16 , S. Lumsden13 , L. T. Maud17 ,K. M. Menten10 , L. Moscadelli8 , F. Motte18 , A. Palau12 , T. Peters19 , S. E. Ragan20 , P. Schilke6 , J. S. Urquhart21 ,F. Wyrowski10 , and H. Zinnecker22, 23(Affiliations can be found after the references)

s r f
Wk O
7 Received;Rc fp I
Accepted(37( 73 OI
0344R
H E 5 Rs
N
ABSTRACT725. .
1 Context.(+?? ,4 .5 ( ? )( ? BC
D
The fragmentation mode of high-mass molecular clumps and the properties of the central rotating structures surrounding the mostrXiv:1808.00472v1 [astro-ph.GA] 1 Aug 2018

ØØ
Ø

A&A proofs: manuscript no. W3H2O_arXiv

luminous objects have yet to be comprehensively characterised.

A&A proofs: manuscript no. W3H2O_arXiv
Aims. We study the fragmentation and kinematics of the high-mass star-forming region W3(H2 O), as part of the IRAM NOEMA large program

CORE.

(+ ??

Methods. Using the IRAM NOrthern Extended Millimeter Array (NOEMA) and the IRAM 30-m telescope, the CORE survey has obtained high-I

resolution observations of 20 well-known highly luminous star-forming regions in the 1.37 mm wavelength regime in both line and dust continuum
emission.
00
Results. We present the spectral line setup of the CORE survey and a case study for W3(H( 2 O). At ⇠0 . 35 (700 AU at 2.0 kpc) resolution, theW3(H2 O) clump fragments into two cores (West and East), separated by ⇠2300 AU. Velocity shifts of a few km s 1 are observed in the dense-gas
tracer, CH3 CN, across both cores, consistent with rotation and perpendicular to the directions of two bipolar outflows, one emanating from eachcore. The kinematics of the rotating structure about W3(H2 O) W shows signs of di↵erential rotation of material, possibly in a disk-like object. The
observed rotational signature around W3(H2 O) E may be due to a disk-like object, an unresolved binary (or multiple) system, or a combinationof both. We fit the emission of CH3 CN (12K 11K ) K = 4 6 and derive a gas temperature map with a median temperature of ⇠165 K acrossW3(H2 O). We create a Toomre Q map to study the stability of the rotating structures against gravitational instability. The rotating structures appear
to be Toomre unstable close to their outer boundaries, with a possibility of further fragmentation in the di↵erentially-rotating core, W3(H2 O) W.
A. Ahmadi
et al.: Core fragmentation and Toomre stability analysis of W3(H2 O)
Rapid cooling in the Toomre-unstable regions supports the fragmentation
scenario.
Conclusions. Combining millimeter dust continuum and spectral line data toward the famous high-mass star-forming region W3(H2 O), we identify
core fragmentation on large scales, and indications for possible disk fragmentation on smaller spatial scales.

A<< A<<

Ø 2O

U07

07

M

Key words. stars: formation – stars: massive – stars: early-type – stars: kinematics and dynamics – stars: individual: W3(H2 O), W3(OH)–

Fig. 3. NOEMA 1.37 mm (219 GHz) continuum image toward W3(H2 O) and W3(OH)in the ABD
configuration. The solid contours start at 6
techniques:interferometricnd increase in steps of 6 (1 = 3.2 mJy beam 1 ). The dotted contours show the same negative levels. A scale-bar and the synthesized beam
00
00
0 . 43 ⇥ 0 . 32, PA=86 ) are shown in the bottom.

Ø ?
down to core scales (e.g., Bontemps et al. 2010; Palau et al. 2013,
Ø B m 1. Introduction
U2
2015; Beuther et al. 2018; see review by Motte et al. 2017), andFundamental questions pertaining to the fragmentation of high- disk fragmentation at smaller spatial scales (e.g., Matsumoto &mass clumps
accretion
processes that result in the birth Hanawa 2003; see review by Kratter & Lodato 2016).
eeand theàsof the most massive stars (M & 8 M ) still remain unanswered.
In the disk-mediated accretion scenario, the non-isotropicØs This is in epart due to the clustered nature of star-formation
treatment of the radiation field reduces the e↵ect of radiationand the typically large distances involved. For a long time,the existence of high-mass stars had been puzzling as it was pressure in the radial direction, such that radiation can escapethroughtheimagepolestowardalong the disk rotation axis, while the disk is
Fig. 7.
NOEMA would
1.37 mmpre(219 GHz)
continuum
thought that the expected intense radiationpressure
W3(H2 O) in grey with levels starting atshielded
6 and increasingin thestepshighofduetoObservationally, the existence
vent the accretion of enough material onto
protostar(e.g., to the cm emission from Wilner densities.
Fig. 6. Top left: Intensity map of CO (2–1) emission from IRAM 30-m integrated over the velocity range of 40 to 20 km s 1 for the redshifted
6 . Thethe
black
contours correspondCore fragmentation and Toomre stability analysis of W3(H2 O)
A case study of the IRAM NOEMA large program CORE?
A. Ahmadi1, 2 , H. Beuther1 , J. C. Mottram1 , F. Bosco1, 2 , H. Linz1 , Th. Henning1 , J. M. Winters3 , R. Kuiper4 ,R. Pudritz5 , Á. Sánchez-Monge6 , E. Keto7 , M. Beltran8 , S. Bontemps9 , R. Cesaroni8 , T. Csengeri10 , S. Feng11 ,R. Galvan-Madrid12 , K. G. Johnston13 , P. Klaassen14 , S. Leurini15 , S. N. Longmore16 , S. Lumsden13 , L. T. Maud17 ,K. M. Menten10 , L. Moscadelli8 , F. Motte18 , A. Palau12 , T. Peters19 , S. E. Ragan20 , P. Schilke6 , J. S. Urquhart21 ,F. Wyrowski10 , and H. Zinnecker22, 23

profiles do not

2

E

3

(Affiliations can be found after the references)

O

Ø
,
H
O
Ø N
ABSTRACTß N
HØO
Context. The fragmentation mode of high-mass molecular clumps and the properties of the central rotating structures surrounding the mostluminousàobjects have yet to be comprehensively characterised.
Ø A. Ahmadi et al.: Core
Ofragmentation and Toomre stabilityWanalysis of W3(H O)
Aims. We study the fragmentation and kinematics of the high-mass star-forming region W3(H O), as part of the IRAM NOEMA large program

rXiv:1808.00472v1 [astro-ph.GA] 1 Aug 2018ØØ
Ø NØToomre stability analysis
Cof W3(H O)
fragmentation andimage toward
sing in steps ofon from Wilnerrom Hachisuka
and red arrows
m Zapata et al.
e cm emission
left corner. The
hown in grey in

,

CORE.

Received; Accepted22

proofs: manuscript no. W3H2O_arXiv
Methods. Using theA&A
IRAM
NOrthern Extended Millimeter Array (NOEMA) and the IRAM 30-m telescope, the CORE survey has obtained high-resolution observations of 20 well-known highly luminous star-forming regions in the 1.37 mm wavelength regime in both line and dust continuum

olutions in other sources (e.g., Beltrán et al. 2005; Beuther et al.
emission.
2007).

Results. We present the spectral line setup of the CORE survey and a case study for W3(H2 O). At ⇠000. 35 (700 AU at 2.0 kpc) resolution, theW3(H2 O) clump fragments into two cores (West and East), separated by ⇠2300 AU. Velocity shifts of a few km s 1 are observed in the dense-gas
tracer, CH3 CN, across both cores, consistent with rotation and perpendicular to the directions of two bipolar outflows, one emanating from each
Although we see a smooth
gradient inof
CHtheacross structure about W3(H O) W shows signs of di↵erential rotation of material, possibly in a disk-like object. The
3 CNcore.velocity
The kinematics
rotating
2
the entire W3(H2 O) structure, the existence of (at least) two
observedrotationalsignaturearound W3(H2 O) E may be due to a disk-like object, an unresolved binary (or multiple) system, or a combination
cores within it as presented by our continuum results, and twoof both.
We analysis.
fit the emission
ofdataCH3 CN (12K 11K ) K = 4 6 and derive a gas temperature map with a median temperature of ⇠165 K acrosscollimated outflows requires
further
Imaging theW3(H2 O). Wea Toomrein the most extended configuration
andcreate
therefore
reaching Q
ourmap to study the stability of the rotating structures against gravitational instability. The rotating structures appear
highest resolution, we tocanbefilter
out theunstablelarge-scaleenvelope
to outer boundaries, with a possibility of further fragmentation in the di↵erentially-rotating core, W3(H2 O) W.
Toomreclose
to theiranalyse the kinematicsRapidof gas aroundeach
cores. Figure 9
cooling
in ofthetheToomre-unstableregions supports the fragmentation scenario.
shows the first moment map of CH3 CN (123 113 ) for the cores
Conclusions.
Combiningexclusively.
millimeter dust continuum and spectral line data toward the famous high-mass star-forming region W3(H2 O), we identify
to the east and west using
the A-array observations
core andfragmentationon large
scales, and indications for possible disk fragmentation on smaller spatial scales.
The maps have been scaled
masked to highlightthe velocity
4.1.2. Small-scale

structure of each core. The mean line-of-sight velocity di↵erence
Key W3(Hwords.
stars: formation – 1stars: massive – stars: early-type – stars: kinematics and dynamics – stars: individual: W3(H2 O), W3(OH)–between the two main cores,
2 O) W and E, is a few km s .
Velocity di↵erences oftechniques:a few km s 1interferometric
are observed across eachcore, approximately perpendicular to the directions of the bipolar molecular outflows emanating from each core (Zapata et al.
2011). This indicates that the small-scale gradients across eachindividual core are mostdue to rotation. The two line-of1.likely
Introduction
down to core scales (e.g., Bontemps et al. 2010; Palau et al. 2013,
sight velocity gradients are on the order of ⇠1000 km s 1 pc 1 ,2015; Beuther et al. 2018; see review by Motte et al. 2017), anddepending on the choicefor the extent questionsof the gradient,much
Fundamental
pertaining
to the fragmentation of high- disk fragmentation at smaller spatial scales (e.g., Matsumoto &faster than the rotational motion of 170 km s 1 pc 1 for the whole
clumpsand theaccretionof W3(H2 O) from the mass
ABD data.
Furthermore,
the directionsof processes that result in the birth
Hanawa 2003; see review by Kratter & Lodato 2016).
the velocity gradients observed
eachmassive
core are slightlyof the formoststarsinclined(M & 8 M ) still remain unanswered.
In the disk-mediated accretion scenario, the non-isotropic
with respect to the overall
the gasThiseast-west
is in motion
part ofdue
to onthelarger
clustered nature of star-formation
scales (Fig. 5), suggesting that the general rotation seen aroundtreatmentof the radiation field reduces the e↵ect of radiation
the from
typicallylarge rotation.
distances involved. For a long time,
the two cores may beandinherited
the large-scalepressure
inthe radial direction, such that radiation can escapeMeanwhile, the direction
the blueshifted
outflow
theofexistenceof(redshifted)
high-mass
starsFig.
had9. been
puzzlingasitwasIntensity-weighted peak velocity (first moment) map ofthroughthepoles along the disk rotation axis, while the disk isemanating from W3(HthoughtO)W
isalmostintheopposite
direction
CH
CN
(12
11
)
using
only
the
A-arrayobservations
andmasked2333
thatejected
the expected
intense radiationpressure
would preof thefrom
and W3(H2 O)due
E (botFig.
plotsObservationally,
along a cut in the directionof rotation as depicted by dashed lines in Fig. 9 for fragment to the east (left) and to theFig. 8. Position-velocity plots
ofblueshifted
W3(H2 O)(redshifted)
for a cut inoutflow
the directionof W3(H2 O) E. out to show contributions from W3(H2 O) W (top) shielded
to10.
thePosition-velocity
high densities.
the existence
vent theangles
accretion
enoughthe protostar(e.g.,
tom). Theontosolid contours
correspond to
the 1.37 mm continuum in theThis implies that the inclinationof the twoofrotating
struc-material

Core fragmentation and Toomre stability analysis of W3(H2 O)
A case study of the IRAM NOEMA large program CORE?

A&A proofs: manuscript no. W3H2O_arXivrXiv:1808.00472v1 [astro-ph.GA] 1 Aug 2018

A. Ahmadi1, 2 , H. Beuther1 , J. C. Mottram1 , F. Bosco1, 2 , H. Linz1 , Th. Henning1 , J. M. Winters3 , R. Kuiper4 ,R. Pudritz5 , Á. Sánchez-Monge6 , E. Keto7 , M. Beltran8 , S. Bontemps9 , R. Cesaroni8 , T. Csengeri10 , S. Feng11 ,R. Galvan-Madrid12 , K. G. Johnston13 , P. Klaassen14 , S. Leurini15 , S. N. Longmore16 , S. Lumsden13 , L. T. Maud17 ,K. M. Menten10 , L. Moscadelli8 , F. Motte18 , A. Palau12 , T. Peters19 , S. E. Ragan20 , P. Schilke6 , J. S. Urquhart21 ,F. Wyrowski10 , and H. Zinnecker22, 23(Affiliations can be found after the references)Ø - 1
e .K/33L1 Received;
i Accepted
.K ds
TKc
Ø 3
6
C
k
K
C
ABSTRACTof high-mass molecular clumps N
and the propertiesof the central rotating structures surrounding the mostØ 05 < Context.
*0 The-fragmentationr modeHo kluminous objects have yet to be comprehensively characterised.
We study the fragmentation and kinematics
star-forming region W3(H O), as part
Ø t Aims.
Q
Mof the high-mass
K>HENt
kof the IRAMMNOEMA large program
=
CORE.
2

Methods. Using the IRAM NOrthern Extended Millimeter Array (NOEMA) and the IRAM 30-m telescope, the CORE survey has obtained high-resolution observations of 20 well-known highly luminous star-forming regions in the 1.37 mm wavelength regime in both line and dust continuum
emission.
Results. We present the spectral line setup of the CORE survey and a case study for W3(H2 O). At ⇠000. 35 (700 AU at 2.0 kpc) resolution, theA.
Ahmadiet al.: Core fragmentation and Toomre stability analysis of W3(H2 O)AU. Velocity shifts of a few km s 1 are observed in the dense-gas
W3(H2 O) clump fragments into two cores (West and East), separated by ⇠2300
A. Ahmadi
et al.:
Coreoutflows,
fragmentation
and Toomre
stability
tracer, CH3 CN, across both cores, consistent with rotation and perpendicular to the directionsof twobipolarone emanatingfromeach analysis of W3(H2 O)
core. The kinematics of the rotating structure about W3(H2 O) W shows signs of di↵erential rotation of material, possibly in a disk-like object. The
is calculated via
observed rotational signature around W3(H2 O) E may be
to a disk-likeConversely,
object, an unresolved
binarythis(or criticalmultiple) system,
to duefragmentation.
values above
value or a combinationof both. We fit the emission of CH3 CN (12K 11K ) K = 4 6 and derive a gas temperature map with a median temperature of ⇠165 K acrossS⌫ R
would put a marginally stable disk into a self-regulating scenario
NH2 =, W3(H2 O). We create a Toomre Q map(3)to study the stabilityof the rotating structures against gravitational instability. The rotating structures appear
B⌫ (T D ) ✓B ⌫ µ mH
suchathatheatingofacts
as afragmentation
stabilizing force
directly counter- core, W3(H O) W.
to be Toomre unstable close to their outer boundaries, withpossibility
furtherin theanddi↵erentially-rotating
2
acts
the
coolingrate.
Rapid cooling in the Toomre-unstable regions supports the fragmentation scenario.
where S ⌫ is the peak intensity,
✓
is
the
beam
solid
angle,µis
The Gammie
cooling
is relevant
only if the
diskW3(His 2 O), we identify
B
Conclusions.
Combining millimeter dust continuum and spectralline data toward
thecriterion
famous high-massstar-forming
regionthe mean molecular weight assumed
to be equal
2.8,scales,and mmarginallywith regions
thatspatial
are locally
H indications for possible
core fragmentation
on to
large
and
disk stable,
fragmentation
on smallerscales. unstable against

m

3

6

t

is the mass of the hydrogen atom. At a temperature of 140 K andaxisymmetric gravitational instabilities. A Toomre-stable diskstars: formationstars: massive – stars: early-type – stars: kinematics and dynamics – stars: individual: W3(H2 O), W3(OH)–using our continuum intensityKeyof awords.
given position
near the– cenwill not fragment regardless of how quickly it may be cooling.
techniques: interferometric 24
ter, we can estimate the H2 column
density to be 4.5 ⇥ 10 cm 2 .
This critical value is determined through numerical simulaThis can be converted to a volume density of nH2 > 7⇥107 cm 3 ,tions and varies depending on the heating and cooling recipes
assuming the extent of the third dimension to be at maximum theand convergence issues. For an overview of these issues, see
Introduction
to core(e.g., Bontemps
2010; Palau et al. 2013,plane-of-sky size of the clump1.(⇠4000
AU). Therefore, since theKratter & Lodatodown(2016),and scales
more recently
Baehr etetal.al.(2017).
2015;
Beuther
et
al.
2018;
see
reviewbydensity of molecular hydrogen is much higher than the critical
Regardlessof the specific numerical simulation issues, it isMottegen- et al. 2017), andFundamental questions pertaining to the fragmentationof highdiskthefragmentation
at ranges
smallerbetween
spatial scales(e.g., Matsumoto &density of the lines, the LTE assumption is valid and the rotaerally
assumedthat
criticalvalue
1
5.
mass clumps and the accretion processes that result in the birth Hanawa 2003; see review by Kratter & Lodato 2016).
tional temperature map of CH3 CN obtained from our modelling
FollowingtheprescriptionofKlassenetal.
(2016),of the most massive stars (M & 8 M ) still remain unanswered.
can be assumed to be tracing the gas kinetic temperature.
In the disk-mediated accretion scenario, the non-isotropic
This is in part due to the clustered nature of star-formation
Ez
Using Eq. 2, our continuum
map
with
its
unit
converted
treatmentof the radiation field reduces the(9)e↵ect of radiationt=,
and the typically large distances involved.
For coolingaQ
longFig. 12. Toomre
maptime,by assuming
tworadial
disk-likestructures
Fobtained
to Jy pixel 1 and the temperature
map obtained
from xclass,greypressure
in thedirection,such that radiation
can escapethe existenceof high-massstars hadinbeen
puzzlingas
itwasFig. 13. Map of cooling parameter obtained by assuming two diskgravito-centrifugal rotation about
the positions
ofalongpeak thecontinuum
assuming dust and gas temperaturesarecoupled,weobtainathrough
the
poles
disk
rotation
axis,
while
the disk isthought that the expected intense radiationpressurewould
prewhereEzthe
is twothe stars,
columnenergyemissionas depictedbyeach internalwith a massof 10 integrated
M . The in the z- like structures in gravito-centrifugal rotation about the positions of peak
pixel-by-pixel
mass density
map
(see
Fig.
C.1
in
AppendixC).
shielded
due
to
the
high
densities.
Observationally,
theexistence
Fig. 11. Column
density(top left),velocityo↵set(top
middle),
full
width
at
half
maximum
linewidth(topright),
androtationaltemperatureemission as depictedby stars. The(bottom
solid contours correspondvent the accretion of enough material
onto Q
thecalculations
protostar(e.g.,
Toomrethe positions(proto)stars
based
directionand(alongthe axisofof
rotation),areandF on theis the radiative continuum

Revisiting the case of R Monocerotis: Is CO removed at
R < 20 au?⋆T. Alonso-Albi1 , P. Riviere-Marichalar2 , A. Fuente1 , S. Pacheco-Vázquez1 , B. Montesinos3 , R. Bachiller1 , and S. P.
Treviño-Morales2, 4
1

Ø
Ø

3=

l

d
r aU amgaby il d
UEANISoV
0E - MC127 July 2017 / Accepted( k+ A
Received
20 May 2018
t- 8 0 Vc cUmnarXiv:1807.01893v1 [astro-ph.SR] 5 Jul 2018Øo
Ø IAPE 0 ko
Ø 8L 4ENB
Ø

Observatorio Astronómico Nacional (IGN), Calle Alfonso XII, 3, 28014 Madrid, Spaine-mail: t.alonso@oan.es,a.fuente@oan.es
2
Instituto de Ciencia de Materiales de Madrid (ICMM-CSIC). E-28049, Cantoblanco, Madrid, Spain.
T. et al. 2018: Re-visiting the case of R Mon
Alonso-Albi, T. et al. 2018: Re-visiting the case of R Mon
e-mail:Alonso-Albi,
pablo.riviere@csic.es
Alonso-Albi, T. et al. 2018: Re-visiting the case of R Mon
3
Departamento de Astrofísica, Centro de Astrobiología (CAB, CSIC-INTA), ESAC Campus, Camino Bajo del Castillo s/n, E-28692
Villanueva de la Cañada, Madrid, Spain.
4
Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden.

ABSTRACTV

8
i IAPE 0

(

lU

A
i r

-8
V

V

Context. To our knowledge, R Mon is the only B0 star in which a gaseous Keplerian disk has been detected. However, there is some
controversy about the spectral type of R Mon.)Some authors propose that it could be a later B8e star, where disks are more common.
Aims. Our goal is to re-evaluate the R Mon spectral type and characterize its protoplanetary disk.
Methods. The spectral type of R Mon has been re-evaluated using the available continuum data and UVES emission lines. We used a
A&A proofs: manuscript
no. 31658corr
power-lawdisk model to fit previous 12 CO 1→0 and 2→1 interferometric observations and the PACS CO data to investigate the disk
structure. Interferometric detections of 13 CO J=1→0, HCO+ 1→0, and CN 1→0 lines using the IRAM Plateau de Bure Interferometer(PdBI) are presented. The HCN 1→0 line was not detected.
Results. Our analysis confirms that R Mon is a B0 star. The disk model compatible with the 12 CO 1→0 and 2→1 interferometricobservations falls short of predicting the observed fluxes of the 14<Ju <31 PACS lines; this is consistent with the scenario in whichsome contribution to these lines is coming from a warm envelope and/or UV-illuminated outflow walls. More interestingly, the upper
limits to the fluxes of the Ju >31 CO lines suggest the existence of a region empty of CO at R!20 au in the proto-planetary disk. The
intense emission of the HCO+ and CN lines shows the strong influence of UV photons on gas chemistry.
Conclusions. The observations gathered in this paper are consistent with the presence of a transition disk with a cavity of Rin "20 au
around R Mon. This size is similar to the photoevaporation radius that supports the interpretation that UV photoevaporation is main
disk dispersal mechanism in massive stars

7
m

/1= 1
m pU

.

PL )
D05 1
r n
V

(

1

41 41
V

) HJ OT

Key words. circumstellar matter – stars: emission-line, Be – stars: formation

0- 0( 00disks around some Herbig Be stars exist at optical, near-infrared

1. Introduction(NIR),
mid-IR
wavelengths(Meeuset al.diﬀerent
2001; Vink
et for
al. the stellar parameters and extinction. The green line indicate
Fig. 5.
5.andFit
to thetheand
UBVRI
and
JHK
photometry
assuming
valuesFig. 5. Fit to the UBVRI andJHK photometry
diﬀerent values
for the stellar
parameters
extinction.
Theandgreen
line
indicates
the
Fig.
Fit
to
UBVRI
JHK
photometry
assuming
diﬀerent values
for thestellar parameters and extinction. The green line indicates
HerbigAe/Be starsassuming
are intermediate
mass (M∼2–8
M⊙ ) pre-main
2002;
Millan-Gabet
et
al.
2001;
Acke
et
al.
2005),
butthe
directstellarphotosphericemissioncorrected
forextinction.
The
red
line
is
the
dust
thermalemission
emissioncoming
coming
from
disk.
The
gray
line
is thesu
stellar photospheric emissionsequencecorrectedobjects.
for extinction.
The
red
line
is
the
dust
thermalemissioncoming
from
the
disk.
The
gray
line
is
the
sum
of
R
R
stellarphotospheric emission corrected for extinction.
The red line is the dust thermal
fromthethe
disk.
The
gray
line
is thesum
These objects share many characteristics
withboth contributions.
contributions.
detection of the disks at millimeter wavelengths remains eluboth contributions.
bothhigh-mass stars such as clustering and the existence of photo-Ø =32lt=M V r g0Eo ‒.) su
a .+V 0 5oVsive with only a handfulof detectionsk(Alonso-AlbiV0et al. 2009). l R.,kØ
5n dissociation regions (PDRs)vnk=M
m aVà
.+l0
e vV
in their surroundings, but their study Since the disk isR optically thick at NIR and mid-IR wavelengths,
Table
3.
Fitting
resultsfortheCOemissionTable
3. Fitting
CO emission
theforCOthelines.
Inour
ourapproximation,
approximation,thethegasgastemperaturetemperatureandanddenden- Table 3. Fitting results for the CO emission
presents antheimportant
advantage:
many
locatedresults
the CO lines.
In our approximation,
gas temperatureand thereden- aretheCOlines.
In
millimeter
observations are required
to estimate the dust
and gasØk
r0V closer
sity
aredescribed
bythepower-law
profiles
T
=
T
×
(R
/R)
to the Sun profiles(d ≤ 1 Kpc)
regionssity are described by the power-law
T =andT in× (R/R) less, complex than massive
sity are described by the power-law profiles T = T × (R /R) , ,
−p

q
K
in
in q
K
in
in observations
mass in the disk. On the other hand, spectroscopic−pΣ ∝ r−p . Even in this simple approximation the number of pastar forming
regions.theThenumberdetection. Even in this simple
approximationof andpa- detailed study of circum-

K

in

in

q

Σ ∝ r
Σ ∝ r of. Evenin thislines
simpleapproximation
the disk
numberof pamolecular
are usefulto study the
dynamics.
rameters isisFlat
too large
largetotobe
befitted
fittedonly
onlywith
withthetheCO
COobservations.
observations.
diskaroundAe/Be stars could provide valuable
rameters is too large to bestellar
fitted disks
only with
theHerbig
CO observations.
rameters
tooMonmassmass(M(M)
Thus,
wefixedfixed
someofofthe
theparameters
based
onthosethose
previously
Mon mass)
8±1
understandformation of Rmassive
stars.(M⊙Thus,
RRMon
Observations
ofparametersdisks havebased
been oncarriedoutusing the PhoThus, we fixed some of theinformation
parameterstobasedon thosethepreviously
wesome
previously
⊙ )⊙
◦

Flat
disk
Flat
disk
8±1
8±1

Revisiting the case of R Monocerotis: Is CO removed at
R < 20 au?⋆nt values for the stellar parameters and extinction.
The green1 line
indicates the 2 , A. Fuente1 , S. Pacheco-Vázquez1 , B. Montesinos3 , R. Bachiller1 , and S. P.
T. Alonso-Albi, P. Riviere-Marichalar
e is the dust thermal emission coming from the disk. The gray line is the sum ofTreviño-Morales2, 41bObservatorio Astronómico Nacional (IGN), Calle Alfonso XII, 3, 28014 Madrid, Spaine-mail: t.alonso@oan.es,a.fuente@oan.es
Table 3. Fitting results for the CO emission
2
Instituto de Ciencia de Materiales de Madrid (ICMM-CSIC). E-28049, Cantoblanco, Madrid, Spain.

arXiv:1807.01893v1 [astro-ph.SR] 5 Jul 2018

denØ
l
xsy
unrtT O J DHB 0- - .1 T
e-mail: pablo.riviere@csic.es A&A proofs: manuscript no. 31658corr/R)q ,
3
Departamento de Astrofísica, Centro de Astrobiología (CAB, CSIC-INTA), ESAC Campus, Camino Bajo del Castillo s/n, E-28692
f paVillanueva de la Cañada, Madrid, Spain.
Ø kl7- 9 CDBC 3~T
Flat disk 4 Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden.
ions.
R
Mon
mass
(M
)
8±1
ously
⊙
Received 27 July 2017 / Accepted 20 May 2018
Ø 3M V ) (
T
◦
i
(
)
20±10
.
ßo
U
b
T
ABSTRACT
Rout (au)1500
from
Rin (au)> 10 Context. To our knowledge, R Mon is the only B0 star in which a gaseous Keplerian disk has been detected. However, there is some
doptT in (K) (r = 1 au)
3400±500controversy about the spectral type of R Mon. Some authors propose that it could be a later B8e star, where disks are more common.
0 au,
Our goal is to re-evaluate the R Mon spectral type and characterize its protoplanetary disk.
Ø 3M,(h DHMT
q (T power-law index)
0.60±0.10Aims.
comMethods. The spectral type of R Mon has been re-evaluated using the available continuum data and UVES emission
lines. We used a
12
Mdisk (M⊙ )0.014±0.006
power-law disk model to fit previous CO 1→0 and 2→1 interferometric observations and the PACS CO data to investigate the disk
ue is
Ø
e l
- H
- >D + T
structure.
detections of 13 CO J=1→0, HCO+ 1→0, and CN 1→0 lines using the IRAM Plateau de Bure Interferometerp (Σ power-law index)
1.8±0.4 (PdBI) areInterferometriche J,
presented. The HCN 1→0 line was not detected.
cuzmf
t
ae iS
∆vturb (km/s)
0.5±0.3 Results. Our analysis confirms that R Mon is a B0 star. The disk model compatible with the 12 CO 1→0Øand 2→1 interferometricnewobservations falls short of predicting the observed fluxes of the 14<Ju <31 PACS lines; this is consistent with the scenario in whichdiskTsome contribution to these lines is coming from a warm envelope and/or UV-illuminated outflow walls. More interestingly,athe upper
limits to the fluxes of the Ju >31 CO lines suggest the existence of a region empty of CO at R!20 au in the proto-planetary disk. The
disk
R
E
c,
MT
intense emission of the HCO+ and CN lines shows the strong influence of UV photons on gas chemistry. Ø
midConclusions. The observations gathered in this paper are consistent with the presence of a transition disk with a cavity of Rin "20 au
Alonso-Albi,
T.
et
al.
2018:
Re-visiting
the
case
of
R
Mon
fit Thissimultaneously
eters disk. Using these parameters, we attemptedaroundRto
Mon.
size is similar to the photoevaporation radius that supports the interpretation that UV photoevaporation is main
Fig. 7. Comparison 12
between PACS observations and our radiative transfer model for diﬀerent values of the inner CO gap, and assuming a standard
disk
dispersal
mechanismin massiveCOabundance(1.6×10). The1→0
valuesfor Jandof 1 stars
and 2 are those found by Fuente et al. (2006).
ourpreviousinterferometricobservations
of
the
CO
m the
andcircumstellar
the PACS
data.
Key words.
matter– stars: emission-line, Be – stars: formation
Since 2→1 lines published by Fuente et al. (2006)
8. Discussion
12
etric The interferometric profiles of the CO 1→0 and 2→1 lines are
Planet formation occurs in protoplanetary disks during theearly stages of stellar evolution. These protoplanetary systems
around a 8±1 M⊙ starcan- best fitted assuming Keplerian rotation
evolve fromdisks
with a typicalratiostars exist
aroundsome gas-to-dust
Herbig Be
1. IntroductionØ
2massivedisksacat optical,
9 near-infrared- b
T−1of 100 to optically thin systems similar to our Kuiper Belt.
t the and a turbulent dispersion of 0.5±0.3 km s . The power-law(NIR),
mid-IR
wavelengths(Meeus et al. 2001; Vink et al.
The evolution of thedisk isandgovernedby viscoustransport
HerbigAe/Be stars(seeare intermediate
M⊙(Muzerolle) pre-main
et al. 1998)
and photoevaporation(Hollenbach
et al.b
2002;
Millan-Gabet
et al. 2001;
Acke et al. T
2005), but the direct
q=1.8±0.4
Table 3). mass
We (M∼2–8
Ø 70bà
imit, indexes are fited to p=0.60±0.1 and1994, 2000;
Clarke et al. 2001) and models combining both had
sequence objects. These objects share many characteristics
withdetection
of
the
disks
at
millimeter
wavelengths remains elubeen successfully used to explain the dispersal of protoplanetarynote that these are the only spectrally
resolved
line
profilesandhigh-mass stars such as clustering and the Ø
existenceof photodisks
around low-mass
TTS(Alexander
al.
the
with
only aethandful(Alonso-Albi et al.
2009).
DbutHDPDHB
AsiveMN
92006a,b).
-ofIndetectionsgib‒T
so-called
UV-switch model, evolution proceeds mostly throughdissociation
regions(PDRs)
intheirsurroundings,
their
study
then
the
only
information
about
the
kinematicaldisk
structure.
eters
disk
optically
viscous accretion toSincea point thewheremostisaccretion
stops.thick
From at NIR and mid-IR wavelengths,presents anon
importantadvantage:
many locatedcloserthis pointon, the gas
is quickly dispersedby photoevaporation.
4OJ
T.
h
MT
the 12 CO
1→0there
andare Ø
millimeter
observations
are required to estimate the dust andb
gas
aried The value of Rin has a neglible influence
Thismassive
is known as the two timescale problem. Also, planet forto the Sun (d ≤ 1 Kpc) and in regions less complex than
mass
in
the
disk.
On
the
other
hand,
spectroscopic
observations
is considered to play a major role in cleaning the inangularresolution
anddetailed study mation
ature 2→1 line profiles because of the limited
star forming
regions. The
detection andof circumner parts of the disk
the early evolution
systemsof inmolecularlines ofarethese
usefulto study the disk dynamics.
around Herbig Ae/Be stars could provide
valuable(Zhu
et al. 2012). To what extent the same mechanisms can be
m 1.0 sensitivity12 of our observations. stellar disks
13 CO model for line J=37→36,+ calculated for dif- used to explain the evolution of more massive Herbig Ae/Be
Fig. 8. Results of our
12

−4

u

understandtheandformation
re profile assumed in the CO model and for a second profileinformation
equal to half toof that.
CO, CN,HCO of massive stars.

Observations of disks have been carried out using the Pho-

The low mass population of the Vela OB2 association fromGaia

25 July 2018

JosephJ. Armstrong1 , Nicholas J. Wright1 and R. D. Je↵ries1
1
Astrophysics Group, Keele University, Keele, ST5 5BG, UK

ABSTRACTThe25 first
Gaia Data Release presents an opportunity to characterise the low-mass
July 2018
population of OB associations, providing larger statistical samples and better constraints on the formationABSTRACT
and evolution of clusters and associations. Using previously
The infirstaGaia
Dataregion
Release presents
opportunity
to characterise
the low-mass
known low mass members
smallof Velaan OB2
we havedesigned
selection
population of OB associations, providing larger statistical samples and better concriteria that combine Gaia
and
2MASS
independentlyof Using
any previously
astrometstraints
on theformationphotometry,and evolution of clusters
and associations.
knownlow-mass
low mass members
in a small region of Vela
OB2 wehave designed
selection
ric information, to identify
pre-main-sequence
(PMS)
stars
over thewider
criteria that combine Gaia and 2MASS photometry, independently of any astromet- 2
association area. Our method
pickstoout
thelow-mass
knownpre-main-sequence
clusters of youngstars
ric information,
identify(PMS) stars
overaroundthe wider2
association
area.
Our
method
picks
out
the
known
clusters
of
young
stars
aroundVelorum and NGC-2547, but also identifies other over-densities that may represent
Velorum and NGC-2547, but also identifies other over-densities that may represent
previously unknown clusters.
There
areclusters.
clearTheredi↵erencesin the inspatialdistributions
previously
unknown
are clear di↵erences
the spatial
distributions of ofthelow-massandthehigh-massOB
populations,suggesting
eitherthatthe structure
structure
the low-mass and the high-mass OB populations, suggesting either that theand dynamics of these populations has evolved separately or that the initial massand dynamics of these function
populations
has evolved separately or that the initial masscan vary considerably on small scales within a single association.
function can vary considerably
on small scales within a single association.
Key words: Surveys: Gaia, 2MASS; techniques: photometric; methods: data analysis:

arXiv:1807.09262v1 [astro-ph.SR] 24 Jul 201807.09262v1 [astro-ph.SR] 24 Jul 2018

1 Astrophysics Group, Keele University, Keele, ST5 5BG, UK

OB associations: Vela OB2

Key words: Surveys: Gaia, 2MASS; techniques: photometric; methods: data analysis:OB
4 associations:mm Vela OB2
o n
V O 24 4 7

l

V

P

Introduction

5 oi
eao
5
B
t
PG
S
F
V
Vr
N
M C

that high-density regions collapse to form bound clusters
while low-density regions disperse as unbound associations(Kruijssen 2012). To account for associations often being
OB associations are gravitationally unbound groups of OB
composed of smaller subgroups of di↵ering ages, Elmegreen
stars sharing a common motion through space (Blaauw& Lada(1977) proposeda sequential
formationmodelclusters
where
1 Introductionthathigh-density
regions
collapseto formbound1964). They make attractive subjects for studies of star foran ionization shock from newly formed OB stars is driven
mation and evolution due to their proximity
to regionsofwhile
low-density
as unboundassociations
intoregions
a moleculardisperse
cloud, compressing
material andtriggeringongoing star formation. Data from the Hipparcos satellite
a newgenerationof starformation.
This new groupof stars(Kruijssen2012).
Toaccountforassociations
often
being
(Perryman et groups
al. 1997) has
OB associations are gravitationally unboundof allowed
OB the study of the kinecan begin the process over again in a chain reaction, until
matics of bright stars in these associationscomposed(de Zeeuw et al.
of smaller
subgroups of di↵ering ages, Elmegreen
the cloud is dispersed and the association is left.
stars sharing a common motion throughspace(Blaauw
1999), but theseare only
the most massive members and a
An up-to-datepicture offormationa nearby association,& Lada (1977) proposeda sequential
modelmakwhereof thestellar1964). They make attractive subjectssmall
forfraction
studies
oftotalstar
for-population, assuming it foling use of the newest data to identify as much of its popionization
shock
from newly formed OB stars is driven
lows a classic Initial Mass Function (IMF).an
Much
is obscureulation as possible, may lead to a clearer understanding
mation and evolution due to their proximity
to regionsof stars in associations. To
about the populationof low-massinto a molecularofcloud,compressing
material
and oftriggering
association
evolution and thedeterminationa likely
do their positionsand velocities correlate withongoing star formation. Data from what
the extent
Hipparcos
satellite
formation scenario. Vela OB2 is an association at a mean
newgenerationof star formation. This new group of stars
those of the OB stars, how do they evolve,a andwhich
prodistance of 410 ± 12 pc, containing 93 OB stars based on(Perryman et al. 1997) has allowed cesses
the arestudyof thekineresponsible
for this
evolution?

4

1

+

V
24 4 7

V

+

B l
sBA
I
c

n

O
S
S
+ Fu

Tsuyoshi I NOUE , and Kengo TACHIHARA
1⇤

E-mail: doris.arzoumanian@nagoya-u.jp

Received ; Accepted

Abstract

arXiv:1807.08968v1 [astro-ph.GA] 24 Jul 2018

Department of Physics, Graduate School of
Science, Nagoya
University,
Furo-cho, and filament-cloud
Molecular
filament
formation
Chikusa-ku, Nagoya 464-8602, Japan
interaction:from d’Astrophysique,
Nobeyama 45m
2
Laboratoire AIM, CEA/DSM–CNRS–Universit
é Paris Diderot,Hints
IRFU/Service
C.E.A. Saclay, Orme des Merisiers, 91191telescope
Gif-sur-Yvette,observations
FranceDoris A RZOUMANIAN1 , Yoshito S HIMAJIRI2 , Shu-ichiro I NUTSUKA1 ,Tsuyoshi I NOUE1 , and Kengo TACHIHARA1
1

Department of Physics, Graduate School of Science, Nagoya University, Furo-cho,
Chikusa-ku, Nagoya 464-8602, Japan
2
Laboratoire AIM, CEA/DSM–CNRS–Université Paris Diderot, IRFU/Service d’Astrophysique,
18C.E.A.
13 Saclay, Orme12des Merisiers, 91191 Gif-sur-Yvette, Francex

We present Nobeyama 45m telescope C O, CO, and CO(1 0) mapping observationsc⇤E-mail: doris.arzoumanian@nagoya-u.jp
towards an interstellar filament in the Taurus molecular cloud. We investigate the gas velocity
Received ; Accepted
structure along the filament and in its surrounding parent cloud. The filament is detected in the
optically thin C18 O emission as a single velocity
component, ⇠ 1pc long, ⇠ 0.06pc wide structure.
Abstracts
13
The C18 O emission traces dust column densities
largerthan ⇠
5 ⇥telescope
1021 cmC218.O,The
line-of-sight
We present
Nobeyama
45m
CO,and 12 CO(1 0) mapping observations
interstellar
filament inamplitude
the Taurus molecular(LOS) velocity fluctuates along the filamenttowards
crestanwith
an averageof ⇠ 0.2cloud.
km sWe1 .investigate the gas velocity
6
structure along the filament and in its surrounding parent cloud. The filament is detected in the
13
12
The CO and CO integrated intensity maps
show spatially extended emission around theoptically thin C18 O emission as a single velocity component, ⇠ 1pc long, ⇠ 0.06pc wide structure.
elongated filament. We identify three extended
with dust
LOS
velocities
The C18structures
O emission traces
columndensitiesredshiftedlarger than ⇠and5 ⇥ 1021 cm 2 . The line-of-sightc
18(LOS) velocity
along
the filament
withBased
an average
blueshifted with respect to the average velocityof thefluctuatesfilament
identifiedin crest
C O.
on amplitude of ⇠ 0.2 km s 1 .
The 13 CO and 12 CO integrated intensity maps show spatially extended emission around the 2
combined analyses of velocity integrated channel
maps and intensity variations of the opticallyelongated filament. We identify three extended structures with LOS velocities redshifted and12thick CO spectra on and off the filament, blueshifted
we propose
a 3-dimensional
cloudwith respect
to the averagestructure
velocity of ofthethefilament
identified in C18 O.3O
Based oncombined
analysesofvelocity
integrated
channelmaps
andintensity
variationsofthesurrounding the filament. We further suggest a multi-interaction scenario where sheet-likem opticallythick 12 CO spectra on and off the filament, we propose a 3-dimensional structure of the cloud
extended structures interact, in space and surroundingtime, withthethe
filament and are responsible for its
filament. We further suggest a multi-interaction scenario where
6 sheet-likecompression and/or disruption, playing an extended
importantrole inthe starformationof theand are responsible for its
structuresinteract,in spaceand time, history
with the filament
3
compression
playing anshowing
important rolein the star formation
history of thefilament. We also identify, towards the same
field, and/ora verydisruption,
faint filamenta velocity
filament. We also identify, towards the same field, a very faint filament showing a velocity
field compatible with the filament formationfieldprocess
proposed by Inoue et al. (2017), wherecompatible with the filament formation process proposed by Inoue et al. (2017), wherea filament is formed due to convergence ofa afilament
flow isofformed
matterby ofthebendingtheduegenerated
to convergencea flowof matterofgenerated
by the bending of theambient
magnetic
field
structureinducedbyaninterstellar
shock
compression.
ambient magnetic field structure induced by an interstellar shock compression.

3 . 0
1 3
,
3
‒ 8
3
2
6
4

k
C

Key words: Stars: formation — ISM: clouds, filaments — Observations: dust and gas

Key words: Stars: formation — ISM: clouds, filaments — Observations: dust and gas
1 Introduction

3
. 3
5
p
c
4
2

Inutsuka et al. 2015). The typical timescale of such shock com-

6

C2

arXiv:1807.08103v1 [astro-ph.GA] 21 Jul 2018

Nahid Bahmani, Mohsen Nejad-Asghar
The eﬀect of magnetic field morphology on the structure of
Department of Physics, University of Mazandaran,massive
Babolsar,IRDC
Iran clumps
nejadasghar@umz.ac.ir Nahid Bahmani, Mohsen Nejad-Asghar
Department of Physics, University of Mazandaran, Babolsar, Iran

ABSTRACT

nejadasghar@umz.ac.iraD

ABSTRACTInfrared dark clouds (IRDCs) have dense elongated clumps andfilaments withR
the favorable viewing condition of being on the near-side of a bright mid-infrared
sx
Infrared dark clouds (IRDCs) have dense elongated clumps and filaments withbackground. The clumps usually have multiple
cores around the center. In thisthe favorable viewing condition of being on the near-side of a bright mid-infraredvo D
work, we study the eﬀect of magneticbackground.
field morphology
on the structure of masThe clumps usually have multiple cores around the center. In thisesxD
sive IRDC clumps. To achieve this goal,
weweconsider
axisymmetricisothermal
work,
study theaneﬀectof magnetic fieldmorphology on the structure of masc
IRDC clumps.
To achieve
this goal,
we consider
oblate IRDC clump, embedded into asiveconstantexternal
magnetic
field.
We as- an axisymmetric isothermal
oblate IRDC
clump,
embedded inside
into a constantexternal magnetic field. We assxtsume a polynomial function for the magnetic
fieldmorphology
the clump.
sume a polynomial function for the magnetic field morphology inside the clump.
We use the numerical iterative methods to solve the equations: the successive
sx v
We use the numerical iterative methods to solve the equations: the successive
over-relaxation method to find the magnetic
and method
gravitational
fluxes,andandthennuover-relaxation
to find themagnetic
gravitational x
fluxes, and thenthe bicongugate gradient method to findtheoptimized
valuesofmass
andcurrent
the bicongugate gradient method to find the optimized values of mass and current
densities.
The will
results
the IRDCalong
clumpthewill be very elongated along thedensities. The results show that the IRDC
clump
beshow
verythatelongatedsxD
Di
directionof theexternal
magnetic field lines. Also, the assumption
perpendicular direction of the externalperpendicularmagnetic fieldlines.
Also,
the assumptionof choosing of a polynomial function for the magnetic field morphology leads to rICr
of choosing of a polynomial function for the magnetic field morphology leads tothe formation of dense regions around the center. The greater the density of thelr
the formation of dense regions aroundcentral
the center.
The
greaterthe density
theregions and the closer to theregion, thelargerthe densityof these ofdenseD
central region, the larger the density center.
of thesedense
regions
andtheregions
closercan
to leadthe to the formation of cores at
The
presenceof these
dense
these points.
center. The presence of these dense regions
can lead to the formation of cores atthese points.
Subject headings: ISM: structure – ISM: clouds – ISM: magnetic fields – stars:
formation – (Galaxy:) local interstellar matter

Subject headings: ISM: structure – ISM: clouds – ISM: magnetic fields – stars:
formation – (Galaxy:) local interstellar matter
1.

Introduction

& Scientific Support Department, ESA ESTEC, Keplerlaan 1, 2200 AG Noordwijk, The Netherlands
Southern Observatory, Alonso de CÃşrdova 3107, Casilla 19001, Santiago, Chile

A sextet of clusters in the Vela OB2 region revealed by
Gaia?

XXX. Received YYY; in original form ZZZ
Giacomo Beccari,1 † Henri M.J. Boffin,1 Tereza Jerabkova,1,2,3 Nicholas J. Wright4 ,Venu
M. Kalari5 , Giovanni Carraro6 , Guido De Marchi7 and Willem-Jan de Wit8
1
European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München

2 Helmholtz Institut für Strahlen und Kernphysik, Universität Bonn, Nussallee 14–16, 53115 Bonn, Germany

Astronomical Institute, Charles University in Prague, V Holešovičkách 2, CZ-180 00 Praha 8, Czech Republic
ABSTRACT
34 Astrophysics Group, Keele University, Keele, ST5 5BG, UK

arXiv:1807.07073v1 [astro-ph.SR] 18 Jul 2018de Astronomia,
Universidad de with
Chile, Casilla
36-D, Correo Central, Santiago,
Chile
Using GaiaDepartamento
DR2 data,
combined
OmegaCAM
ground-based
optical photometry
Dipartimento di Fisica e Astronomia Galileo Galilei, Vicolo Osservatorio 3, I-35122, Padova, Italy
Research & ScientificSupport Department,
ESA ESTEC, Radial
Keplerlaan 1, 2200
AG Noordwijk,
The Netherlands
from the AD-HOC
survey,and detailed
Velocity
measurementsfrom ESO-Gaia,
European Southern Observatory, Alonso de CÃşrdova 3107, Casilla 19001, Santiago, Chile2
we analyse in detail a 10⇥5 deg region around the Wolf-Rayet star Vel, including thepreviouslyAcceptedknownclusters Gamma Vel and NGC2547. Using clustering analysis that
XXX. Received YYY; in original form ZZZ
considers positions, proper motions and parallax, we discover 6 clusters or associations
ABSTRACT of the colour-magnitude diagram for these clusters– 4 of which appear new. Analysis
Using Gaia DR2 data, combined with OmegaCAM ground-based optical photometry
show that 4 of them formed
coevally
fromthe samemolecular
10 Myr ago,from theAD-HOC survey,
and detailed
Radial Velocity
measurementsclouds
from ESO-Gaia,
we analyse in detail a 10⇥5 deg region around the Wolf-Rayet star 2 Vel, including thewhile NGC 2547 formed together
witha GammanewlyVeldiscoveredcluster
Myr
previously known
clusters
and NGC2547. Using
clustering 30
analysisthat ago. This
positions, proper motions and parallax, we discover 6 clusters or associations
study shows the incredibleconsiders
wealthof data provided by Gaia for the study of young– 4 of which appear new. Analysis of the colour-magnitude diagram for these clusters
show that 4 of them formed coevally from the same molecular clouds 10 Myr ago,stellar clusters.
while NGC 2547 formed together with a newly discovered cluster 30 Myr ago. This
5
6
7
8

study shows the incredible wealth of data provided by Gaia for the study of young

Stars: formation– Stars:– Openclusters andCasso4 4 0 Key
C words:
Sg
6stellar4 clusters.
-A 1pre-main
4 4 sequence
l
tDA
4
4 26
Key 26words: Stars:
Stars: pre-main sequenceciationsS
iWA3 7 04 6 ay formation – 56
N– Open clustersAand asso- e Arciations
A oC
M EO oV
D
SA o
R A
S Ed
C
R NS G N xD
m
1 INTRODUCTION
Gaia-ESO survey (GES Gilmore et al. 2012; Randich et al.
4 4 f Young clusters are a formidable tool to study star formation, 2013) found that the cluster around 2 Vel (namely Gamma

RODUCTION

Vel) is in fact composed of two coeval but kinematically
Gaia-ESO survey(GES Gilmore et al. 2012; Randich et al.
distinct populations A and B. Interestingly Sacco et al.
2 the(2015)
usedcluster
GES observations
to study
popu2013) found thatthearoundVelstellar(namelyGammalation on a region centered on NGC 2547, a ⇡35 Myr clus2 Vel. TheybutVel) is in fact tercomposedof south
twoof coeval
kinematicallylocated two degrees
find a population of stars whose RVs, lithium absorption lines, anddistinct populations
and B. Interestingly
Sacco et al.
positions in A
a colour-magnitude
diagram (CMD) are con-stellar evolution, binary stars, as well as the formation andevolution of clusters themselves. They thus o↵er a window
to observationally answer questions in many astrophysicaldomains. Hence, it is critical to discover and study as widea range of clusters as possible.
We recently concluded the Accretion Disk with OmegaCAM (ADHOC) survey on the VLT Survey Telescopesters are a formidable tool to study star formation,lution, binary stars, as well as the formation andof clusters themselves. They thus o↵er a window

sistent with those of Gamma Vel B, which they call NGC

10 1910 21 410 10 3 10 2 10 1 100 101 102 103 104

First Core Properties: From Low- to High-mass Star Formation
Radius [au]Asmita Bhandare1,4 , Rolf Kuiper2,1 , Thomas Henning1 , Christian Fendt1 , Gabriel-Dominique Marleau2,3,1 , and Anders
Kölligan2
1

Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
e-mail: bhandare@mpia.de
2
Institut für Astronomie und Astrophysik, Universität Tübingen, Auf der Morgenstelle 10, 72076 Tübingen, Germany
3
Physikalisches Institut, Universität Bern, Sidlerstr. 5, 3012 Bern, Switzerland
4
Member of the International Max-Planck Research School for Astronomy and Cosmic Physics at the University of Heidelberg(IMPRS-HD), Germany

2.5

(10)

d as adence onper limit(i.e. thes the sechowing

M

hn a
sSei

Ø . C6 FH =ABSTRACT=E9 = FD=B ,
2M
K 6F
K
Ømain goalK is to understandu cloudgo
Aims. In this study, thethe molecularcore collapse kthrough the stages of first and second hydrostatic
core formation. We investigate the properties of Larson’s first and second cores following the evolution of the molecular cloud core
until formation of Larson’s6F
cores. We expand thesecollapse studies
to span a wide range of initial cloud masses fromgok for the first timeM
0.5 to 100 M .
Methods. Understandingof the 9
numerous
involved in the9Every early stages ~Mof star formation
Ø the complexityC9
E= 9physical processes .=C=
requires detailed thermodynamical modeling in terms of radiation transport and phase transitions. For this we use a realistic gas

1.6

105

10 9

10 10
10

11

10 12

104

10 13
10 14
10 15

1

2

3

4

5

6

7

8

9 10

Ø 3+ 30-S
Ø 3+

1

C 4 + 6F 3 +
5- 4
4 3
H
3
S

form Larson’s second cores.

3
3 M
M

5.0
10 -1 Methods: numerical - Hydrodynamics - Radiative transfer - Gravitation - Equation of state
Key words. Stars: formation
4.5
3
10
10 8
10 9

Density [g cm 3]

1.8

1y
1.7

M

10 8

10 1
10 3
10 5
10 7
Radius [au]
10 9
10 11
equation of state via a density and temperature-dependent adiabatic index and mean molecular weight to model the phase transitions.
10 13
We use a gray treatment of radiative transfer coupled with hydrodynamics to simulate Larson’s collapse in spherical symmetry.
= 10 3 g cm 3
Results. We reveal a dependence of a variety of first core properties on the initial cloud mass. The first core radius and
10 15
K mass increase= 10 11 g cm 3
17from the low-mass to the intermediate-mass regime and decrease from the intermediate-mass to the high-mass regime. The lifetime10= 10 19 g cm 3of first cores strongly decreases towards the intermediate- and high-mass regime.
K
10 19
Conclusions. Our studies show the presence of a transition regionDin the intermediate-mass
regime. Low-mass protostars tend toD
21
10 3.5
1.5 2.0 2.5 3.0
4.0 4.5 0 5.01throughthe first
and manuscript
second hydrostaticcores. In contrast, in the highproofs:
no. 1Dcollapse
10 4 10 3 10 2 10 1evolve
10 10 102 103 two
104 distinct stages of formation which are related toA&A
mass[au]star formation regime, the collapsing cloud cores rapidly evolve through the first collapse
phase and essentially immediately
Radiuslog(T) [K]Radius [au]1

M

A&A proofs: manuscript no. 1Dcollapse

A&A proofs: manuscript no. 1Dcollapse

10 11

10 5
10 7
1. Introduction
Radius [au]
10 9
10 11
Stars are formed by the gravitational
collapse of dense, gaseous
10 13
and dusty cores within magnetized
15 molecular clouds. Details of
10
the earliest epochs of star formationand protostellar evolution
10 17
however remain far from fully understood
due to the complex19
10
ity of the physical processes involved,
such
as hydrodynamics,
10 21 4
3
3
radiative transfer and magnetic fields.
stars
10 10 Understanding
10 2 10 1 100 101how
102 10
104
10 12
10 13
10 14

4.0

H+

et al. 3.5
2012;
Tomida et al. 2013; Vaytet et al. 2013; Vaytet &H
Haugbølle
2017, and references therein) and smoothed particle
3.0
H2hydrodynamics(SPH) simulations (Whitehouse & Bate 2006;
1.4
2.5
Stamatellos et al. 2007; Bate et al. 2014) to better understand2.0
1.3
the isolated
collapse scenario. The early phases of low- andintermediate-massstar formation can briefly be summarized as
1.5
1.2= 10 3 g cm 3
follows.
1.0= 10 11 g cm 3
1.1
Initially, the optically thin cloud collapses isothermally un19
3
0.5
= 10
g cm
Radius[au]
10 the efficient
5
0 thermal emission fromform has thus been one of the most fundamental
questionsraised der its own20gravity15due to
1.0
3log (Density/ g cmThe) collapse may be initiated eithis phase.
for several
1.0 1.5 2.0 2.5 3.0 3.5 4.0
4.5 5.0decades (see detailed reviews by Larson 2003; Mc- dust grains during
Kee & Ostriker 2007; Inutsuka 2012). Owing to the optically ther by the ambipolar di↵usion of magnetic fields that once suplog(T) [K]portedthe12cloudagainst gravitational
collapse(e.g., Shu et al.
15
8 10
14 16182030
40
60
80 100thick regime, it is0.5still very challenging
to 2obtain reliable ob1987)
or
by
the
dissipationofturbulence
which
reduces the efInitial
cloud
mass
[M
]
servational
constraints
duringtheearliest
phasesofstarformaFig. 1: Mean molecular weight µ and adiabatic index
asfective speed of sound in cloud cores (e.g., Nakano 1998). It can
1.5

1

1 1

19

19

3+ 3
Initial profile
At first core formation
At second core formation

vhn

f

103
102

vhn

f

101

10 10

log (Temperature / K)ich takes
l degrees

0.5
1.0= CP /CV& Bodenof atomicgen (H2 )is a realwhere H2
ature andTO coderadiationarleau et1.0.

Density [g cm 3]e can be2012) foret al. (insection),radiation2011) for1.5cSubmitted: January 13, 2018 / Accepted: July 16, 2018

Density [g cm 3]

2.0µ

s (8) andation apevolve as
itionally,
he course

1

Density [g cm 3](9)rXiv:1807.06597v1 [astro-ph.SR] 17 Jul 2018

lution of

Rd

hlm
r

Temperature [K]Ø ‒ØLow- to High-mass Star Formation
S
Properties: From

10 15

1

2

3

4

5

6

7

8

9 10

10 4 10 3 10 2 10 1 100 101 102 103 104

Ø =CDE D BØcØ D9 B D B

Radius [au]

St M
St M
1x M

First Core Properties: From Low- to High-mass Star Formation
Asmita Bhandare1,4 , Rolf Kuiper2,1 , Thomas Henning1 , Christian Fendt1 , Gabriel-Dominique Marleau2,3,1 , and Anders
A&A proofs: manuscript no. 1Dcollapse
Kölligan2
1

Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
e-mail: bhandare@mpia.de
2
Institut für Astronomie und Astrophysik, Universität Tübingen, Auf der Morgenstelle 10, 72076 Tübingen, Germany
3
Physikalisches Institut, Universität Bern, Sidlerstr. 5, 3012 Bern, Switzerland
4
A&A proofs: manuscript no. 1Dcollapse
Member of the International Max-Planck Research School for Astronomy and Cosmic Physics at the University of Heidelberg(IMPRS-HD), Germany
12
Submitted: January 13, 2018 / Accepted: July 16, 2018

Ø 1
Ø

4
2
0

100

101

102

Initial cloud mass [M ]First core mass [M ]

0.10

0.08

0.06

0.04

0.02
100

101

Initial cloud mass [M ]1800
First core temperature [K]

1600
1400

102

1

S

2

1

dsr F
c‒
M

s

10

F
gF-+K L

Ø -+
àl à
F
Ø
S 3+o K
Ø
d
1
Ø
e K
2
n
F

ABSTRACT8
Aims. In this study, the main goal is to understand the molecular cloud core collapse through the stages of first and second hydrostatic
core formation. We investigate the properties of Larson’s first and second cores following the evolution of the molecular cloud core
6
until formation of Larson’s cores. We expand these collapse studies for the first time to span a wide range
D of initial cloud masses from
0.5 to 100 M .
4Methods.
Understanding the complexity of the numerous physical processes involved in the very early stages of star formation
requires detailed thermodynamical modeling in terms of radiation transport and phase transitions. For this we use= a realistic gas
equationof state via a density and temperature-dependent adiabatic index and mean molecular weight to model the phase transitions.
2
We use a gray treatment of radiative transfer coupled with hydrodynamics to simulate Larson’s collapse in spherical symmetry.
Results.
a dependence of a variety of first core properties on the initial cloud mass. The first core radius and mass increase
0 1 We reveal
1 intermediate-massfrom
to10the10 the low-mass
100
102
103 regime and decrease from the intermediate-mass to the high-mass regime. The lifetimeof first cores strongly
decreases
towards
the intermediate- and high-mass regime.
Time [years]
Conclusions. Our studies show the presence of a transition region in the intermediate-mass regime. Low-mass protostars tend to
Fig. 6: Time evolution of the first core radius showing an initial
evolve throughtwo distinct
stagesof formation
which are related to the first and second hydrostatic cores. In contrast, in the highcontraction
phase followed
by a rapid
expansionand a second
massformation
collapsingcloud
cores rapidly evolve through the first collapse phase and essentially immediately
contractiondi↵erentcloud
0.5 star1phase.
2 The colors
5 regime,
8 indicate
12 20thethe40
60 100 initial
A. Bhandare et al.: First Core Properties: From Low- to High-mass Star Formation
form ranging
Larson’s
secondcores.
masses
from
0.5
to
100
M
as
shown
in
the
color
bar.
Initial cloud mass [M ]First core radius [au]6Ø

Key words. Stars: formation - Methods: numerical10-3Hydrodynamics - Radiative transfer - Gravitation - Equation of stateFig. 6: Time evolution of the first core radius showing an initial
contraction
phasecorefollowedby a rapid
and spana second
the second
formation.
The expansion
vertical lines
the minimum
contraction
phase. The
indicateasthe
initial cloudto maximum
firstcolors
core radius
thedi↵erent
core evolves.
The transition
massesranging
from
0.5
to
100
M
as
shown
in
the
color
bar.
around 8 – 10 M is also seen for the first core mass (see Fig. 5b),

-+K
f
5

the second4core formation. The vertical lines span the minimum

M 0.5

1000

HF
t F

2

5C -0,y2

to maximum first core radius as the core evolves. The transition
0.5 (see Fig. 5b),around 8 – 10 M is also seen for the first core mass
2.5
1
whereas the first core temperature always increases with an increase in the initial cloud mass (see Fig. 5c).
800
The evolution of the first core radius from the onset of thefirst core formation until the second core formation is shown in0
600
Fig. 6. The first core undergoes an initial contraction phase fol0
lowed by a rapid expansion and a second contraction phase.
400
Figure 7 shows the onset of the first core formation as a func200
tion ofinitialcloud
mass. Inisthe
low-mass
range faster(M0 with
8 M the), first core
103 theregime,collapseseen
to be1much
dust grains
during thisphase. The collapse may be initiated ei0
forseveraldecades(seedetailed
Larson2003; Mcthe
cloudis seenundergoa comparatively
slowercollapse1
10 ( reviews
102 byfollowed
forming
aftertoa10
few thousandyears
5000 years)
by
100
101
102
100
102 di↵usion of magnetic fields that once suphence&
initiating
the first
core formation
after 2012).
⇡ 5000 - Owing
18000
ther by10the ambipolar
Kee
Ostriker
2007;
Inutsuka
totheopticallyaninstantaneous
secondcollapse
phase
which
prevents
thefirstInitial cloud mass [M ]Initialcloud
mass [Mand] high-mass
years. On the other hand,in theintermediateInitialported
cloud mass
] against gravitational collapse (e.g., Shu et al.
the [M
cloud
core
growing.
thick
regime,itis ischallenging
to obtain reliable obregime,
thefromcollapse
seenstill
to be verymuch fasterwith the first core
1987)
or
by
the
dissipation of turbulence which reduces the efforming
after
aof
few
thousand( 5000
years)
by of initial
Figure8formation
shows
the
first
core
lifetime
asfollowed
a function
Fig. 7: Onset
ofyears
the
first
core
for earliest
di↵erent
initialFig. 5: Dependence of the first core properties on initial cloudservational
constraints
duringthephasesofstarformaFig. 8: First core lifetime i.e. time between the onset of formationaninstantaneous
secondcollapse
phase
which
prevents
first
cloud
masses.
Initially
highermass
cloudstend
to collapse
cloud
mass.
The first
core
lifetimeisdefinedasthe
thefastertime between
mass. Shown is a) the mean first core radius (mean radius isfective speed of sound in cloud cores (e.g., Nakano 1998). It can

1200

L

HF

, , 2.,1 F

1
1. Introduction
et al. 2012; Tomida et al. 2013;Ø
Vaytet ,et al. 2013; Vaytet &10
whereas the first core temperature always increases with an increase in the initial cloud mass (see Fig. 5c).
Haugbølle 2017, and references therein) and smoothed particle
10
The evolution of the first core radius from the onset of the& Bate 2006;
Starsfirstareformedbyuntilthe thegravitational
collapse of dense, gaseous hydrodynamics (SPH) simulations (WhitehouseRF
core
formation
secondMcore formation is shown in
Stamatellos
et
al.
2007;
Bate
et
al.
2014)
to
betterunderstandMand dustycores
magnetizedclouds.
Fig. 6. The
first withincore undergoes
an initialmolecular
contraction phase
fol10 Details ofØtheisolatedcollapse
scenario.
The
earlyphasesoflow- a
and
lowed
by
a
rapid
expansionandasecondcontraction
phase.
the earliest epochs of star formation and protostellar evolution
intermediate-mass
starformationcanbrieflybesummarizedasFigure7 shows
onset ofthe first
core formation
as atofunchowever
remainfarthefrom
fully
understooddue
the complextion of initial cloud mass. In the low-mass range (M  8 M ),8=<
= 5follows.
ity ofthethe
physical
involved, suchhydrodynamics,
cloud
is seen toprocesses
undergo a comparatively
slowerascollapse
10
Initially,
theoptically
thin
cloud
collapses
isothermally
unradiative
andfields.
hence transfer
initiating thefirstmagnetic
core formation
afterUnderstanding⇡ 5000 - 18000 how stars
TF
On theotheronehand,
themostintermediateand high-mass
formyears.
has thus
been
ofinthefundamental
questions raised der its own gravity due to the efficient thermal emission fromOnset of first core formation [years]

8

First core lifetime [years]

10

rXiv:1807.06597v1 [astro-ph.SR] 17 Jul 2018

Mean first core radius [au]

12

L

K u
8ds

p

The Netherlands
Leiden Observatory, Leiden University, PO
BoxALMA-PILS
9513, 2300 RA Leiden,
The first
Netherlands
The
survey:detection of methyl isocyanide

9(CH3 NC) in a solar-type protostar

Received

H. Calcutt1 , M. R. Fiechter1, 2 , E. R. Willis3 , H. S. P. Müller4 , R. T. Garrod3 , J. K. Jørgensen1 , S. F. Wampfler5 , T. L.
Bourke6 , A. Coutens7 , M. N. Drozdovskaya5 , N. F. W. Ligterink8, 9 , L. E. Kristensen1
1

ABSTRACT

arXiv:1807.02909v1 [astro-ph.GA] 9 Jul 2018

Centre for Star and Planet Formation, Niels Bohr Institute & Natural History Museum of Denmark, University of Copenhagen,Øster Voldgade 5–7, DK-1350 Copenhagen K., Denmark, e-mail: calcutt@nbi.ku.dk
Universityof Groningen,
Nijenborgh
4, 9747number
AG, Groningen,
The Netherlands
Context. Methyl isocyanide (CH3 NC) is 23theisocyanide
withthe largestof atoms
confirmed in the interstellar medium (ISM),
Departments of Chemistry and Astronomy, University of Virginia, Charlottesville, VA 22904, USA4
but it is not an abundant molecule, having
only beenInstitut,
detected
towards
handful
its isomer, methyl cyanide
I. Physikalisches
Universität
zu Köln,aZülpicher
Str.of77, objects.
50937 Köln,Conversely,
Germany
5Center
for
Space
and
Habitability,
UniversityofBern,
Gesellschaftsstrasse
6,CH-3012Bern,
Switzerland(CH3 CN), is one of the most abundant 6complex organic molecules detected in the ISM, with detections in a variety of low- andSKA Organization, Jodrell Bank Observatory, Lower Withington, Macclesfield, Cheshire SK11 9DL, UK
high-mass sources.
7
Laboratoire d’Astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, allée Geo↵roy Saint-Hilaire, 33615 Pessac, France
8
RaymondBeverly Sacklerof
Laboratory
Astrophysics, Leiden
Observatory,
LeidenUniversity, PO binary
Box 9513,IRAS
2300 RA16293–
Leiden,Aims. The aims of this work are to determine
theandabundances
methylforisocyanide
in thesolar-type
protostellar
The Netherlands
2422 and understand the stark abundance9 Leidendi↵erences
observed
betweenmethylisocyanide
methyl cyanide in the ISM.
Observatory,
Leiden University,
PO Box9513, 2300
RA Leiden, and
The Netherlands

Methods. We use ALMA observations from the Protostellar Interferometric Line Survey (PILS) to search for methyl isocyanide andcompare its abundance with that of its isomer
methyl cyanide. We use a new line catalogue from the Cologne Database for Molecular
Received
Spectroscopy (CDMS) to identify methyl isocyanide lines. We also model the chemistry with an updated version of the three-phase
ABSTRACT
chemical kinetics model MAGICKAL, presenting the first chemical modelling of methyl
isocyanide to date.
Results. We detect methyl isocyanide forContext.
the first
time
in a solar-type
IRAS
16293–2422
B,confirmed
and present
upper medium
limits (ISM),
for its
Methylisocyanide(CH3 NC) is theprotostar,
isocyanide withthe largest
number of atoms
in the interstellar
is not an abundant
molecule,
onlytobeen
towardsa handfulof objects.
Conversely,isomer, B
methylcyanidecompanion protostar, IRAS 16293–2422but
A.it Methyl
isocyanide
ishaving
found
bedetected
at least
20 timesmoreabundant
in itssourcecompared(CH3 CN), is one of the most abundant complex organic molecules detected in the ISM, with detections in a variety of low- andto source A, with a CH3 CN/CH3 NC abundance
ratio of 200 in IRAS 16293–2422 B and >5517 in IRAS 16293–2422 A. We also
high-mass sources.
The aims ofisocyanide
this work are to chemistry
determine the abundances
methyl isocyanide
in the solar-typebinary IRAS
16293–
present the results of a chemical modelAims.
of methylin both ofsources,and discuss
the protostellar
implications
on methyl2422 and understand the stark abundance di↵erences observed between methyl isocyanide and methyl cyanide in the ISM.
isocyanide formation mechanisms and therelative
evolutionary
stagesofbothsources.
The
chemicalmodellingisunabletomatchtheMethods. We use ALMA observations from the Protostellar Interferometric Line Survey (PILS) to search for methyl isocyanide andobserved CH3 CN/CH3 NC abundance ratio
towards
the Bwithsourcedensities
oflinethatsource.
modelling,
compareits abundance
that of atits isomer
methylrepresentative
cyanide. We use a new
catalogue
fromThethe Cologne
Database however,for Molecularis
Spectroscopy(CDMS)
toidentify
methylisocyanidelines.
We
also
model
the
chemistrywithanupdatedversionof
thethree-phaseconsistent with the upper limits for the Achemicalsource.
There are many uncertainties in the formation and destruction pathways of
methylkinetics model MAGICKAL, presenting the first chemical modelling of methyl isocyanide to date.
isocyanide, and it is therefore not surprisingthattheinitialmodeling
attempts
donotreproduce
observations.
In
particular,
it
is
clear
Results. We detect methyl isocyanide for the first time in a solar-type protostar, IRAS 16293–2422 B, and present upper limits forits
companion
protostar,
IRAS
16293–2422
A.
Methylisocyanide
is
found
to
be
at
least
20
times
more
abundantinsourceBcomparedthat some destruction mechanism of methyl
isocyanide
which
does
not
destroy
methylcyanideisneeded.
Furthermore,these
initialto source A, with a CH3 CN/CH3 NC abundance ratio of 200 in IRAS 16293–2422 B and >5517 in IRAS 16293–2422 A. We alsomodel results suggest that the final density
plays
key ofrole
in setting
abundance
Theinnext
steps aretherefore
to obtain
present
the aresultsa chemical
modeltheof methyl
isocyanideratio.
chemistryboth sources,and discuss
the implications
on further
methyland the relative
evolutionary
stagesof both sources. The chemical
modelling
unable to matchdetections of methyl isocyanide in more isocyanide
objects,formation
as wellmechanisms
as undertaking
moredetailed
physico-chemical
modeling
ofissources
suchtheas
observed CH3 CN/CH3 NC abundance ratio towards the B source at densities representative of that source. The modelling, however, is
IRAS16293.
consistent with the upper limits for the A source. There are many uncertainties in the formation and destruction pathways of methyl
isocyanide, and it is therefore not surprising that the initial modeling attempts do not reproduce observations. In particular, it is clear

/ B2
HNM 3
3 9
B
4

AI
B
/
1 2
/ A
3
AR
4 -

0 -2
LP

/
C
LP 4
A
93 B A
S4
/ A
4 B
3 A
B 64
4

that some destructionof methyl
isocyanide
which does—
not ISM:
destroy individual
methyl cyanideobjects:
is needed. Furthermore,these initial
Key words. astrochemistry — stars: formation— stars:mechanism
protostars— ISM:
molecules
IRAS 16293–2422. Introduction

model results suggest that the final density plays a key role in setting the abundance ratio. The next steps are therefore to obtain further
detections of methyl isocyanide in more objects, as well as undertaking more detailed physico-chemical modeling of sources such as
IRAS16293.

Key words. astrochemistry — stars: formation — stars: protostars — ISM: molecules — ISM: individual objects: IRAS 16293–2422

3

in the ISM, with detections in a variety of low- and high-masssources (e.g. Bisschop et al. 2008; Beltrán et al. 2005; Zapata

arXiv:1807.04663v1 [astro-ph.SR] 12 Jul 2018

663v1 [astro-ph.SR] 12 Jul 2018o(Received January 1, 2018; Revised January 7, 2018; Accepted July 9, 2018)

A study of the c-C3 HD/c-C3 H2 ratio in low-mass star forming regions

Submitted to ApJ
J. Chantzos,1 S. Spezzano,1 P. Caselli,1 A. Chacón-Tanarro,1 L. Bizzocchi,1 O. Sipilä,1 and B. M. Giuliano1
1 Center for Astrochemical Studies,ABSTRACT
Max-Planck-Institut für extraterrestrische Physik

1
We use the deuteration of c-C3 H2 to probe Gießenbachstraße
the physical parametersof starless and protostellar cores, re+85748itGarchinglated to their evolutionary states, and compare
to the N(Germany)
2 H -deuteration in order to study possible di↵erences between the deuteration of C- and N-bearing species. We observed the main species c-C3 H2 , the singly
13 2018)(Received
January
1, 2018;
RevisedJanuary
7, the2018;
Accepted Julyand doubly deuterated
speciesc-C3 HDand c-C
well asisotopologue
c-H9,
CC2 H toward 10 star3 D2 , asless cores and 5 protostars in the Taurus and Perseus Complexes. We examined the correlation between the
Submitted to ApJ
N(c-C3 HD)/N(c-C3 H2 ) ratio and the dust temperature along with the H2 column density and the CO depletion
factor. The resulting N(c-C3 HD)/N(c-C3 H2 ) ratio is within the error bars consistent with 10% in all starless
ABSTRACT
cores with detected c-C3 HD. This also accounts forthe protostars except for the source HH211, where we meaWeuse
the deuteration
deuterationlevelof c-Cto probe
the physicalparametersof starless
protostellarhigher
cores, resurea highof 23%.
deuterationof N2 H+ follows
the sametrend butand
is considerably
3 H2 The+
dynamically
evolvedcore L1544.
We find itnotosignificant
betweenthe deuterationof c-C3 H2di↵erlatedintothetheirevolutionary
states,and compare
the N2 Hcorrelation-deuterationin orderto study possible
andthe CO thedepletion
factor among
the N-bearingstarless andspecies.
the protostellar
cores. Toward
thespecies
protostellar
thesingly
ences
betweendeuterationof C- andWe observed
the mainc-C3cores
H2 , theshow thelargestc-C
deuterium
fraction in c-C H2 . We
that the deuterationc-C2 Hcan trace
3 H2towardand coolest
doublyobjects
deuterated
speciesasshow
the isotopologuec-H13ofCC
10 star3 HD and c-C3 D2 , as3 well
+
the
early
phasesofstarformationandiscomparable
to
that
of
N
H
.
However,thelargestc-C
Hdeuteration2
3 2
less cores and 5 protostars in the Taurus and Perseus Complexes.
We examined the correlation
between thelevel is found toward protostellar cores, suggesting that while c-C3 H2 is mainly frozen onto dust grains in theN(c-C3 HD)/N(c-C3 H2 ) ratio and the dust temperature along with the H2 column density and the CO depletion
central regions of starless cores, active deuteration is taking place on ice.

factor. The resulting N(c-C3 HD)/N(c-C3 H2 ) ratio is within the error bars consistent with 10% in all starlesscores with detected c-C3 HD. This also accounts for the protostars except for the source HH211, where we meaKeywords: astrochemistry – line: identification – ISM: molecules – ISM: clouds
sure a high deuteration level of 23%. The deuteration of N2 H+ follows the same trend but is considerably higher
lo
iC
p core L1544.
5c We
p1.findn
5 betweenloin the dynamically
evolvedno significant
correlation
the deuteration of c-C3 H2
INTRODUCTION
p depletion factor dp and thelo
5 cores. Toward5t
5- 30 4 21
andd
the CO
amongcthe starless
protostellar
the protostellar
cores+the
During the early stages of star formation, self-gravitating starless cores begin to contract (nH > 104 cm 3 ) and to cool down
coolest objects
show the largest
deuterium fraction
in c-C
deuteration of 5
c-C3 H2+can Hn
trace
2 . We show that theLlopthese5cp3 Hofto a few Kelvin (T< 10 K). Underconditions, thedeuteration
molecules
is considerably increasing.
H2 D is the main+
the early
phasesstar
formationis comparable
to that fromof NL
H following. However,
the
c-C
2the
3 H2 deuteration
deuterium
providerforofmost
inand
dense
cores and is formed
reaction(Millar et al.
Le+ -molecules
30 4 21
cdeuteron-proton
plargest
lo
level
is
found
towardprotostellar
cores,
suggesting
that
while
c-C
H
is
mainlyfrozenonto
dust
grainsin the3 21989):
H
n
O
c
p
5
H
Nl
central regions of starless cores, active deuteration
is takingplace on ice.
+
+

O

O

H3 + HD ⌦ H2 D + H2 + 230 K.

(1)

This
reaction astrochemistry
is exothermic andproceeds
mostly in –theISM:
forwarddirection
at temperatures
Keywords:– line:identification
molecules– ISM:
clouds lower than 30 K, increasing the++abundance of H2 D . The abundance of H2 D also depends on the ortho-to-para-H2 ratio. The backward direction of reaction

Nitrogen fractionation in high-mass star-forming cores
across the Galaxy

5 Max-Planck-Institüt für extraterrestrische Physik, Giessenbachstrasse 1, D-85748, Garching bei München, Germany

Accepted 2018 April 13. Received 2018 April 13; in original form 2017 December 24

arXiv:1804.05717v1 [astro-ph.SR] 16 Apr 2018

rXiv:1804.05717v1 [astro-ph.SR] 16 Apr 2

I. Physikalisches Institut of the Universität zu Köln, D-50937 – Cologne, Germany
4 ESO, Karl Schwarzschild str. 2, D-85748 Garching, Germany

L. Colzi1,2⋆, F. Fontani2, V. M. Rivilla2, A. Sánchez-Monge3, L. Testi2,4,
M.
T. Beltrán2, and P. Caselli5
1

Università 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
ABSTRACT

3 I. Physikalisches Institut of the Universität zu Köln, D-50937 – Cologne, Germany
The fractionationof nitrogen(N) in star-forming regions is a poorly understood pro4 ESO, Karl Schwarzschildstr. 2, D-85748 Garching, Germany
5 Max-Planck-Institüt für extraterrestrische Physik, Giessenbachstrasse 1, D-85748, Garching bei München, Germany
cess. To put more stringent observational constraints on the N-fractionation, we haveobserved with the IRAM-30m telescope a large sample of 66 cores in massive starforming
regions.
We
the 13;(1–0)
rotationaltransitionof HN13 C, HC15 N, H13 CN
Accepted2018 April
13. targeted
Received 2018 April
in originalform 2017 December
24
and HC15 N, and derived the 14 N/15 N ratio for both HCN and HNC. We have completed this sample with thatABSTRACT
already observed by Colzi et al. (2018), and thus analysed
The fractionation(N) in star-forming regions is a poorly understood pro14
15 of nitrogena total sample of 87 sources.cess.
Theratiosobservational
are distributed
the Proto-Solar
To putN/
moreN
stringentconstraintsaroundon the N-fractionation,
we haveobserved
withtheIRAM-30m
telescopealarge
sampleof66
cores
in massive
starNebula value with a lower limit near the terrestrial atmosphere value (∼272).
We
have
13 C, HC15 N, H13 CN
forming
regions.
Wetargetedthe(1–0)
rotationaltransitionofHN
also derived the 14 N/15 N ratio
aN,function
ofthe
the
distance
and
14 Galactocentricand asHC15
and derived
N/15 N ratio for both HCN
and HNC.
Wededuced
have completed this samplestatistics.
with that alreadyby Colzi et al. (2018),
and thus analyseda linear trend based on unprecedented
Theobserved
Galactocentric
dependences
thata total sample of 87 sources. The 14 N/15 N ratios are distributed around the Proto-Solar
we have found are consistent,in the slope, with past works but we have found a new
Nebula value with a lower limit near the terrestrial atmosphere value (∼272). We have
14
15
local N/ N value of ∼400,alsoi.e.
closertheProsolar
Nebulavalue. A second
analysis
derivedthe 14toN/15
N ratio
as a functionof the Galactocentric
distance anddeducedalinear
trend
based
on
unprecedented
statistics.
The
Galactocentric
dependencesthatwas done, and a parabolic Galactocentric trend was found. Comparison with Galactic
we have found are consistent, in the slope, with past works but we have found a new
15 N value
chemical evolution models shows
theofslope
until
is consistentwiththe analysis
linearlocal 14 N/that∼400, i.e.
closer8tokpc
the Prosolar
Nebula value.
A second
was done,
andabovea parabolic
was found. Comparison
Galactic
analysis, while the flatteningtrend
8 Galactocentric
kpc is welltrend
reproducedby the withparabolicchemical evolution models shows that the slope until 8 kpc is consistent with the linear
analysis.
analysis, while the flattening trend above 8 kpc is well reproduced by the parabolic

C
6

5
k

1

analysis.

Key words:
– 5,/
ISM:
molecules– –ISM:
stars:– nucleosynthesis –HNstars: formation
pmassive
Key words:
stars: formation2C
molecules– stars: massive – nucleosynthesis –ISM: abundances
ISM: abundances

5

INTRODUCTION
H
m

c

M
R

C
m
IM

5

4

A
5
H
al. 2008). Manfroid et al. (2009) estimated a mean value
130 CHm4
of 14 N/15 N=148±6 from CN in 18 comets observed withm
A1 INTRODUCTION
5
Nitrogen, the fifth most abundant elementin the Universe
al. 2008).
Manfroid
et al. (2009)
estimateda weremean
value
VLT+UVES.
Diﬀerent valuesof 14 N/15 N
estimatedin
85 and the fourth most important14biogenic
element,in
14
15exists
the carbonaceous chondrite Isheyevo: ∼424 in a osbornite15

ofmain N/
N=148±6from CN in 18 comets observed withthe form of two stable isotopes: N (theone) andN.
bearing calcium-aluminium-rich inclusion (CAI) (Meibom etNitrogen, the fifth most abundant element
in15theUniverse
The 14 N/
N ratiois thought to be anVLT+UVES.
important indicatorDiﬀerent values of 14 N/15 N were estimated inal. 2007), and from 44 up to 264 (van Kooten et al. 2017) in85