Star Formation Newsletter#353 15-21
Yusuke Aso (KASI)

and that the gas is adiabatice the mean molecularweights change,
to be 2.3wemHassumenearly isothermal
dreds
cold and warm
respectively,
wherewith gases,
the speciﬁcheat ratio,
γ =m1.05.
Then we can use theHssure
ass of a hydrogenatom. The assumed Cloudlet
mean
Capture Model for Asymmetric Molecular Emission Lines Observed in TMCenergy conservationn thehtmeans that the cloud gas is molecular while
1A with ALMAdeliss atomicand neutral.¶ Both
the
cold
and
warm
(rE ) +  · [(rE + P) v] = - rv · F , Tomoyuki(4Hanawa)
1, Nami Sakai2 , and Satoshi Yamamoto3
tio
1¶t their thermal timescales
heiristemperatures since
Center for Frontier Science, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan; hanawa@faculty.chiba-u.jp
2cs
the the dynamical one. In order to mimic the
RIKEN Cluster for Pioneering Research, 2-1 Hirosawa, Wako-shi, Saitama 351-0198, Japanr than3v·v
PDepartment of Physics, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
eases
E=
+
,
(5 )
Received 2021 December 10; revised 2022 May 6; accepted 2022 May 6; published 2022 June 23alchange, we assume
that thegas isØ
2 adiabatic(g - 1 ) rkbut
ﬁc heat ratio, γ = 1.05. Then we can use the
Abstractn theØ Class
II in the pressure.
ation
to follow
the change
TMC-1Aisaprotostellar
sourceharboringayoung
protostar, IRAS 04365+2353, and shows highly asymmetricn ourWecolor ﬁeld,
Ø introduce a TMC1A
CS,emission
SO is much stronger in the CSfeatures of a few 100 au scale in its molecular emission lines. Blueshifted+  · [(rE + P ) v] = - rv · F ,(4) (J = 5–4) line than redshifted emission. This asymmetry can be explained if the gas accretion is episodic and takes
metryØΜ* the) form of cloudlet capture, given that the cloudlet is approaching C18O
toward us. The gravity of the protostar⎧1 (cloudlet
transforms
thecloudletintoastreamandchanges
its
velocityalong
theﬂow. The emission from the cloudlet
ption v · vgas). be blueshifted before the(6periastron,)c = 0 (warm should
P
while
it
shouldberedshifted
after
the periastron. If a major part of
E=
+
,
(5 )
⎨
This
cloudlethas not reached the periastron, the former should be dominant. We perform hydrodynamical simulations to
(
)
1
gas
disk
2
(
g
1
)
r
⎩
Ø
often
examine the validity of the scenario. Our numerical simulations can reproduce the observed asymmetry if the orbit
the cloudlet is inclined to the disk plane. The inclination can explain the slow infall velocity observed in thedisks in thetopressure.
hange
trace
the cloudlet and gas disk. ofThecolor (scalar) ﬁeld isØC18O (J = 2–1) line emission. Such episodic accretion may occur in various protostellar cores since actual clouds
e aSO
color ﬁeld,
traced by
could have inhomogeneous density distributions. We also discuss the implication of the cloudlet capture on
observations of related objects.
016).
(
)
1
cloudlet¶erved ⎧(cr ) +  · (crvUniﬁed) = 0.Astronomy Thesaurus concepts:(7) Protostars (1302); Interstellar medium (847); Interstellar molecules (849);
Youngstellarobjects(1834);
Star
formation (1569)
(
)
0
warm
gas
(
)
.
6
c
=
¶t
plane
⎨
Supporting
material:
animations)
gasusediskcylindricalcoordinates,j, 20z), in our computation.
⎩- 1 (WeThe AstrophysicalJournal, 932:122(14pp), 2022(r,JuneHanawa, Sakai, & Yamamotomodel
We
locatetheprotostarattheorigin,
r
=
z
=
0.
We
also
use
the
udlet
disk. The color (scalar) ﬁeld isrecognition, Dullemond et al. (2019) have proposed that the gas
1. Introductionon
3. and gas
Table(x1, y , z ) = (r cos j , r sinc (r ) r (r )j, z ) in our
Cartesian coordinates(X , Y disks,, V ) = accretion is sporadic in the late stage of star formation and that
Young stellar objects often show signatures ofSrotating
, and
Model
Parameterspresentation. For simplicity, we
ignore the self-gravity of thesomec > 0 Class
2pIIsobjects have secondary disks formed by theand their formation is an integral part of star formation. The
captureofa cloudlet (see also Küffmeier et al. 2020). Moreabcd consider ae cloudlet¶Model gas. rThis
simpliﬁcationisjustiﬁed
since
we
rdisksac symmetricψaroundare roughly
the rotation axis, though2cc(cr ) +  · out(cr−4v) = 0. zout(
7)
recently,
Küffmeieral. V(2021)
made numerical−2v (r ) · net3 Ø⎫ dshave
⎧
some
of
them
have
spiralsandother
substructures
(see,
e.g.,
M
and
gas
disk
of
<10
M
.
Then
the
gravitaof
10
⎡
⎤
e
e
(28outer) disk´exp,¶Atsimulations
in
which
the
captured
cloud
forms
an
624 au246 au500Andrews
au100
au Sakai et0°al. 2019; Nakatani et al. 2020).
et al.
2018;⎬⎨
2s 2 inner ⎦⎣tionalpotentialisexpressedassurroundingapreexisting
disk.
⎭
⎩
Ø
1254 (r,au j, z),246
au computation.
1000
au we often100
au implicitly
0° that they are almost symmetricA¢ coordinates,Thus,
assumedricalin our
The argument by Dullemond et al. (2019) is supported by thefrombirth.
However,someyoungstellar objects show highly r = Xn + Yn + sn ,
B
624
au
392
au
500
au
100
au
30°
GMWe also use the(29rotostar at the origin, r =⎧z-= 0.
2
2
2
large
observed
in some sources suchas)AB Aur
1arc-like feature2
3
Ø(rfeatures) to high-resolution molecular line
+auz according a 30°asymmetricC
775 au
535
au
500
au
200
2
2
(Fukagawaetal.
2004).
Theirhydrodynamical
simulations+ z j , z ) in(x, y, z ) =F(r=cos j, rr sin
ourdinatesdricalobservations
with the Atacama Large Millimeter/submillimeter(8) V, κ0, and σ denoteD
775 au
336
au
500
au
200 au0°
wherethetheradialvelocity,
the opacity
reproducearc-likefeature. Their
model is at
antheinterestingGM
Array(ALMA;
see,2 e.g., Yen
et al. 2014, Sakai et al.
2016,
orTheysimplicity, we ignore⎨theself-gravity
of
the
2
2
2
2
2
- 2a3 (3a - r Pineda- z )et (al.r 2020,+ zand<Artura ) ,de la Villarmois
idea
to
be
examinedfurther,thoughthearc-likefeatureline center,
andfor velocity dispersion, respectively. We assume may be
et al. 2019,is justiﬁed since⎩we consider a cloudletØproduced by another mechanism such as Rossby wave
ofﬁcation
theNotes.
L1489, TMC-1A, Per-emb-2, and GSS30-IRS5,
respectively),−2
Figure 7 gives
view of model B at t = 1397 yr andσ = 0.153
km s−1 to instability
be slightly
thanthea zoom-in
velocity(Mirandasmaller
et al. 2016).
nd
gas
disk
of
<10
M
.
Then
the
gravitaa
t = 1860 yr. The cloudlet is stretched by the tidal force to haveelatterThe outerC
evenofthoughthey are not close
In addition, nonaxisymwhere
andcomputationa denote domain.
the mass
the protostar
and binaries.
the length
radius Mof the
−1
a
tail.
The
collisionofthecloudletinducesa spiralCaptureofacloudlet
may
take
place
in
an
earlierstageof wave in the
resolutionof thethat we obtainb
isexpressed
as of the computation domain. metric distribution of the infalling gas aroundthe protostar
is observation (0.4 km s ) so
The impact is clearly seen in the left panel of Figure 7. At
ation
The halfscale,heightstar formation. A few years disk.
earlierthanDullemondetal.
respectively.
The
mass
of
the
protostarisuncertainandthe same time, the density is increased by the strike and aoften suggested from the asymmetry ofsmooth
spectral line
proﬁles,maps. The intensity is evaluatedcchannelto be wasThereported
fractionof the disk is shaved.
cloudlet breaks(2019), an asymmetric molecular
distribution
inthe disk andradial distanceof thecloudlet.
hnicalGMThe initial
althoughitisspatially
unresolved(e.g.,
L483
and
B335,
for
Oya
2
2
2
different
valuesareadoptedintheliterature(0.68.
0.4,
and
0.25
goes through the disk’s midplane. The periastron of the
d
(
)
+
r
z

a
the
prestellar
source
TMC-1A(Sakaietal.
2016).
TMC-1A,cloudletislocatedunderthemidplane.
The
cloudletgas returns
The
initialradiusofthecloudlet.
et al. 2017 and Imai et al. 2019, respectively). MoreI (Xrecently,, Y , V ) =which
I0 {1 harbors- expthe[ -Classt (X I, protostar
Y , toVthe)]}, side of 04365+2535,(30) isperiastron.
r 2e + z 2
upperdisk after the passage ofThe
Me in Aso et al. 2015, BjerkeliIRASa(8et) al. 2016, and Sakai et al.
The Astrophysical Journal, 932:122 (14pp), 2022 June 20

Hanawa, Sakai, & Yamamoto

Figure 5. The same as Figure 1 but for model A¢ at 3784 and 4202 yr.

ò

Figure 6. The left panel shows the initial gas distribution in model B while the right panel denotes that at t = 1311 yr. The animation shows the evolution of thedensity distribution in model B from t = 0 to 2831 yr.
(An animation of this ﬁgure is available.)

Figure 8 employs the Cartesian coordinates, (x ¢ , y¢ , z ), wherex ¢ = x cos 37 . 5 + y sin 37 . 5,(33)

y¢ = - x sin 37 . 5 + y cos 37 . 5,(34)

to avoid degeneracy of the axes on the ﬁgure. Thus, the crosssections denote the gas distribution in the plane of x ¢ = 0 andy¢ = 0. The viewing angle is speciﬁed by i = 55°, jobs = 50°,and χobs = 20°. We use the same viewing angle in the Mockobservation shown in Section 4. As shown in the panel, gas is

Cloudlet Capture Model for Asymmetric Molecular Emission Lines Observed in TMC1A with ALMA
1

Tomoyuki Hanawa1, Nami Sakai2, and Satoshi Yamamoto3

Center for Frontier Science, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan; hanawa@faculty.chiba-u.jp
2
RIKEN Cluster for Pioneering Research, 2-1 Hirosawa, Wako-shi, Saitama 351-0198, Japan3
Department of Physics, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
Received 2021 December 10; revised 2022 May 6; accepted 2022 May 6; published 2022 June 23

Abstract
TMC-1A is a protostellar source harboring a young protostar, IRAS 04365+2353, and shows highly asymmetricfeatures of a few 100 au scale in its molecular emission lines. Blueshifted emission is much stronger in the CS(J = 5–4) line than redshifted emission. This asymmetry can be explained if the gas accretion is episodic and takes
the form of cloudlet capture, given that the cloudlet is approaching toward us. The gravity of the protostar
transforms the cloudlet into a stream and changes its velocity along the ﬂow. The emission from the cloudletshould be blueshifted before the periastron, while it should be redshifted after the periastron. If a major part ofcloudlet has not reached the periastron, the former should be dominant. We perform hydrodynamical simulations to
examine the validity of the scenario. Our numerical simulations can reproduce the observed asymmetry if the orbitof the cloudlet is inclined to the disk plane. The inclination can explain the slow infall velocity observed in the
C18O (J = 2–1) line emission. Such episodic accretion may occur in various protostellar cores since actual clouds
could have inhomogeneous density distributions. We also discuss the implication of the cloudlet capture on
observations of related objects.
Uniﬁed Astronomy Thesaurus concepts: Protostars (1302); Interstellar medium (847); Interstellar molecules (849);
Young stellar objects (1834); Star formation (1569)
Supporting material: animations
1. Introduction

components of the CS map (7.56–9.16 km s−1), which is also

Young stellar objects often show signatures of rotating disks,
and their formation is an integral part of star formation. The
disks are roughly symmetric around the rotation axis, thoughsome of them have spirals and other substructures (see, e.g.,Andrews et al. 2018; Sakai et al. 2019; Nakatani et al. 2020).
Thus, we often assume implicitly that they are almost symmetricfrom birth. However, some young stellar objects show highly
asymmetric features according to high-resolution molecular line
observations with the Atacama Large Millimeter/submillimeter
Array (ALMA; see, e.g., Yen et al. 2014, Sakai et al. 2016,
Pineda et al. 2020, and Artur de la Villarmois et al. 2019, for
L1489, TMC-1A, Per-emb-2, and GSS30-IRS5, respectively),
even though they are not close binaries. In addition, nonaxisymmetric distribution of the infalling gas around the protostar isoften suggested from the asymmetry of spectral line proﬁles,although it is spatially unresolved (e.g., L483 and B335, for Oya
et al. 2017 and Imai et al. 2019, respectively). More recently,

The disk rotation assimilates the loss and is weaker in modelrecognition, Dullemond et al. (2019) have proposed that the gas
accretion is sporadic in the late stage of star formation and thatsome Class II objects have secondary disks formed by thecapture of a cloudlet (see also Küffmeier et al. 2020). Morerecently, Küffmeier et al. (2021) have made numericalsimulations in which the captured cloud forms an outer disk
surrounding a preexisting inner disk.
The argument by Dullemond et al. (2019) is supported by thelarge arc-like feature observed in some sources such as AB Aur(Fukagawa et al. 2004). Their hydrodynamical simulations
reproduce the arc-like feature. Their model is an interestingidea to be examined further, though the arc-like feature may be
produced by another mechanism such as Rossby wave
instability (Miranda et al. 2016).
Capture of a cloudlet may take place in an earlier stage ofstar formation. A few years earlier than Dullemond et al.
(2019), an asymmetric molecular distribution was reported in
the prestellar source TMC-1A (Sakai et al. 2016). TMC-1A,
which harbors the Class I protostar IRAS 04365+2535, is a

Unveiling the outer dust disc of TW Hya with deep ALMA observations
John D. Ilee ,1 Catherine Walsh,1 Jeff Jennings ,2 Richard A. Booth ,3 Giovanni P. Rosotti ,4,5
Richard Teague ,6 Takashi Tsukagoshi7 and Hideko Nomura8
1 School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK

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

3 Astrophysics Group, Imperial College London, Blackett Laboratory, Prince Consort Road, London SW7 2AZ, UK
4 School of Physics & Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK
6 Center for Astrophysics | Harvard & Smithsonian, 60 Garden St., Cambridge, MA 02138, USA

7 Division of Radio Astronomy, National Astronomical Observatory of Japan, Osawa 2-21-1, Mitaka, Tokyo 181-8588, Japan
8 Division of Science, National Astronomical Observatory of Japan, Osawa 2-21-1, Mitaka, Tokyo 181-8588, Japan

Accepted 2022 April 29. Received 2022 April 26; in original form 2021 December 17

ABSTRACTThe radial extent of millimetre dust in protoplanetary discs is often far smaller than that of their gas, mostly due to processes suchas dust growth and radial drift. However, it has been suggested that current millimetre continuum observations of discs do not
trace Unveilingtheir full extent
due todust
limitedIn thisL25
letter, we present deep (19 µJy beam−1 ) moderate resolution (0.37 arcsec)
the outerdiscsensitivity.
of TW Hya
ALMA observations at 1 mm of the nearest protoplanetary disc, TW Hya. Using the visibility analysis tool frank, we reveal astructured millimetre intensity distribution out to 100 au, well beyond previous estimates of 60–70 au. Our analysis suggests thepresence of a new millimetre continuum gap at 82 au, coincident with similar features seen in optical/near-infrared scattered lightand millimetre molecular line observations. Examination of the fit residuals confirms the presence of the previously reported
au-scale continuum excess at 52 au (P.A. = 242.5◦ ). Our results demonstrate the utility of combining deep, moderate-resolution
observations with super-resolution analysis techniques to probe the faintest regions of protoplanetary discs.
Key words: techniques: interferometric – protoplanetary discs – stars: individual: TW Hya – submillimetre: planetary systems.

1 I N T RO D U C T I O N
Observations of planet-forming discs have shown that the radialextent of their millimetre dust component is, generally, smaller thanthe extent of molecular gas in the disc (e.g. Panić et al. 2009; Andrews
et al. 2012). Initially, this difference was attributed to limited
sensitivity (see Dutrey et al. 1998), but further observations revealed
that the gas and dust cannot be reproduced with the same surface
density profile (Hughes et al. 2008). In particular, observations
with the Atacama Large Millimetre/submillimetre Array (ALMA)
demonstrated that a sharp decrease in dust surface at the outer edge
is required (e.g. de Gregorio-Monsalvo et al. 2013; Andrews et al.
2016).

(Birnstiel & Andrews 2014). However, observed continuum fluxes
and radial extents suggest that drift needs to be halted (or significantly
slowed) in the majority of discs (Pinilla et al. 2012). This can beachieved via local pressure maxima induced by substructure in discs,
e.g. rings and gaps (see Andrews 2020).
Despite this apparently self-consistent picture, Rosotti et al. (2019)suggested that even the most recent observations of the millimetre
dust continuum in discs are still limited by sensitivity. In contrast toBirnstiel & Andrews (2014), they argue that currently measured discradii do not trace the sharp outer edge in the dust distribution, butrather the radius out to which the grains are large enough to possess
significant (sub-)millimetre opacity. The dust surface density extends
further, but in these regions the grains are small and the opacity

Downloaded from https://academic.oup.com/mnrasl/article/515/1/L23/6609934 by DANKOOK UNIV user on 29 July 20

5 Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The NetherlandsUnveiling the outer dust disc of TW Hya with deep ALMA observations
John D. Ilee ,1 Catherine Walsh,1 Jeff Jennings ,2 Richard A. Booth ,3 Giovanni P. Rosotti ,4,5
Richard Teague ,6 Takashi Tsukagoshi7 and Hideko Nomura8
1 School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK

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

3 Astrophysics Group, Imperial College London, Blackett Laboratory, Prince Consort Road, London SW7 2AZ, UK
4 School of Physics & Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK
6 Center for Astrophysics | Harvard & Smithsonian, 60 Garden St., Cambridge, MA 02138, USA

7 Division of Radio Astronomy, National Astronomical Observatory of Japan, Osawa 2-21-1, Mitaka, Tokyo 181-8588, Japan
8 Division of Science, National Astronomical Observatory of Japan, Osawa 2-21-1, Mitaka, Tokyo 181-8588, Japan

Accepted 2022 April 29. Received 2022 April 26; in original form 2021 December 17

Unveiling the outer dust disc of TW Hya
ABSTRACTThe radial extent of millimetre dust in protoplanetary discs is often far smaller than that of their gas, mostly due to processes suchas dust growth and radial drift. However, it has been suggested that current millimetre continuum observations of discs do not
trace their full extent due to limited sensitivity. In this letter, we present deep (19 µJy beam−1 ) moderate resolution (0.37 arcsec)
ALMA observations at 1 mm of the nearest protoplanetary disc, TW Hya. Using the visibility analysis tool frank, we reveal astructured millimetre intensity distribution out to 100 au, well beyond previous estimates of 60–70 au. Our analysis suggests thepresence of a new millimetre continuum gap at 82 au, coincident with similar features seen in optical/near-infrared scattered lightand millimetre molecular line observations. Examination of the fit residuals confirms the presence of the previously reported
au-scale continuum excess at 52 au (P.A. = 242.5◦ ). Our results demonstrate the utility of combining deep, moderate-resolution
observations with super-resolution analysis techniques to probe the faintest regions of protoplanetary discs.
Key words: techniques: interferometric – protoplanetary discs – stars: individual: TW Hya – submillimetre: planetary systems.

1 I N T RO D U C T I O N
Observations of planet-forming discs have shown that the radialextent of their millimetre dust component is, generally, smaller thanthe extent of molecular gas in the disc (e.g. Panić et al. 2009; Andrews
et al. 2012). Initially, this difference was attributed to limited
sensitivity (see Dutrey et al. 1998), but further observations revealed
that the gas and dust cannot be reproduced with the same surface
density profile (Hughes et al. 2008). In particular, observations
with the Atacama Large Millimetre/submillimetre Array (ALMA)
demonstrated that a sharp decrease in dust surface at the outer edge
is required (e.g. de Gregorio-Monsalvo et al. 2013; Andrews et al.
2016).

(Birnstiel & Andrews 2014). However, observed continuum fluxes
and radial extents suggest that drift needs to be halted (or significantly
slowed) in the majority of discs (Pinilla et al. 2012). This can beachieved via local pressure maxima induced by substructure in discs,
e.g. rings and gaps (see Andrews 2020).
Despite this apparently self-consistent picture, Rosotti et al. (2019)suggested that even the most recent observations of the millimetre
dust continuum in discs are still limited by sensitivity. In contrast toBirnstiel & Andrews (2014), they argue that currently measured discradii do not trace the sharp outer edge in the dust distribution, butrather the radius out to which the grains are large enough to possess
significant (sub-)millimetre opacity. The dust surface density extends
further, but in these regions the grains are small and the opacity

Downloaded from https://academic.oup.com/mnrasl/article/515/1/L23/6609934 by DANKOOK UNIV user on 29 July 20

5 Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands

L27

Fevering Interstellar Ices Have More CH3OD
arXiv:2204.01035v1 [astro-ph.GA] 3 Apr 2022

Table 1: Initial atomic abundances at the start of the calculations relative to nH .
∗,††‡Beatrice
M. Kulterer,
2.2.1
Model 1 Maria N. Drozdovskaya, Stefano Antonellini, Catherine
Species n(X)Walsh,¶ andTom
J.−5Millar§
H
5.00
×
10
The chemical network, denoted as Model 1, includes ∼ 29 200 reactions and 1 170 species.
H2 + + 5.00 × 10−1Withthe exception
ofHe
HD2CH3OH,D
D2, andDBern,
O, onlymono-deuterated
are included,
ØCOMs 6,species
3 ,9.75
2−2†Centerfor Spaceand Habitability,
University
Gesellschaftsstrasse
3012 Bern,×of10
Ø <20 KD
DC isotopologues
1.40 × could
10−4theoretically be formed. The main methanol
even if multiply deuterated
Switzerland
3.20CH2DOH/CH3OD
× 10−4Ø
CH3‡Institut
OHde Radioastronomie
D(CH3OH)Oin theisotopologue
solid
phase
predominately
forms via subsequent addition of hyS Millimétrique
8.00 ×(IRAM),10−8 300 rue de la piscine, F-38406
drogen atoms to CO inSithis
network.
experiments 17,18 have shown that methanolSaint-Martind’Hères,
8.00Laboratory× 10−9FranceØP
3.00
× 10−9 of COLeeds,
formation
via thehydrogenationices atLS2
temperatures¶Schoolof occurs
Physicsefficiently
and Astronomy,
University of Leeds,
9JT, UK in the range−9
Ø UMIST Database for Astrochemistry Cl RATE12
D4.00 × 10of ∼ 10–12
K with Centre,
H2F
CO as
an intermediate:§Astrophysics
Research
Schoolof Mathematics
2.00
× 10−8 and Physics, Queen’s University
10−9 BT7 1NN, UK
Belfast,Fe
University3.00
Road,×Belfast−9
Na HCO −→
2.00
× 10
CO
−→
H
CO
−→
CH3O, CH2OH −→ CH3OH.
(1)
2
Model 1: H, D
D
−9
Mg
7.00
×
10
E-mail: beatrice.kulterer@unibe.ch
Model 2A: H, D
DHD
1.60 × 10−5

Model 2B: CO+H à HCO

These experiments have confirmed
4 that the majority of methanol that is observed in the ISM
AbstractaTable 2:likely
Investigatedwiththe threechemicalmodels.occurs,
stems from parameter
this reaction spacepathway.
Gas-phaseformationof methanol
but not

Mono-deuterated methanol is thought to form during the prestellar
core stage of star36

efficiently
enough to explain
Parameter
Valuethe observed abundances.

Calculated activation barriers for

5 ratio6 suggest
formation.
Observed variationsin the3ODt(yr)
104 , (1,3,CH
5,2DOH/CH
7.5) × 10, 10 , 107 that its forma-core and third hydrogenation steps of the scheme in Eq. 1 are large (> 2 000 K), 50 therethe first(K)
10,
15,surrounding
20, 25, 30
tion isTstrongly
on thecloud conditions. Thus, it is a potential
dust,gas dependent−3 via quantum tunneling.
forentheyoccur
for6 the formation of CH2OH(cm)
4 × 104 , 105 , 5The× activation
105 , 106 ,barrier
5 × 10H the physical conditions before the onset of star formation. A single-point phystracer of) to be 5more
× 10
CR (s
hasζbeenshown
than a factor of two higher 50,51 and therefore the formation of−1−17

ical model representative of a typical prestellar core is coupled to chemical models to

EA(CO+H) (K)400, 900, 1 400, 2 500

CH3O is more likely. The activation energies are adopted from the kida database 52 and arepotential formation pathways towards deuterated methanol at the prestellar
If multiple investigate
values are
given per parameter, the default value used in the fiducial model
set
to
2
500
K for HCO,
2 200
andable5 400
K for CH2observed
OH formation.
3O, not
stage.
Simple addition
reactions
of K
H for
andCH
D are
to reproduce
abunis indicated inboldface.
aarXiv:2204.01035v1 [astro-ph.GA] 3 Apr 2022

Fevering Interstellar Ices Have More CH3OD
Beatrice M. Kulterer,∗,† Maria N. Drozdovskaya,† Stefano Antonellini,‡ Catherine
Walsh,¶ and Tom J. Millar§†Center for Space and Habitability, University10of Bern,
6,33012
K GesellschaftsstrasseCH
ODBern,CH3O

Switzerland

A CH OHàCH OHàCH DOH
crease the rate of this reaction, and therefore all the relative rates in the abstraction scheme
CH3ODàCHCH3OD
2OD
Saint-Martin d’Hères,Francein Model 2A. The considered grid of gas densities and E is used to investigate variations ofB:
2A
FigureAbundancesof withkey species
towards
the formationof mono-deuterated
the CH 1:
DOH/CHOD ratiothe newly
constructed
Models 2A_CXOX¶Schooland 2A_Song.
ofmethanol
Physics and Astronomy, University of Leeds, Leeds, LS2 9JT, UK
as obtained with Model 1 for a core age of 3 × 10 yrA
and dust temperatures in the range
Ø CH2DOH/CH3OD
Combinedwiththe aforementioned
space
explored
the theoreticalof
10–30 K.
Gaseousspecies are parameter
depicted asdashedlines,bysolidlines refermodellingto grain-surface§Astrophysics
Research
Centre,School of Mathematics and Physics, Queen’s University
species.
HCO these(lightmodels
green)also
andtestDCO
shown
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Theformamiddle panel
work of T12,
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H CO
+ Hin
based
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Belfast,
University
Road,
BelfastBT7 1NN, UK
tion
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OH.
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are
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from
the
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database,andquantumchemical
CH DOH (light blue) and CH OD (dark blue) are shown in the lower panel.
Ø
CO+HàHCO
EA
calculations. Those values were published after Hidaka and colleagues conducted their exlead to a ratio of ∼ 1 at 10 K across the considered core ages, are not sufficient for explaining
EA
periments.
Results for Model 2A_CX OX at 10 K for core ages between 10 –10 yr are
E-mail: beatrice.kulterer@unibe.chthe observed abundances.
EA
Figure 2: Abundances of key species towards the formation of deuterated methanol as obØ CH3OD
tained with Model 2A for a core age of 3 × 10 yr and dust temperatures in the range
Abstractof 10–30 K. Gaseous species are depicted as dashed lines, solid lines refer to grain-surface16Ø⾒species. HCO (light green) and DCO (green)
are shown in the upper panel. The middle
Higher gas densities and lower activation barriers for the CO + H −→HCO reactionin‡Institut
de Radioastronomie
Millimétrique (IRAM),
3 300 rue de2la piscine, F-38406
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CH3OH (blue)
and its is thought to form during the prestellar core stage of star
mono-deuterated isotopologues, CH2DOH (light blue) and CH3OD (dark blue), are shown information. Observed variations in the CH2DOH/CH3OD ratio suggest that its formathe lower panel. Gas-phase abundances of (deuterated) methanol are ≤ 10−11 and therefore
not included in the plot.
tion is strongly dependent on the surrounding cloud conditions. Thus, it is a potential

Ø Orion BN/KLØ
tracer of the physical conditions before the onset of star formation. A single-point physH-D
ical model representative of a typical prestellar core is coupled to chemical models topresetllar
investigate potential formation pathways towards deuterated methanol at the prestellar
Figure 7: Calculated CH2DOH/CH3OD ratios compared with what is expected to be foundinprestellaraddition
cores from observations.
depicted
for a notTdust able
range ofto
10–30
K and
stage.
SimplereactionsValuesof HareandD arereproduce
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a range of gas densities
and activation
5
6
core ages of 10 –10 yr. The blue slope, denoted “addition only” refers to results from Model~1
HDO CH3OH
CH3OD

Expanding shells around young clusters – S 171/Be 59? , ??
G. F. Gahm1, † , M. J. C. Wilhelm2 , C. M. Persson3 , A. A. Djupvik4,5 , and S. F. Portegies Zwart2
1

Stockholm Observatory, AlbaNova University Center, Stockholm University, 106 91 Stockholm, Sweden
Leiden University, PO Box 9500, 2300 RA Leiden, Hollande-mail: wilhelm@strw.leidenuniv.nl
3
Chalmers University of Technology, Department of Space, Earth and Environment, Onsala Space Observatory, 439 92 Onsala,Sweden4
Nordic Optical Telescope, Rambla José Ana Fernández Pérez 7, 38711 Breña Baja, Spain
5
Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000 Aarhus C, Denmark2

Received 16 December 2021 / Accepted 20 April 2022
ABSTRACT

6

Institute for Research
on Exoplanets, Université de Montréal, Département de Physique, C.P. 6128 Succ. Centre-ville, Montréal, QC H3C 3J7, Canada© 2022. The Author(s). Published by the American Astronomical Society.
7Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218, USA
8Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 W. Brooks Street, Norman, OK 73019, USA
Departmentof Computer
Johns Hopkins
University,
USA Reality
Disks in 9Nearby
Young
StellarScience,
AssociationsFound
Via Virtual
10
DepartmentofPhysics,
Emory
University,
201
DowmanDrive,
Atlanta,
GA 30322, USA
11 1,2 , Marc J. Kuchner1 , Steven M. Silverberg3 , Matthew A. Brandt4, Thomas G. Grubb4, Jonathan Gagné5,6 ,Susan Higashio
French National Centre for ScientiﬁcResearch, 3 Rue Michel Ange, 75016 Paris, France
1
John H. Debes7 , Joshua Schlieder, John P. Wisniewski8 , Stewart Slocum9 , Alissa S. Bans10 ,12
Disk
Detective
Citizen Scientist
1112, Joseph R. Biggs, Milton K. D. Bosch12 , Tadeas Cernohous12 , Katharina Doll12 ,13 Shambo Bhattacharjee
12,13 Nacional de Córdoba-CONICET.
12
12 Córdoba, Argentina
IATE-OAC,
Universidad
LapridaX5000
BGR,
Hugo A. Durantini Luca
, Phillip Grifﬁth,
Sr.12854,, Joshua
Hamilton, Jonathan Holden12 ,14 12,14 , Alexandru Enachioaie
1212
12 191-0042,
12 Japan
MeiseiUniversity,
2-1-1
Hodokubo,
Hino,
Tokyo
Michiharu Hyogo, Dawoon Jung , Lily Lau , Fernanda Piñeiro , Art Piipuu , and Lisa Stiller12
Received 2021 December 8; revised 2022
March
17; Collaboration
accepted 2022 April 4; published 2022 June 28
The Disk
Detective
1

NASA Goddard Space Flight Center, Exoplanets and Stellar Astrophysics Laboratory, Code 667, Greenbelt, MD 20771, USA; susan.higashio@gmail.com
2
Center for Research and Exploration in Space Science and Technology, NASA/GSFC, Greenbelt, MD 20771, USA
3
MIT Kavli Institute, USA
4
NASA Goddard Space Flight Center, Science Data Processing Branch, Code 587, Greenbelt, MD, 20771, USA
5
Planétarium Rio Tinto Alcan, Espace pour la Vie, 4801 av. Pierre-de Coubertin, Montréal, Québec, Canada
6
Institute for Research on Exoplanets, Université de Montréal, Département de Physique, C.P. 6128 Succ. Centre-ville, Montréal, QC H3C 3J7, Canada
7Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218, USA
8Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 W. Brooks Street, Norman, OK 73019, USA
9
Department of Computer Science, Johns Hopkins University, USA
10
Department of Physics, Emory University, 201 Dowman Drive, Atlanta, GA 30322, USA
11
French National Centre for Scientiﬁc Research, 3 Rue Michel Ange, 75016 Paris, France
12
Disk Detective Citizen Scientist
13
IATE-OAC, Universidad Nacional de Córdoba-CONICET. Laprida 854, X5000 BGR, Córdoba, Argentina
14
Meisei University, 2-1-1 Hodokubo, Hino, Tokyo 191-0042, Japan
Received 2021 December 8; revised 2022 March 17; accepted 2022 April 4; published 2022 June 28

Abstract
The Disk Detective citizen science project recently released a new catalog of disk candidates found by visualinspection of images from NASA’s Wide-ﬁeld Infrared Survey Explorer mission and other surveys. We applied
this new catalog of well-vetted disk candidates to search for new members of nearby young stellar associations(YSAs) using a novel technique based on Gaia data and virtual reality (VR). We examined AB Doradus, Argus, βPictoris, Carina, Columba, Octans-Near, Tucana–Horologium, and TW Hya by displaying them in VR together
with other nearby stars, color coded to show infrared excesses found via Disk Detective. Using this method allows
us to ﬁnd new association members in mass regimes where isochrones are degenerate. We propose 10 new YSA
members with infrared excesses: three of AB DoradusAbstract(HD 44775, HD 40540 and HD 44510), one of β Pictoris(HD 198472), twoTheof Disk
Octans-Near(HD
157165BD+35
andoffour
membersof a combined
Detective citizen
scienceproject andrecently
released 2953),
a new catalog
disk disk-hosting
candidates found by
visualinspectionofimagesfromNASA’sWide-ﬁeld
Infrared
SurveyExplorermissionandothersurveys.
We
appliedpopulation of Carina,
Columba, and Tucana–Horologium: CPD-57 937, HD 274311, HD 41992, and WISEA
this new catalog of well-vetted disk candidates to search for new members of nearby young stellar associations
J092521.90-673224.8.
appears
to berealityan (VR).
extremedebriswitha βfractional infrared(YSAs) This
using a lastnovel object
technique (J0925)
based on Gaia
data and virtual
We examined
AB disk
Doradus,
Argus,−2Carina, Columba, Octans-Near, Tucana–Horologium, and TW Hya by displaying them in VR together
Pictoris,luminosity of 3.7 × 10 . We also propose two new members of AB Doradus that do not show infrared excesses:with other nearby stars, color coded to show infrared excesses found via Disk Detective. Using this method allows
TYC 6518-1857-1usand
CPD-251292.
We ﬁnd15115
to degenerate.
be a member
of Tucana–Horologium
ratherto ﬁndnew association
members
in massHD
regimes
where appears
isochrones are
We propose
10 new YSA
memberswithinfraredexcesses:
three
of
AB
Doradus(HD
44775,
HD
40540
and
HD
44510),
oneofβ
Pictoristhan β Pictoris. We advocate for membership in Columba–Carina of HD 30447, CPD-35 525, and HD 35841.
(HD 198472), two of Octans-Near (HD 157165 and BD+35 2953), and four disk-hosting members of a combined
Finally, we proposethat ofthreedwarfs,previously consideredof 41992,
Tucana–Horologium
are better
population
Carina,M
Columba,and Tucana–Horologium:
CPD-57 937,members
HD 274311, HD
and WISEA
J092521.90-673224.8.
This
last
object(J0925)appearstobeanextremedebrisdisk
withafractional
infraredconsidered a separate association,−2tentatively called “Smethells 165”.
luminosity of 3.7 × 10 . We also propose two new members of AB Doradus that do not show infrared excesses:

6518-1857-1 concepts:
and CPD-25 1292.
We ﬁndHD 15115
appears
to be a member
of Tucana–Horologium
ratherexcess (788)
Uniﬁed AstronomyTYC
Thesaurus
Debrisdisks(363);
Movingclusters(1076); Infrared
than β Pictoris. We advocate for membership in Columba–Carina of HD 30447, CPD-35 525, and HD 35841.
Finally, we propose that three M dwarfs, previously considered members of Tucana–Horologium are better
considered a separate association, tentatively called “Smethells 165”.

Uniﬁed Astronomy Thesaurus concepts: Debris disks (363); stages,
Moving clusters
Infrared excess(788) time constraints for gas and1. Introductionand (1076);
providingcriticalplanetesimal accretion and orbit evolution (e.g., Mamajek 2009;
Stars in young moving groups and1. Introduction
associations often show
stages,critical time
constraints for manygas and disks with resolved
Mengandetproviding
al. 2017).
Furthermore,
excess emission at infrared(IR)
wavelengths
pointing
totheplanetesimal accretion and orbit evolution (e.g., Mamajek 2009;
Stars in young moving groups and associations often show
images, like β Pictoris, HR 4796A, AU Microscopii, belong to3Institute for Astronomy, School of Physics, Zhejiang University, Hangzhou 310027, China
Center for Star and Planet Formation, GLOBE Institute, University of Copenhagen, Øster Voldgade 5-7, 1350 Copenhagen, DenGrowth after the streaming instability:mark
e-mail: hyerin.jang@astro.ru.nl,bbliu@zju.edu.cn,Anders.Johansen@sund.ku.dk
The radial distance dependence of the planetary growthHyerin Jang1, 2 , Beibei Liu3? , and Anders Johansen4, 2

May 23, 20221

Department of Astrophysics/IMAPP, Radboud University, P.O. Box 9010, NL-6500 GL Nijmegen, The Netherlands
ABSTRACT
Lund Observatory, Department of Astronomy and Theoretical
Physics, Lund University, Box 43, 22100 Lund, Sweden
3
Institute for Astronomy, School of Physics, Zhejiang University, Hangzhou 310027, China
4CenterisforhypothesizedStar and Planet Formation,
GLOBE Institute,
Universityprotoplanetaryof Copenhagen, Øster
Voldgade
5-7, 1350
Copenhagen,Den- density of the
Streaming instability
to be triggeredat particulardisk
locationswherethe volume
marksolid particles is enrichedcomparable to that of the gas. A ring of planetesimals thus forms when this condition is fulfilled locally.
e-mail: hyerin.jang@astro.ru.nl,bbliu@zju.edu.cn,Anders.Johansen@sund.ku.dk
2

v1 [astro-ph.EP] 20 May 2022

3v1 [astro-ph.EP] 20 May 2022

4

These planetesimals collide with each other and accrete inward drifting pebbles from the outer disk to further increase masses. We
May 23, 2022
investigate the growth of the planetesimals that form in a ring-belt at various disk radii. Their initial mass distributions are calculated
based on the formula summarized from the streaming instability simulations. We simulate the subsequent dynamical evolution of the
ABSTRACT
planetesimals with a protoplanetary disk model based either on the minimum mass solar nebula (MMSN) or on the Toomre stability
hypothesized
be triggeredat particular
protoplanetary
disk arelocationswhereatthea volume
density
the0.3 AU, resulting
criterion. For theStreaming
MMSNinstability
model,isboth
pebble toaccretionandplanetesimalaccretion
efficientclose-inorbitof ofsolid
is enrichedcomparable
to thatof the aftergas. A 1
ringof planetesimals
thus forms only
when thisis fulfilled planetesimals
locally.
in the emergenceofparticles
severalsuper-Earthmassplanets
Myr.
For comparison,
thecondition
most massive
undergo
These planetesimals collide with each other and accrete inward drifting pebbles from the outer disk to further increase masses. We
substantial massinvestigate
growth the
when
they
are
born at r=3
AU,inwhiletheatplanetesimals
r=30
littleor no growth. On thegrowthof theplanetesimals
that forma ring-beltvarious disk radii. at
TheirinitialAU
massexperience
distributions arecalculated
basedon theToomre
formula summarized
themassive
streaming instability
We simulate
the subsequent
dynamical
evolutionof the a mass between
other hand, in thedenserdisk, thefrom
mostformingsimulations.
planets canreach Earthmass att=1 Myr
and reachplanetesimals
withaprotoplanetary
disk
model
based
eitherontheminimummass
solar
nebula(MMSN)oronthe
Toomrestabilitythat of Neptune and that of Saturn within 3 Myr at 30 AU and 100 AU. Both the pebble and planetesimal accretion rate decrease with
criterion. For the MMSN model, both pebble accretion and planetesimal accretion are efficient at a close-in orbit of 0.3 AU, resulting
disk radial distance.
planetesimalaccretion
lesspronounced
than only
pebbleaccretion
more distantdisk regions. Taken
in theNevertheless,emergence of several
super-Earth massplanets is
after
1 Myr.
For comparison,
the most
massive atplanetesimals
undergosubstantial
mass higher
growth when
they whenare bornthe
at r=3AU,
while
the planetesimals
at r=30experience
littleor noand/or
growth.aOn
the Stokes number
together, the planets
acquiremassesdisk
hasa highergas density,a AUhigherpebble
flux,
lower
other
hand,
in
the
denserToomre
disk,
the
most
massiveformingplanets
can
reach
Earth
mass
at
t=1
Myr
and
reach
a
mass
betweenof pebbles.
Key words.

1. Introductionthat of Neptune and that of Saturn within 3 Myr at 30 AU and 100 AU. Both the pebble and planetesimal accretion rate decrease withdisk radial distance. Nevertheless, planetesimal accretion is less pronounced than pebble accretion at more distant disk regions. Taken
numerical– planets and satellites: formation
together, the planets acquire higher masses when the disk has a higher gas density, a higher pebble flux, and/or a lower Stokes numberof pebbles.
Key words. numerical – planets and satellites: formationa size distribution of pebbles (Zhu & Yang 2021). Overall, themetallicity
difficultsatisfy
globally
in a canonicalIntroductionto centimeter-sized bodies (named athresholdsize distributionof pebblesis(Zhu& Yangto2021).
Overall,the
The growth of1.millimetersolar-like protoplanetary disk.

4 Astronomical Observatory, University of Warsaw, Al. Ujazdowskie 4, 00-478 Warszawa, Poland

The E↵ect of Molecular Cloud Properties on the Kinematics of Stars Formed in the Trifid Region
1
1
2
1
2
Michael A. Kuhn,
Lynne
A. Hillenbrand,
Eric March
D. Feigelson,
Fowler,Konstantin(Received
January
4, 2022; Revised
14, 2022;Ian
Accepted
March
17, 2022)V. Getman,
Patrick S. Broos,2 Matthew S. Povich,3 and Mariusz Gromadzki4

Submitted to ApJ

1 Department of Astronomy, California Institute of Technology, Pasadena, CA 91125, USA
2 Department of Astronomy & Astrophysics, Pennsylvania State University, 525 Davey Laboratory, University Park, PA 16802, USA

82v2 [astro-ph.GA] 24 Mar 2022

03.07382v2 [astro-ph.GA] 24 Mar 202

3 Department of Physics and Astronomy, California State Polytechnic University, 3801 West Temple Ave, Pomona, CA 91768, USA

ABSTRACT
4 Astronomical Observatory, University of Warsaw, Al. Ujazdowskie 4, 00-478 Warszawa, Poland
The dynamical
states of molecular clouds may a↵ect the properties of the stars they form. In thevicinity of the Trifid Nebula (d = 1180 ± 25 pc), the main star cluster (Trifid Main) lies within an(Received
4, 2022;
RevisedMarch 14,2022;toAccepted
March(Trifid
17, 2022)
expanding sectionof the January
molecular
cloud;
however,⇠0.3
the north
North), the cloud’s
velocity structure is more tranquil. We acquired
ChandraX-ray observation to identify pre-mainSubmitteda to
ApJ
sequence stars in Trifid North, complementing a previous observation of Trifid Main. In Trifid North, we
identified 51 candidate pre-main-sequence stars,of which 13 are high-confidence Trifid members based
ABSTRACTon Gaia
parallaxes
proper clouds
motions.
also
TrifidInMain
TheEDR3
dynamical
states ofandmolecular
may Wea↵ectthere-analyzed
properties ofmembershipthe stars theyofform.
the andseparated
multiplebackgroundstellarassociations.
North (Trifid
represents
stellarpopulation
vicinityoutof theTrifid Nebula(d = 1180± 25pc), the mainTrifid
star cluster
Main)a lies
withinan
expandingof themolecular
cloud; inhowever,⇠0.3 partto the(Trifid The
North),
cloud’s⇠10%
as rich section
as Trifid
Mainthat formed
a separate
of norththe cloud.
1D thestellarvelocity
1velocityinstructure
is moretranquil.km
Wes acquireda Chandra
X-ray
observation
identify
pre-maindispersion
Trifid North(0.6±0.2) is threetimes lower
thanin Trifidto
Main(1.9±0.2
km s 1 ).
sequence stars
in Trifid
North,
complementing
a previous
observationof Trifid
Main.
Trifid North,
we
Furthermore,in Trifid
Main,propermotions indicate
that
the portionof thestarIncluster
superimposed
identified
candidatepre-main-sequencestars, ofof thewhich
13 region
are high-confidence
Trifid members
based andon theoptical51nebula
is expanding.
Expansion
H iiaround the O-star
HD 164492A,
on Gaia EDR3 parallaxes and proper motions. We also re-analyzed membership of Trifid Main andthe resulting gas expulsion, can explain both the motions of the stars and gas in Trifid Main. Contrary
separated out multiple background stellar associations. Trifid North represents a stellar population
to previous
we findnothatevidence
cloud-cloud
collision
triggeredstarformation⇠10% as studies,rich as Trifid
Main
formedthat
in aaseparate
part ofthe cloud.
The 1D
stellarvelocityin theregion.
dispersion in Trifid North (0.6± 0.2 km s 1 ) is three times lower than in Trifid Main (1.9± 0.2 km s 1 ).

3 Department of Physics and Astronomy, California State Polytechnic University, 3801 West Temple Ave, Pomona, CA 91768, USA

Furthermore, in Trifid Main, proper motions indicate that the portion of the star cluster superimposedon theH ii region
around the O-star HD 164492A, andO optical nebula
HII is expanding. Expansion of theTrifid
Main
the resulting
gas expulsion,can explainboththeformation;
motions of thestarskinematics;
and gas in Trifid
Main.
Contrary
Keywords:
Astrometry;
Molecular
clouds;Star
Stellar
X-ray
astronomy
to previous studies, we find no evidence that a cloud-cloud collision triggered star formation in theregion.
1. INTRODUCTION
17 (the Omega Nebula), and 20 (the Trifid Nebula). Nu-

In the vicinity of the Sun, many of the major star-merical galaxy simulations find that filamentary chains