Star Formation Newsletter#352 31-36
Yusuke Aso (KASI)Ø Orion
CSF=44%, MF=30% (VANDAM), 75 au
3000 auØØ ALMASOP, 43 Orion PGCCs, 140 au, Band 6, 7-m&12-m, 1.3 mm, CO 2-1, 3σ
Ø JCMT, 45 m, Spitzer, WISE
4. Results

0.002 Msun

4.1. Identiﬁcation of Binary/Multiple Systems

We focus on the 43 protostellar cores among 72 cores that
Ø 13
29
presellar
were detected in 1.3 mm continuum emission in ALMASOP(Dutta et al. 2020). The 1.3 mm continuum emission from theseØ ClumpFind, SCUBA-2 850 µmà
cores is relatively bright, and indicates that one or morecompact
objects, previouslyLJeans
identiﬁed
as young
protostars
Ø ALMA 1.3 mmà Menve+disk, Menve+disk / Mcore= 0.2-80%,
,M
= σNT
/ cs

Ø
LJeansØ 45-m N2H+ 1-0, 5
Ø MinimumSpanningTree

11(Dutta et al. 2020), have formed within them. Figure 1 presents
the infrared and (sub)millimeter continuum images obtainedwith various instruments for an exemplar core G196.92-10.37.
Multiple point sources are seen in the Spitzer image but some
may be contamination from background/foreground stars orvery evolved protostars because they do not show strong
1.3 mm continuum emission (Tobin et al. 2022). We will only
consider young protostars with disks and envelopes, whichshould have strong 1.3 mm continuum emission, in further
multiplicity analysis. From the highest-resolution ALMA
1.3 mm continuum image shown in the right panel, one canidentify a triple protostellar system formed in the exemplar coreG196.92-10.37. The image descriptions of the other cores arecompiled in Appendix.
We identify binary/multiple systems within the SCUBA-2
cores, whose sizes are smaller than or comparable to the FOVof the ALMA 12 m array, following the same strategy used inprevious works (e.g., Tobin et al. 2016, 2022). The core sizes
are listed in Tables 1 and 2. In total, we identify 13 binary/multiple systems and 29 single systems, and one binary-systemàà500 au 3500 au

KS

To quantify the multiplicity in each Orion GMC, we adopt
the statistical parameters of MF and CSF. They give a good
indication of the proportion of binary/multiple systems and theaverage number of companions. The two quantities associatedwith the number of star systems and companions are given by
MF =
CSF =

B + T + Q + ...
S + B + T + Q ...
B + 2T + 3Q + ...

(1 )
(2 )

© 2022. The Author(s). Published by the American Astronomical Society.

ALMA Survey of Orion Planck Galactic Cold Clumps (ALMASOP): How Do Dense
Core Properties Affect the Multiplicity of Protostars?
Qiu-yi Luo (罗秋怡)1,2 , Tie Liu (刘铁)1 , Ken’ichi Tatematsu3,4 , Sheng-Yuan Liu5 , Pak Shing Li6 ,James di Francesco7,8 , Doug Johnstone7,8 , Paul F. Goldsmith9 , Somnath Dutta5 , Naomi Hirano5 , Chin-Fei Lee5 ,Di Li10 , Kee-Tae Kim11,12 , Chang Won Lee11,12 , Jeong-Eun Lee13 , Xun-chuan Liu1, Mika Juvela14 ,Jinhua He15,16,17 , Sheng-Li Qin18 , Hong-Li Liu18 , David Eden19,20 , Woojin Kwon21,22 , Dipen Sahu5 ,Shanghuo Li11 , Feng-Wei Xu23,24 , Si-ju Zhang24, Shih-Ying Hsu5,25 , Leonardo Bronfman17 , Patricio Sanhueza4,26 ,Veli-Matti Pelkonen27 , Jian-wen Zhou2,10, Rong Liu2,10, Qi-lao Gu1, Yue-fang Wu23,24 , Xiao-feng Mai1 ,Edith Falgarone28 , and Zhi-Qiang Shen1
1

Ø

-

à
Ø λ Orionis:
Ø Orion A:Ø Orion B:
Ø ISF:
Ø L1641:àØØShanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030, Peopleʼs Republic of China; lqy@shao.ac.cn,
liutie@shao.ac.cn
School of Astronomy and Space Sciences, University of Chinese Academy of Sciences, No. 19A Yuquan Road, Beijing 100049, Peopleʼs Republic of China
3
Nobeyama Radio Observatory, National Astronomical Observatory of Japan, National Institutes of Natural Sciences, Nobeyama, Minamimaki, Minamisaku, Nagano384-1305, Japan
4
Department of Astronomical Science, The Graduate University for Advanced Studies, SOKENDAI, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
5
Academia Sinica Institute of Astronomy and Astrophysics, 11F AS/NTU Astronomy-Mathematics Building, No. 1, Section 4, Roosevelt Road, Taipei 10617,
Taiwan, R.O.C.
6
Astronomy Department, University of California, Berkeley, CA 94720-3411, USA
7
NRC Herzberg Astronomy and Astrophysics, 5071 West Saanich Road, Victoria, BC, V9E 2E7, Canada
8
Department of Physics and Astronomy, University of Victoria, 3800 Finnerty Road, Elliot Building, Victoria, BC, V8P 5C2, Canada+
9
Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
10
National Astronomical Observatories of China, Chinese Academy of Sciences, Beijing 100012, Peopleʼs Republic of China
11
Korea Astronomy and Space Science Institute, 776 Daedeokdae-ro, Yuseong-gu, Daejeon 34055, Republic of Korea
12
University of Science and Technology, Korea (UST), 217 Gajeong-ro, Yuseong-gu, Daejeon 34113, Republic of Korea
13
The School of Space Research, Kyung Hee University, 1732 Deogyeong-daero, Giheung-gu, Yongin-si, Gyeonggi-do, Republic of Korea
14
Department of Physics, P.O. Box 64, FI-00014, University of Helsinki, Finland
15
Yunnan Observatories, Chinese Academy of Sciences, 396 Yangfangwang, Guandu District, Kunming 650216, Peopleʼs Republic of China
16
Chinese Academy of Sciences South America Center for Astronomy, National Astronomical Observatories, CAS, Beijing 100101, Peopleʼs Republic of China
17
Departamento de Astronomía, Universidad de Chile, Las Condes, 7591245 Santiago, Chile
18
Department of Astronomy, Yunnan University, Kunming 650091, Peopleʼs Republic of China
19
Astrophysics Research Institute, Liverpool John Moores University, IC2, Liverpool Science Park, 146 Brownlow Hill, Liverpool, L3 5RF, UK
20
Armagh Observatory and Planetarium, College Hill, Armagh, BT61 9DB, UK
21
Department of Earth Science Education, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Republic of Korea
22
SNU Astronomy Research Center, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Republic of Korea
23
Department of Astronomy, School of Physics, Peking University, Beijing 100871, Peopleʼs Republic of China
24
Kavli Institute for Astronomy and Astrophysics, Peking University, Haidian District, Beijing 100871, Peopleʼs Republic of China
25
National Taiwan University (NTU), No. 1, Section 4, Roosevelt Road, Taipei 10617, Taiwan (R.O.C.)
26
National Astronomical Observatory of Japan, National Institutes of Natural Sciences, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
27
Institut de Ciències del Cosmos, Universitat de Barcelona, IEEC-UB, Martí i Franquès 1, E-08028 Barcelona, Spain
28
LPENS, Ecole Normale Supérieure, Université PSL, CNRS, Sorbonne Université, Université de Paris, 75005 Paris, France
Received 2022 March 7; revised 2022 April 12; accepted 2022 April 12; published 2022 June 6
2

N2H

HII

UV

A

A

B

MF, CSFà

CSF

CO
During the transition phase from a prestellar to a protostellar cloud core, one or several protostars can form within asingle gas core. The detailed physical processes of this transition, however, remain unclear. We present 1.3 mm dustßcontinuum and molecular line observations with the Atacama Large Millimeter/submillimeter Array toward 43
Abstract

protostellar cores in the Orion molecular cloud complex (λ Orionis, Orion B, and Orion A) with an angular resolutionof ∼0 35 (∼140 au). In total, we detect 13 binary/multiple systems. We derive an overall multiplicity frequency(MF) of 28% ± 4% and a companion star fraction (CSF) of 51% ± 6%, over a separation range of 300–8900 au. The

MF, CSFØØ
Ø HMCØ W49Nty of Japan, (2022), Vol. 00, No. 0

8 using 43–45 12-m antennas
9–12 7-m antennas of Morita
elines for the 12-m antennas
tively. Those for the 7-m anspectively. The two datasets
7-m antennas were concatee data was not used. Flux,
brations were carried out with
22+1530, J1830+0619.

.90–218.90 GHz, 218.85–, and 232.73–234.73 GHz),h, were set up to observe theis was done using the CASA
We separated the continuumar baseline to line free chang ‘uvcontsub’ task of CASA.
e frequency of 226 GHz was
ree intensities of all the four

up a data cube with a specugh the frequency resolution⇠1.4 km s 1 ), there was variaon between datasets obtainedd the flux received in an origrest 2 kms 1 bin in order toS) = 19h 10m 13s. 5, (ICRS)
ameters of ‘tclean’ task as
0.5’. This setting creates anatural and uniform weighttio of the measurements andhe noise threshold. The syn-

HMC
HMC

arXiv:2204.04617v2 [astro-ph.GA] 20 May 2022

W49N MCN-a: a disk-accreting massive protostar
embedded in an early-phase hot molecular core
Ryosuke Miyawaki1 , Masahiko Hayashi2,3 , and Tetsuo Hasegawa2
1

College of Arts and Sciences, J.F. Oberlin University, Machida, Tokyo 194-0294, Japan
National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
3
JSPS Bonn Office, Ahrstr. 58, 53175 Bonn, Germany
2⇤

E-mail: miyawaki@obirin.ac.jp

UCHII
Abstract

ALMA
3>100 K, >107 cm-3, COMs, 104-105 yr

Received h27–September–2021i; Accepted h10–April–2022i

HCHII, UCHII

We present ALMA archival data for 219–235 GHz continuum and line observations toward the hotmolecular core (HMC) W49N MCN-a (UCHII region J1 ) at a resolution of ⇠0.00 3. The dust continuum
emission, showing an elongated structure of 100. 40 ⇥ 000. 95 (PA=43.5 ) perpendicular to the outflow
seen in SiO and SO, represents a rotating flattened envelope, or torus, with a radius of 7,800 au
inclined at 47.5 or larger. The emissions from CH3 CN, 13 CS, HNCO, HC3 N, SO2 , DCN, H2 CO,OCS, CH3 OH, and C18 O exhibit a consistent velocity gradient as a result of rotation. The magnitudeof each velocity gradient is different, reflecting that each line samples a specific radial region. This
allows us to derive a rotation curve as Vrot / R0.44±0.11 for 2,400 au . R . 14,000 au, giving the dy1.88
namical mass as Mdyn = 57.0+24.5
M . The envelope mass independently estimated17.1 (R[au]/3,000)
from the dust emission is 910 M (for T dust = 180 K) for R  7,800 au and 32 M (for T dust = 300 K) forR  1,700 au. The dynamical mass formula agrees well with these mass estimates within an uncertainty of a factor of three in the latter. The envelope is self-gravitating and is unstable to form spiralarms and fragments, allowing rapid accretion to the inner radii with a rate of order 10 2 M yr 1 , although inward motion was not detected. The envelope may become a non self-gravitating Kepleriandisk at R . (300–1,000) au. The formula is also consistent with the total mass ⇠104 M of the entire
HMC 0.15 pc (31,000 au) in radius. Multiple transitions of CH3 CN, HNCO and CH3 OH provide the+52+73
rotation temperatures of 278 +39
30 K, 297 39 K, 154 37 K, respectively, for R . 1,700 au, suggestingthat the central source of MCN-a has an intrinsic bolometric luminosity of ⇠ 106 L . These results
have revealed the structure and kinematics of MCN-a at its intermediate radii. With no broad-line
H30↵ emission detected, MCN-a may be in the earliest phase of massive star formation.

12-m&7-m, Band6, dv=2 km/s, 0.3", 11 kpc, σ=4.3 mJy/beam for lines

Key words: ISM: clouds, ISM: molecules – radio lines: ISM: individual (W49A Molecular Cloud), stars: massive, formation

1 Introduction

sive stars is only partially o↵set by their large luminosities,

arXiv:2204.04617v2 [astro-ph.GA] 20 May 2022

W49N MCN-a: a disk-accreting massive protostar
embedded in an early-phase hot molecular core
Ryosuke Miyawaki1 , Masahiko Hayashi2,3 , and Tetsuo Hasegawa2

Publications of the Astronomical Society of Japan, (2022), Vol. 00, No. 0

30

C18O

HNCO

CS

13

SiO

20
10
0
-10
30 SO

SO2

OCS

HC3N

DCN

CH3OH

CH3CN

20
10
0
-10
30 H2CO
20
10
0
-10

NE -1

0

1

-1

0

1

-1

0

Offset (arcsec)

1

-1

0

1 SW

1

College of Arts and Sciences, J.F. Oberlin University, Machida, Tokyo 194-0294, Japan
National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
3
JSPS Bonn Office, Ahrstr. 58, 53175 Bonn, Germany
2⇤

E-mail: miyawaki@obirin.ac.jp

Received h27–September–2021i; Accepted h10–April–2022i

Abstract
We present ALMA archival data for 219–235 GHz continuum and line observations toward the hotmolecular core (HMC) W49N MCN-a (UCHII region J1 ) at a resolution of ⇠0.00 3. The dust continuum
emission, showing an elongated structure of 100. 40 ⇥ 000. 95 (PA=43.5 ) perpendicular to the outflow
seen in SiO and SO, represents a rotating flattened envelope, or torus, with a radius of 7,800 au
inclined at 47.5 or larger. The emissions from CH3 CN, 13 CS, HNCO, HC3 N, SO2 , DCN, H2 CO,OCS, CH3 OH, and C18 O exhibit a consistent velocity gradient as a result of rotation. The magnitudeof each velocity gradient is different, reflecting that each line samples a specific radial region. This
allows us to derive a rotation curve as Vrot / R0.44±0.11 for 2,400 au . R . 14,000 au, giving the dy1.88
namical mass as Mdyn = 57.0+24.5
M . The envelope mass independently estimated17.1 (R[au]/3,000)
from the dust emission is 910 M (for T dust = 180 K) for R  7,800 au and 32 M (for T dust = 300 K) forR  1,700 au. The dynamical mass formula agrees well with these mass estimates within an uncertainty of a factor of three in the latter. The envelope is self-gravitating and is unstable to form spiralarms and fragments, allowing rapid accretion to the inner radii with a rate of order 10 2 M yr 1 , although inward motion was not detected. The envelope may become a non self-gravitating Kepleriandisk at R . (300–1,000) au. The formula is also consistent with the total mass ⇠104 M of the entire
HMC 0.15 pc (31,000 au) in radius. Multiple transitions of CH3 CN, HNCO and CH3 OH provide the+52+73
rotation temperatures of 278 +39
30 K, 297 39 K, 154 37 K, respectively, for R . 1,700 au, suggestingthat the central source of MCN-a has an intrinsic bolometric luminosity of ⇠ 106 L . These results
have revealed the structure and kinematics of MCN-a at its intermediate radii. With no broad-line
H30↵ emission detected, MCN-a may be in the earliest phase of massive star formation.
Key words: ISM: clouds, ISM: molecules – radio lines: ISM: individual (W49A Molecular Cloud), stars: massive, formation

1 Introduction

sive stars is only partially o↵set by their large luminosities,

Downloaded from https://academic.oup.com/mnras/article/512/4/6038/6553845 by KASI user on 08 July 2022

Downloaded from https://academic.oup.com/mnras/article/512/4/6038/6553845 by KASI

usedboundary condition. These simplifications do not affectfurther keep the gas and dust surface densities at thMorbidelli & Masset (2006) parameter
cted
conclusions but are numerically convenient. Coupled with
ALMA constraints on assembly of core accretion planets
fixed, while allowing the dust and gas to freely
veral
by equation (1), this density profile results in a radially co! "2inner boundary (such boundary conditions are
3HH
M∗
accretion rate in the disc, Ṁ . To keep our disc in thi
theSergei Nayakshin ,1 ‹ Vardan
Elbakyan1,2 ‹ and Giovanni Rosotti 1
Cp =+ 50αv(4)‘evanescent’; Zhang et al. 2018).
1 School of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK
further keep the gas and dust surface densities at the outer
4RH
a
Mp
udes
2 Research Institute of Physics, Southern Federal University, Rostov-on-Don 344090, Russia
fixed, while allowing the dust and gas to freely pass th
disc
to differentiate between type I planet migration (no deep gap in the
inner boundary
boundary conditions are sometim
2.2 Planet(suchaccretiongas Ø
Accepted 2022 March 22. Received 2022 March 22;ALMAin original form 2021 December 17
~10
Myr
ALMA
constraints
oncore
accretion
6039‘evanescent’; Zhang et al. 2018).
gas surface density at the location of the planet), Cp ≥ 1, and type IIdisc,˙ − on to our plane
To model gas accretion term !
regime(a deep gap is opened), Cp ≤ 1. In the type I regime we use
ØCAion. CORALIE/HARPS sample (Bennett, Ranc & Fernandes
Bern model for planet formation (e.g.
ABSTRA
C T ) indi2021
the tidal torque over the whole disc gives the total rate wellof theknown
angular
Paardekooper,
Baruteau& Kley (2011) expressions
for &t , whereas
Ø
ALMA
CA
2.2
Planetaccretion
Resolved
dust
continuum
and
CO
line
ALMA
imaging,
and
in
some
cases
detectionofH
αemission,
hint
that
young
ysis cated instead a single power-law mass function from ∼ 10 M⊕ into
2021a,b&).t In
the Bern model, the gas capture radiu
momentum
gain of the disc due to planet–disc interaction,(cf.massive
in type II regime the tidal torque is an planets
integral(cf.
equationA1)
are abundant at wide separations in protoplanetary discs. Here we show how these observationsdefined
can probeasthe runaway
ngs. the Jovian regime. Furthermore, modern 3D numericalsimulations
equation
A1). We note in passing that &t canbeTopositive(theplanet˙ − on to our planets we
model
accretionof planetaryin the Coreright rangeof massesgas
to accountfor theterm !
over the specific torque λ! t , given by the phasewidelyused growth
expression
inAccretion theory. Planets in this phase have the
rates
on
to
planets(Szulágyi
migrates
inward)
or
ne
gativ
e
(the
planetmigratesoutwards).
The
duce find much smaller gas accretion
kacc
RH R
predominantly moderate contrast gaps and rings seen in ALMA observations. However, we findthat known
these planets
gain
mass
and
acc
)
well
model
for planet
formation (e.g. Emsenh
)(.*,
the
literature(Lin&
Papaloizou
1986; Armitage&very
Bonnell2002; the phase
Rgc to=Bern," , 𝐻 2015
Ø
1D
𝑇
∝
𝑅
∝
𝑅
,
⾒
migrateinwardrapidly.
Asaresult,
when
they
could
producegaps
withproperties
similarthoseobserved
is
et
al.
2014
;
Ormel,
Shi&
Kuiper;Fung&
Chiang2016;
conservationoftheangularmomentuminthedisc–planet
systemown
Racc+ kmodel,2021a,btens). IntotheBern
acc RH the gas capture radius of thvery
short,
i.e.
tgap !
0.1 Myr,
independentlyof thediscviscosity parameter.
This would
require as
manyhundreds of gas)(
Lodato
&
Clark
e
2004
;
Alexander,
Clark
e
&
Pringle2006;
LodatoLambrechts
&
Lega
2017
;
Lambrechts
et
al.
2019
)
than
previous
demandsthattheplanet–star
separationaevolves
200 auΣ ∝realistic
𝑅 discs.
n be Ø
as Thisgiant planets to be born per ALMA system, violating the available mass budget of solids indefined
also=predicts
where
Racc
GMp /cs2 and kacc = 1/4. Gas accretio
et al. 2009
; Dipierro & Laibe 2017):
1D
studies
found.
preponderance
of
discs
with
very
wide
gaps
or
completeinner
discholes,
whichisnotobserved.
We
show
that
suppression
of
!
"
as to
kacc
RH Racc
3D
regimeforlow
da by a factor
2&tof at leasta ten is1/a2possible solutionaUsing the census of planets growing in their discs
compiled
both planetaccretionby
and migration
to these serious
problems.
Futurepopulation
Rgc =, mass planets, when Rgc ≤ H, and
=
−
=
−
,
(3)
sion
&
2 %
4 GM∗Dipierro & Szulágyi
Rplanetarykacc
RH andwhen Rgc > H. The maximum
massplanetsacc +synthesis
modelsof planet formation
toGM
address
both exoplanetarysystems
Lodato et al. (q2019), aNayakshin,(2019) showed
dt should
Maimtmig data of older disc-lesshighp∗
λt = ffor R > aALMA discs with embedded planets in one framework.
accretion rate on to the planet in Emsenhuber et al.
that ALMA planets
must bea growing ∼ an order of magnitude
2 (Rwhere Racc = GMp /cs2 and kacc = 1/4. Gas accretion proc
where
we defined
the interactions
planet migration
time,discs.
tmig . We use the Crida,!
"4
Key words: planets and satellites:
formation– planet–disc– protoplanetaryslower than CA 2scenario
3D regime
Ṁ2Dfor= low
2Rgcmass!(a)planets,
vrel , when Rgc ≤ H, and in 2Dq
R predicts.
GM∗ Nayakshin et al. (2019) used
Morbidelli& Masset (2006) parameter
idealized
gas-only models for ALMAλt =power-law−ffor R discs< a,and neglected(5)Bernhigh mass planets when Rgc > H. The maximum (runawa
2 In (Rwherev rel planets= max[
planet migration.
this paper,a we extend this work in several
candidate(e.g."K Rgc , cs ].
! " exoplanets orbiting disc-less stars, ALMA

their models until disc dispersal (e.g. Pollack et al. 1996; Ida &range, that is, from ∼ twice Neptune (0.1 MJ ) to ∼ Jupiter (1 MJ )Downloaded from https://academic.oup

accretion rate on to the planet in Emsenhuber et al. (2021a
1 I N T RO D U C T I O NBern3HΣ ; Andrews
H 2ALMAM∗ Partnership 2015
et al. 2018
LongBern
et al. 2018;
In ;themodel,
the gap opening in the dissignificant ways. We include planet migration, and calculate the
C
=
+
50
α
(4)
p
v
A
planetformation
theoryisasetofequationsdescribing
evolution
Pinte
et
al.
2020
)
must
be
evolving
right
now,
rather
than
in
their
where
(
R
=
|
R
−
a
|
and
the
factorf
isaconstant
set
to
f
=
0.5
4
R
a
M
Ṁ
=
2
R
!(
a)
v
,
H
p
2Ddirectgc
rel from first principles since the planet
notcomputed
time-dependent structure of discs via a 1D modelthat
includesof planet
variables,such as its mass Mp , separationa, metallicity
long forgotten
past, promising more
observational
constraints
here.
The
torqueterm
divergesattheplanetlocation,
and
hence
one
z
,
etc.,
insidetheparentprotoplanetary
disc.
Protoplanetary
disc
on
the
functionsF.
Ø
HD163296,
M
=2.04
Msun,
L
=17
Lsun,
t
=5
Myr,
T=65
K@100
au,
86
au
ΔR/a=0.17ithe disc *applied to the disc while the planet is in the type I* torque exchange between*pg of a self-consistent gravitationalwherev thismax["focusingrel =K Rgc , cs ].
evolution is itself a field of intense
research (Williamsbetween& Cieza typeIn Ithis
paper, weillustrate thepowerdeepofapproachtodifferentiate
planetmigration
(no
gap
in by
the
smooths
it
for
|
(
R
|
<
max
[
H
,
R
]
(e.g.
Syer
&
Clarke1995).
As
and theMplanet,
includingdisc
gap opening.
We2011also
includegas
H
The moti
vationfor this approach is the fact that the;Alexander
et
al.
2014
),
with
data
indicatingatremendous
on
a
key
step
in
the
Core
Accretion(CA)
scenarioforplanetformation
=0.2
M
,
5-200
au
Inp ≥
the1,Bernmodel,
the gap opening in the disc by th
disc
sun
a&
gas
surfacedensityatthelocationoftheplanet),
C
and
type
II
varietyin protoplanetaryproperties even for stars of similar(e.g. Safronov 1972; Pollack et al. 1996). In
all current
vours of CA,
a numberof authors
in the past
we usemassa prescription
todisctransition
accretion
on to planets
by explicitly
removingfromthe disc,gas
disc fla
weaklyexcept very close to it, so !(a) i-3
not computed
from
first
since the planet tidal toregime(aal.
deep
is opened),
In theItheregimeweuse014; thusØcombining
mass, age, andenvironment(e.g.
Manara et
2017;gap
Andrews
when a C
planetary(solid)core typereaches
critical massof∼
10 Mprinciples
amax=1.5
mm,
M
~1
M
,
α=10
0.5
Myr
(
)
p ≤ 1.
⊕
pJ
constraints
fromaccretionand migration.
approximatelytheunperturbed
gas surface densitysmoothly fromtype I to
typeplanet
II planet
migration(see appendix
Afor2020). Furthermore,
exoplanetary dataareverystrongly
dominated
while
still
embeddedinthegaseous
protoplanetary
disc,
a
very
rapid
applieddisc while the planet is in the type I migrati
Paardekooper, Baruteau & Kley (2011) expressions
forto&thet , whereas
For Finally, dust dynamics in the disc is solved for, byenabling
analysisplanets orbitingstars much older than ∼10 Myr (e.g. Winn &– and thus called runaway – gas accretionthen
on to theplanet setsthatin (e.g.
assumesa deep gap
in theondetail).
Themotivationfor
approachis thefactdisc
thatemerges
the planet
intype
IIofregime
the tidalMizuno
torqueisan integral(cf.
equationA1this) 2000
y
2015
).
These
stars
have
lost
all
signs
their
primordial
1980;
Stevenson
1982
;
Ik
oma,
Nakazaw
a
&
Emori
).
ork, of time evolution of planet-induced dust gaps, innerFabryck
holes, andrings.
We except
note
that
is atocommon
The protoplanetary disc viscosity is discs
given
by theythegrew.
Shakurafrom which
This makesit&
impossible
to ascertain
the λtThe
runawayterminates
when gas
theusedplanetreaches∼ Jovianmass anddiscunity.
weaklyverythisclose
it, so !(approximata) in equat
o
v
er
the
specific
torque
,
given
by
the
widelyexpression
inthin Our paper is organized as following. In Section
2 weofintroduce
synthesisforplanetproperties
the disc in which
opens a deep gap in the surrounding gaseousdisc (Bate,
Bonnell& formation (e.g. Coleman & Ne
1/2a given planet formed. We also face
Sunyaev (1973) model, ν = αcs H, where
c
=
(
P
/
ρ)
is
the
approximatelytheunperturbed gas surface density. The B
literature(Lin& Papaloizou
1986& Bonnell
2002sfor the planetsthe
in theSolar System.
Therefore,
Bromm 2003). For;a Armitage
population of growing
planets, very
few;planets
our methods, in Section 3 we apply these methodssimilar
to auncertainties
well
known
Due
to
the
aims
ofinour
however,
gapC forinbeing
the last several
decades,
to compare
planetformationmodel ; Alexander,
are in the runaway
phase
at anygivenassumes
time;most; areeithertoo lowthenthat
a deepgap
thepaper,disc emerges
once
Lodato& Clark
e 2004Clarke&Pringle2006
Lodatoisothermal
soundspeed,
with
P
and
ρ
the
disc
mid-planepd
planets
can be theorists had to make do with statistical
disc
must
be
explicitly
resolved
since
dust
is
usual
iscs protoplanetary disc in HD163296 to illustrate how
predictions
to observations
mass or already too massive to be accretinggas rapidly. Accordingly,
unity. Wenote that
this is a common approximation in
et al. 2009; Dipierro & Laibe2017):
pressure and density.
assumptions
the disc
CA theories predict a pronounced planet planets
desert in thestronger
runaway masstheseabout
ideas
to structure and parameters, and then run
than gas(Dipierro
et al.
2016), sosuch used to constrain CA scenario. In Section 4 we apply
synthesis for planet formation(e.g.
Coleman& Nelson20Advance Access publication 2022 March 24

ALMA constraints on assembly of core accretion planets
Sergei Nayakshin ,1 ‹ Vardan Elbakyan1,2 ‹ and Giovanni Rosotti

1

1 School of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK
2 Research Institute of Physics, Southern Federal University, Rostov-on-Don 344090, Russia

Accepted 2022 March 22. Received 2022 March 22; in original form 2021 December 17

ABSTRACT

Resolved dust continuum and CO line ALMA imaging, and in some cases detection of H α emission, hint that young massive
planets are abundant at wide separations in protoplanetary discs. Here we show how these observations can probe the runaway
phase of planetary growth in the Core Accretion theory. Planets in this phase have the right range of masses to account for the
predominantly moderate contrast gaps and rings seen in ALMA observations. However, we find that these planets gain mass andmigrate inward very rapidly. As a result, the phase when they could produce gaps with properties similar to those observed isvery short, i.e. tgap ! 0.1 Myr, independently of the disc viscosity parameter. This would require many tens to hundreds of gas
giant planets to be born per ALMA system, violating the available mass budget of solids in realistic discs. This also predicts
preponderance of discs with very wide gaps or complete inner disc holes, which is not observed. We show that suppression ofboth planet accretion and migration by a factor of at least ten is a possible solution to these serious problems. Future population
synthesis models of planet formation should aim to address both exoplanetary data of older disc-less planetary systems and
ALMA discs with embedded planets in one framework.
Key words: planets and satellites: formation – planet–disc interactions – protoplanetary discs.

1 I N T RO D U C T I O N
A planet formation theory is a set of equations describing evolutionof planet variables, such as its mass Mp , separation a, metallicity
zp , etc., inside the parent protoplanetary disc. Protoplanetary discevolution is itself a field of intense research (Williams & Cieza
2011; Alexander et al. 2014), with data indicating a tremendous
variety in protoplanetary disc properties even for stars of similarmass, age, and environment (e.g. Manara et al. 2017; Andrews
2020). Furthermore, exoplanetary data are very strongly dominatedby planets orbiting stars much older than ∼10 Myr (e.g. Winn &Fabrycky 2015). These stars have lost all signs of their primordial
discs from which they grew. This makes it impossible to ascertain theproperties of the disc in which a given planet formed. We also facesimilar uncertainties for the planets in the Solar System. Therefore,
in the last several decades, to compare planet formation model
predictions to observations theorists had to make do with statisticalassumptions about the disc structure and parameters, and then run

exoplanets orbiting disc-less stars, ALMA candidate planets (e.g.
ALMA Partnership 2015; Andrews et al. 2018; Long et al. 2018;
Pinte et al. 2020) must be evolving right now, rather than in theirlong forgotten past, promising more direct observational constraints

A model grid for the reflected light from transition disks
A1 model grid1, for the reflected light from transition disksJ. Ma and H.M. Schmid

J. Ma1 and H.M. Schmid1,

Institute for Particle Physics and Astrophysics, ETH Zurich, Wolfgang Pauli Strasse 17, CH-8093 Zuriche-mail: jma@phys.ethz.ch
Institute for Particle Physics and Astrophysics, ETH Zurich, Wolfgang Pauli Strasse 17, CH-8093 Zuriche-mail: jma@phys.ethz.ch

Received –; accepted –Received –; accepted –ABSTRACT
Context. The dust in protoplanetary disks is an important ingredient in planet formation and can be investigated with model simula-tions and quantitative imaging polarimetry of theContext.
scatteredThestellardustlight.
in protoplanetary disks is an important ingredient in planet formation and can be investigated with model simulaAims. This study explores circumstellar disks with calculations for the intensity and polarization of the reflected light. We aim
tions and quantitative imaging polarimetry of the scattered stellar light.
to describe the observable radiation dependencies on parameters in order to constrain the dust scattering properties and the disk
Aims. This study explores circumstellar disks with calculations for the intensity and polarization of the reflected light. We aim
geometry.
to describe the observable radiation dependencies on parameters in order to constrain the dust scattering properties and the disk
Methods. The photon scattering and absorption by the disk are calculated with a Monte Carlo method for a grid of simple, rotationallygeometry.
symmetric models approximated at each point by a plane-parallel dusty atmosphere. The adopted geometry is described by a strongly
Methods. The photon scattering and absorption by the disk are calculated with a Monte Carlo method for a grid of simple, rotationally
illuminated inner wall of a transition disk with inclination i, a constant wall slope , and an angular wall height ↵. Dust scattering
symmetric models approximated at each point by a plane-parallel dusty atmosphere. The adopted geometry is described by a strongly
parameters are the single scattering albedo !, the Henyey-Greenstein scattering phase function with the asymmetry parameter g,illuminated inner wall of a transition disk with inclination i, a constant wall slope , and an angular wall height ↵. Dust scatteringand the maximal fractional polarization pmax induced by the scattering. First, the results for the reflectivity, the polarized reflectivity,
parameters are the single scattering albedo !, the Henyey-Greenstein scattering phase function with the asymmetry parameter g,
and the fractional polarization of a plane-parallel surface element are calculated as functions of the incidence angle and the escapeand the maximal fractional polarization p induced by the scattering. First, the results for the reflectivity, the polarized reflectivity,
direction of the photons and as functions of the scattering parameters. Integration over allmax
escape directions yields the surface albedo
and the fractional polarization of a plane-parallel surface element are calculated as functions of the incidence angle and the escapeand the fraction of radiation absorbed by the dust. Second, disk images of the reflected intensity and polarization are calculated, and the
direction ofcombinations.
the photons andfunctionsof thescatteringparameters.
Integration
over all escape directions yields the surface albedo
appearance of the disk is described for various parameter
Theasimages
providemany
quantitative
radiation
parameters
and the fraction of radiation absorbed by the dust. Second, disk images of the reflected intensity and polarization are calculated, and thefor a large range of model calculations, which appearance
can be comparedto observations.
includethe diskcombinations.
integrated intensity
I/I? , provide many quantitative radiation parametersof the disk
is described Thesefor various
parameter
The images
azimuthal polarization Q' /I? , the polarization aligned
withtheapparent
disk
axes
Q/I
? , the quadrant polarization parameters Q xxx
for a large range of model calculations, which can be compared to observations. These include the disk integrated intensity I/I? ,and U xxx , the disk-averaged fractional polarization hp' i or hpQ i, but also the front-to-back intensity ratio I180 /I000 or the maximum
azimuthal polarization Q' /I? , the polarization aligned with the apparent disk axes Q/I? , the quadrant polarization parameters Q xxx
fractional scattering polarization max(p' ).
and U xxx , well
the disk-averaged
fractional
hp' i or hpQ i, but also the front-to-back intensity ratio I180 /I000 or the maximum
Results. The results of our simple disk models reproduce
the measurements
for I/Ipolarization? , Q' /I? , and hp' i reported for well-observed
scatteringpolarization' ).
transition disks. They describe the dependenciesfractionalof the scatteredradiationon the max(pdisk geometry
and the dust scattering parameters in
Results.canTheberesultsof oursimpledisk
models reproduce
measurements
for I/I? , Q' /I? , and hp' i reported for well-observed
detail. Particularly strong constraints on disk properties
obtainedfromcertaindiagnostic
quantities:wellfor theexamplethe fractionaltransition
disks.
They describe
the dependencies
scatteredradiation on inclinathe disk geometry and the dust scattering parameters inpolarization hp' i or max(p' ) depend predominantly
on thedust-scatteringparameters! and g; offorthedisks
with well-defined
detail.
Particularly
on disk properties
can wallbe obtained
certain diagnostic quantities: for example the fractionaltion, ratios of the quadrant polarization parameter
dependmainly strongon theconstraints
scattering asymmetryg and theslope ;fromwavelengthpolarization
hp' iwavelength
or max(p' )dependence
depend predominantly
on the dust-scattering
dependencies of I/I? and Q' /I? can mostly be attributed
to theof the dust scatteringparameters !(parameters), g( ), ! and g; for disks with well-defined inclinaratios oflightthe ofquadrant
parameter
mainly onR theand pmax ( ); and the ratio between the scatteredtion,and thermal
the diskpolarization
roughly constrains
thedependdisk reflectivity
andscattering
the singleasymmetry g and the wall slope ; wavelength
dependencies of I/I? and Q' /I? can mostly be attributed to the wavelength dependence of the dust scattering parameters !( ), g( ),scattering albedo of the dust !.
pmax( ); andradiation
the ratio between
the scatteredand thermal
light ofdependencies
the disk roughly
Conclusions. This computational investigation andof thescatteredfrom transition
disks shows
well-definedon constrains the disk reflectivity R and the single
scatteringof thetool
dustfor!.the analysis of quantitative measurements, specificallymodel parameters and the results can therefore beused as aalbedo
diagnostic
Conclusions.
computationalof thescatteredradiationfrom transition disks shows well-defined dependencies onin constraining or even determining the scattering
properties ofThis
the dust
particles ininvestigation
disks. Collecting
andcomparingsuch information
model ofparameters
and thecan thereforedisks.
be used as a diagnostic tool for the analysis of quantitative measurements, specificallyfor many systems is required to understand the nature
the scattering
dustresultsin planet-formingin constraining or even determining the scattering properties of the dust particles in disks. Collecting and comparing such information
Key words. circumstellar disks – dust scatteringradiative
transfer– polarization– transition
disks of the scattering dust in planet-forming disks.
for–manysystems
is required
to understandthe nature

1. Introduction

rXiv:2204.06370v1 [astro-ph.EP] 13 Apr 2022

arXiv:2204.06370v1 [astro-ph.EP] 13 Apr 2022

ABSTRACT

Key words. circumstellar disks – dust scattering – radiative transfer – polarization – transition disks

the complementary information from all these observations (e.g.,Andrews 2015).
1. Introduction
the complementary information from all these observations (e.g.,
Dust is an important ingredient of the planet formation in proThis work simulates with model calculations
the2015).
photometAndrews
toplanetary disks. Dust particles can be observed over a large ric and polarimetric properties of the stellar light scattered by the
Dust is anorimportant
planet formationin simulations
proThisworkwith model calculations the photometwavelength range as strong absorbers, scatterers,
emitters ingredient
inner wallofofthetransitions
disks. The
shouldbe simulates
usefultoplanetarydisks.
Dust
particles
canbeobserved
over
a
large
ric
and
polarimetricpropertiesof the stellar light scattered by theof radiation and the data show a large diversity of geometric for comparisons with high-resolution and high-contrast obser-

Qxxx & Uxxx

Departamento de Física Aplicada, Facultad de Ciencias, Universidad de Alicante, Carretera de San Vicente s/n, E03690, San
Vicente del Raspeig, Spain e-mail: ignacio.negueruela@ua.es
2
Instituto de Astrofísica de Andalucía, CSIC, Glorieta de la Westerlund
Astronomía s/n, E18008,
Granada, Spain
1 underthe light of Gaia EDR3:
3
Instituto de Astrofísica de Canarias, Vía Láctea s/n, E38200, La Laguna, Tenerife, Spain
4
Distance,
extent,and a hidden population? .
Universidad de La Laguna, Departamento de Astrofísica,
E38206 Laisolation,
Laguna, Tenerife,
Spain
5
Departamento de Física, Ingeniería de Sistemas y Teoría de la Señal, Universidad de Alicante, Carretera de San Vicente s/n,
I. Negueruela1 , E. J. Alfaro2 , R. Dorda3, 4 , A. Marco5 , J. Maíz Apellániz6 , and C. González-Fernández7
E03690, San Vicente del Raspeig, Spain
6
Centro de Astrobiología, CSIC-INTA. Campus ESAC. C. bajo del castillo s/n. E-28 692 Villanueva de la Cañada, Madrid, Spain
7
1
Institute of Astronomy, University of Cambridge,
MadingleyRoad,
Cambridge
CB3
UKUniversidad de Alicante, Carretera de San Vicente s/n, E03690, San
Departamentode Física
Aplicada,
Facultadde 0HA,
Ciencias,

Vicente del Raspeig, Spain e-mail: ignacio.negueruela@ua.es
Instituto de Astrofísica de Andalucía, CSIC, Glorieta de la Astronomía s/n, E18008, Granada, Spain
3
Instituto de Astrofísica de Canarias, Vía Láctea s/n, E38200, La Laguna, Tenerife, Spain
4
Universidad de ABSTRACT
La Laguna, Departamento de Astrofísica, E38206 La Laguna, Tenerife, Spain
5
Departamento de Física, Ingeniería de Sistemas y Teoría de la Señal, Universidad de Alicante, Carretera de San Vicente s/n,
E03690,SantheVicentedel Raspeig,
Spainlaboratory for the study of high-mass star evolution,
Context. The young massive cluster Westerlund
1 o↵ers
promiseof a grand6
Centro de Astrobiología, CSIC-INTA. Campus ESAC. C. bajo del castillo s/n. E-28 692 Villanueva de la Cañada, Madrid, Spainbut its basic parameters are still poorly known.7 Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK2

Xiv:2204.00422v2 [astro-ph.SR] 24 May 2022

rXiv:2204.00422v2 [astro-ph.SR] 24 May 2022

1

Aims. In this paper, we aim at a better characterisation of the cluster by determining some basic kinematic properties and analysing

Westerlund 1
non-parametric

the area surrounding the cluster and the population in its foreground.
Methods. We have used Gaia early data release 3 (EDR3) data, together with spectra of a large
sample of luminous stars in the
ABSTRACT
field surrounding Westerlund 1, to explore the extent of the cluster. We carried out a non-parametric analysis of proper motions andContext.
The young
Westerlund
1 o↵ers
theOB
promisea grandfor themembership determination. We investigated thereddeningand massive
proper cluster
motionsof several
dozen
starsofand
red laboratory
supergiants
lessstudy
thanof high-mass star evolution,
but its basic parameters are still poorly known.
one degree away from Westerlund 1.
Aims. In this paper, we aim at a better characterisation of the cluster by determining some basic kinematic properties and analysing
Results. We identify a population of kinematic
membersof Westerlundthatlargely inincludes
the known spectroscopic members.
the areasurrounding
the cluster and1 thepopulation
its foreground.
From their EDR3 parallaxes, we derive a distanceto theof Gaia
4.23+0.23
kpc.
We
analysetheextinction
direction,
finding
Methods.
Wecluster
have used
early
data
release3(EDR3)
data,
together in
withthis
spectraof a large
sample of luminous stars in the
0.21
field
surrounding
Westerlund
1, to explore
the toextentthe cluster.
We carriedwith
out athenon-parametricanalysis of proper motions andthat it increases by a large amount around 2.8
kpc,
which inall likelihood
is duedarkof clouds
associatedScutum-Crux
membership
determination.
We
investigatedthereddeningandpropermotionsofseveral
dozen
OB
stars
arm. As a consequence, we hardly see any stars at distances comparable (or higher) than that of the cluster. The proper motions ofand red supergiants less than
one degree away from Westerlund 1.
Westerlund 1, however, are very similar to thoseof stars in the field surrounding it which are – almost without exceptionincludes– less distant,
Results. We identify a population of kinematic members of Westerlund 1 that largely
the known spectroscopic members.
+0.23
but distinct. We find a second, astrometricallywell-defined
population
the aforeground(dcluster⇡ 2 kpc),⇠We80analyseaway,thewhichis in this direction, finding
From
their EDR3 parallaxes,
we inderivedistance to theof 4.23centred
kpc.
extinction
0.21
likely connected to the possible open clusterthat
BHit 197.
Westerlund
1 is very
elongated,an e↵ectseemsisreal
andnotdrivenby with the Scutum-Crux
increasesby a large amountaround
2.8 kpc, which
in allthat
likelihood
due todark
cloudsassociated0 higher) than that of the cluster. The proper motions ofarm.WeAs finda consequence,
we hardly
any stars attodistances
comparable(orthe very heavy extinction to the east and south.
a low-density
haloseeextending
distances
up to 10from the cluster centre,
Westerlund
1,
however,areverysimilar
to
those
of
stars
in
the
field
surrounding
whichvariable
are – almost
without exception – less distant,mainly in the north-west quadrant. A few OB stars at larger distances from the cluster, most notably the luminousit blue
(LBV)
but distinct. We find a second, astrometrically well-defined population in the foreground (d ⇡ 2 kpc), centred ⇠ 80 away, which is
MN48, share its proper motions, suggesting that
Westerlund 1 has little or no peculiar motion with respect to the field population of
likely connected to the possible open cluster BH 197. Westerlund 1 is very elongated, an e↵ect that seems real and not driven by
the Norma arm. Despite this, we are unablethe
to veryfindheavy
any extinction
red supergiant
thatandcould
an extended
to the east
south.belong
We findto
a low-density
halopopulation
extending to related
distancesto
up theto 100 from the cluster centre,
cluster, although we observe several dozen suchobjectsin the foreground,demonstrating
thedistancesrichnessfromof thefield population
mainlyin the north-west
quadrant. A few
OB stars at larger
the cluster,
most notably along
the luminous blue variable (LBV)
MN48,
share its propersuggestingthat byWesterlund
has little
or no peculiar
with respect
this sightline. We find a substantial populationof luminous
OB motions,members
obscured
several 1more
magnitudes
of motion
extinction
than to the field population of
the
Norma
arm.
Despite
this,
we
are
unable
to
find
any
red
supergiant
that
could
belongtoanextendedmost known members. These objects, mostly located in the central region of the cluster, increase the population of OB supergiants by population related to thecluster, although we observe several dozen such objects in the foreground, demonstrating the richness of the field population along
about 25%.
this sightline. We find a substantial population of luminous OB members obscured by several more magnitudes of extinction than
Key words.

most known members. These objects, mostly located in the central region of the cluster, increase the population of OB supergiants by

open clusters and associations:individual: Westerlund 1 – stars:evolution – stars: early-type – supergiants – stars:
about 25%.
fundamental parameters

1. Introduction

Key words.

open clusters and associations: individual: Westerlund 1 – stars:evolution – stars: early-type – supergiants – stars:
fundamental parametersstellar systems in the cluster that rare evolutionary phases are
systemsinteractionin the cluster
rare evolutionary phases are
sampled, and di↵erent avenuesstellar
for binary
arethatprobed,sampled,anddi↵erent
avenuesforbinaryWesterlund 1 (Wd 1) is believed to be the most massive young resulting in a variety of outcomes(see, e.g. Clark et al. 2011). interaction are probed,
Westerlund 1 (Wd 1) is believed to be the most massive young
1. Introduction

2022. The Author(s). Published by the American Astronomical Society.
Shanghai Key© Laboratory
for Astrophysics, Shanghai Normal University, 100 Guilin Road, Shanghai 200234, Peopleʼs Republic of China
3
Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001, USA
4
Department of Astronomy and Planetary Science, Northern Arizona University, Flagstaff, AZ 86011, USA
5Morphology
of OpenClustersin theSolarwith Gaia
EDR
3. II.
School 3Dof Physics
and Astronomy,
Sun Yat-sen
University,
Daxue
Road,Neighborhood
Zhuhai, 519082, Peopleʼs
Republicof China
6
HierarchicalStar
Formation
RevealedbySpatialand
Kinematic
Substructures
Center for Astro, Particle and Planetary Physics (CAP3), New York University Abu Dhabi, Abu Dhabi, United Arab Emirates
7
INFN- Sezione
di Padova,
Via Marzolo
8, I35131 Padova,
Italy
1,2
3,4
Xiaoying
Pang 2022, Shih-Yun
Tangrevised, Yuqian
Li1, Zeqiu
Yu1 , Long
Wang5 , Jiayu Li1 , Yezhang Li16 , Yifan Wang1 ,Received
March 26;2022 April
12; accepted2022
1
1
6,7 April 12; published 2022 June
1
1

Yanshu Wang

, Teng Zhang, Mario Pasquato, and M. B. N. Kouwenhoven

Department of Physics, Xi’an Jiaotong-Liverpool University, 111 Ren’ai Road, Dushu Lake Science and Education Innovation District, Suzhou 215123, Jiangsu
Province, Peopleʼs Republic of China; Xiaoying.Pang@xjtlu.edu.cn
2
Shanghai Key Laboratory for Astrophysics, Shanghai Normal University, 100 Guilin Road, Shanghai 200234, Peopleʼs Republic of China
3
Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001, USA
4
Department of Astronomy and Planetary Science, Northern Arizona University, Flagstaff, AZ 86011, USA
5
School of Physics and Astronomy, Sun Yat-sen University, Daxue Road, Zhuhai, 519082, Peopleʼs Republic of China
6Center for Astro, Particle and Planetary Physics (CAP3), New York University Abu Dhabi, Abu Dhabi, United Arab Emirates
7
INFN- Sezione di Padova, Via Marzolo 8, I35131 Padova, Italy
Received 2022 March 26; revised 2022 April 12; accepted 2022 April 12; published 2022 June 6

Abstract

We identify members of 65 open clusters in the solar neighborhood using the machine-learning algorithm StarGO
based on Gaia EDR3 data. After adding members of 20 clusters from previous studies we obtain 85 clusters, andstudy their morphology and kinematics. We classify the substructures outside the tidal radius into four categories:
ﬁlamentary (f1) and fractal (f2) for clusters <100 Myr, and halo (h) and tidal tail (t) for clusters >100 Myr. The
kinematical substructures of f1-type clusters are elongated;
Abstractthese resemble the disrupted cluster Group X.
Kinematic tails are We
distinctin
t-typeclusters,
especially
Pleiades.
We identify
29 hierarchicalgroupsin four young
identify members of 65 open clusters in the solar neighborhoodusing the machine-learningalgorithm
StarGOon Gaia
data.
adding10
membersof 20
clusters
previous
we obtain groups
85 clusters,
and ﬁlament
regions (Alessi 20, based
IC 348,LPEDR32373,
LPAfter2442);
among
these
arefromnew.
Thestudies
hierarchical
form
study
their
morphology
andkinematics.
Weclassify
thesubstructures
outsidethetidal
radiusinto
fourcategories:
networks. Two regions(Alessi 20, LP 2373) exhibit global orthogonal expansion (stellar motion perpendicular toﬁlamentary (f1) and fractal (f2) for clusters <100 Myr, and halo (h) and tidal tail (t) for clusters >100 Myr. The
the ﬁlament), which
mightcomplete
dispersal.
ﬂows(stellarﬁlament)
arekinematical cause
substructuresof f1-typeclusters Infalling-likeare elongated; theseresemblethe motion
disrupted alongcluster theGroup
X.
Kinematictails
aredistinctin
t-typeclusters,
especially
Pleiades.
We
identify
29
hierarchicalgroups
in
four
young
found in UBC 31 and related hierarchical groups in the IC 348 region. Stellar groups in the LP 2442 region
regions (Alessi 20, IC 348, LP 2373, LP 2442); 10 among these are new. The hierarchical groups form ﬁlament(LP 2442 gp 1–5) are
spatially well mixed but kinematically coherent. A merging process might be ongoing in the
networks. Two regions (Alessi 20, LP 2373) exhibit global orthogonal expansion (stellar motion perpendicular to
LP 2442 subgroups.theFor
younger(30
Myr),
the meanaxis ratio,mass,along
and thehalf-mass–radiustend
ﬁlament),
whichsystems
might cause
complete
dispersal.
Infalling-likeﬂowscluster(stellar motion
ﬁlament) are
found
in
UBC
31
and
relatedhierarchicalgroups
in
the
IC
348
region.
Stellargroups
in
the
LP
2442
regionto increase with age values. These correlations between structural parameters may imply two dynamical processes(LP 2442 gp 1–5) are spatially well mixed but kinematically coherent. A merging process might be ongoing in theoccurring in the hierarchicalformation scenario in young stellar groups: (1) ﬁlament dissolution and (2) subgroup
LP 2442 subgroups. For younger systems (30 Myr), the mean axis ratio, cluster mass, and half-mass–radius tend
mergers.
to increase with age values. These correlations between structural parameters may imply two dynamical processes
occurring in the hierarchical formation scenario in young stellar groups: (1) ﬁlament dissolution and (2) subgroup

Uniﬁed Astronomymergers.
Thesaurus concepts: Open star clusters (1160); Young star clusters (1833); Stellar kinematics(1596); Thesaurus
Astrostatistics(1608); Stellar dynamics
Uniﬁed Astronomy
concepts:(1882)
Open star clusters (1160); Young star clusters (1833); Stellar kinematics
Stellardynamics(1596);
Astrostatistics(1882)(1608);
Supporting material: machine-readable table
Supporting material: machine-readable table

1. Introduction1. Introduction
Stars are formed in molecular clouds where the environment
Stars are formed inismolecular
clouds where the environment
compacted with dense gas (Lada & Lada 2003). When theis compacted with dense
gas
(Lada
& Lada2003).
When
the thegravitational force insidemolecular
cloudsovercomes
internalpressure
after
the
cloud
cools
down,
the
gas
starts to
gravitational force

collapse and form stars. This contraction process can result in
the formation of ﬁlaments that form a network feeding newmaterials into hubs at the intersections (Schneider et al. 2010;
Krause et al. 2020). This mass transfer along the ﬁlaments isreferred to as conveyor belt (Longmore et al. 2014; Krumholz

hub regions to broader and lower-density ﬁlamentary networks(Treviño-Morales et al. 2019). The aforementioned observational results indicate a need for improvement of the monolithic
cluster formation mechanism (Lada et al. 1984). In themonolithic cluster formation scenario, star clusters were ﬁrst
born in the central densest region of molecular clouds. After aviolent gas expulsion, stars in the dense clusters will expand
and eventually disperse into the ﬁeld, i.e., the infant mortality(Lada & Lada 2003).
To explain the star formation taking place in the hierarchicalinterstellar medium, Kruijssen (2012) developed the theoretical