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Spectroastrometric Study of Ro-vibrational CO Emission from the Herbig Ae star HD 179218 with
iSHELL on the NASA Infrared Telescope Facility
Sean D. Brittain,1 John S. Carr,2 and Joan R. Najita30v1 [astro-ph.SR] 7 May 2018

1

Department of Physics & Astronomy, 118 Kinard Laboratory, Clemson University, Clemson, SC 29634-0978, USA
2
Naval Research Laboratory, Code 7211, Washington, DC 20375, USA
3
National Optical Astronomy Observatory, 950 N. Cherry Ave., Tucson, AZ 85719, USA

ABSTRACT
We present analysis of commissioning M band data acquired with the infrared echelle
spectrograph (iSHELL) on NASA’s Infrared Telescope Facility. In this paper we describe the delivered performance of the instrument for these M band observations andthe data reduction process. The feasibility of using iSHELL for spectro-astrometry
is tested on the Herbig Ae/Be star HD 179218 and we show that sub-milliarcsecond
fidelity is achievable.
1. INTRODUCTION
used to study phenomena such as binaries (Baiet al. 2004; Porter et al. 2004),
High-resolution
observations of H leyD1998; Baines
S spectroscopic
1
A M
D
outflows(Whelan&
Garcia2008; Davies et al.
CO in /2disks
1 around/ / young stars have
E been8 usedBLN
792010), and disks (e.g. Acke & van den Ancker
to elucidate the evolutionary status of warm gas
2006; Brittain et al. 2009; Pontoppidan et al.
in disks around young stars (Najita et al. 2000,
2011). While the spatial resolution of a PSF is
2003, 2007; Carr et al. 2001; Carr 2007; Britlimited to ⇠1.2D/ , the relative centroid of theMin-Kai Lin†

Dusty disc-planet interaction with dust-free simulations

strophysics, Academia Sinica, Taipei 10617, Taiwan

Jhih-Wei Chen? , Min-Kai Lin†
Institute of Astronomy and Astrophysics, Academia Sinica, Taipei 10617, Taiwan

ABSTRACT

arXiv:1805.00940v1 [astro-ph.EP] 2 May 2018

4 May 2018

ABSTRACT

Protoplanets may be born into dust-rich environments if planetesimals formed through,Protoplanets may be born into dust-rich environments
iforplanetesimals
formedstreaming
gravitational instabilities,
or if thethroughprotoplanetary disc is undergoing massloss due to disc windsdiscor photoevaporation.
Motivatedby this possibility, we explore
streaming or gravitational instabilities, or if the protoplanetaryis undergoing
mass
1 0
1
the interaction between low mass planets and dusty protoplanetary discs with focus
on disc-planet
We implement Linwe& Youdin’s
newly developed, purely hydroloss due to disc winds or photoevaporation. Motivatedbytorques.
this possibility,
exploreddynamic model of dusty gas into the Pluto code to simulate dusty protoplanetary
the interaction between low mass planets and dusty
protoplanetary
discs
with
focus
discs with an embedded planet. We find that for imperfectly coupled=dust and highmetallicity,e.g. Stokes
number 10 3purely
and dust-to-gas
ratio ⌃d /⌃g = 0.5, a ‘bubble’
on disc-planet torques. We implement Lin & Youdin’s
newly
developed,hydrodevelops inside the planet’s co-orbital region, which introduces unsteadiness
0in the0.
dynamic model of dusty gas into the Pluto code
dusty
protoplanetaryflow. toThe simulate
resulting disc-planet
torquessustain large amplitude oscillations that perwell beyond that in simulations with perfectly coupled dust or low dust-loading,/,
discs with an embedded planet. We find that forsists
imperfectly
coupled dust and highwhere co-rotation torques are always damped. We show that the desaturation of the
co-rotation
torques⌃
byd finite-sized
related to potential vorticity
metallicity, e.g. Stokes number 10 3 and dust-to-gas
ratio/⌃g = particles
0.5, ais ‘bubble’
1generation,tg5from the misalignment of dust and gas densities. We briefly discuss possible implicadevelops inside the planet’s co-orbital region, which
unsteadinessin thediscs. We also demonstratetions for introduces
the orbital evolutionof protoplanets in dust-rich
1
Lin & amplitude
Youdin’s dust-freeoscillations
framework reproduces
previous
results pertaining to dusty
flow. The resulting disc-planet torques sustain largethat
perprotoplanetary discs, including dust-trapping by pressure bumps, dust settling,
0 andsists well beyond that in simulations with perfectly
coupleddust or low dust-loading,the streaming
instability.
5
where co-rotation torques are always damped. We
theaccretion
desaturationof themethods: numerical, proto- S
Keyshowwords: that
accretion,
discs, hydrodynamics,
planetary discs
1
co-rotation torques by finite-sized particles is related
to potential vorticity generationfrom the misalignment of dust and gas densities. We briefly discuss possible implica5 3
5tions for the orbital evolution 1of INTRODUCTION
protoplanets in dust-rich discs. We andalso
demonstrate
non-isothermal discs (e.g. Paardekooper & Mellema
2006, 2008; Baruteau& Masset 2008a; Paardekooper et al.
Lin & Youdin’s dust-free framework
reproduces previous results pertaining
to dusty
The gravitational interaction between protoplanets and2010; Masset & Casoli 2010; Benı́tez-Llambay et al. 2015),
theirdust-trapping
protoplanetary disc, whichto the planet’sbumps,
orbitalprotoplanetary discs, including
byleadspressure
dust
andto name settling,a few. While thesestudies present important genevolution, likely plays a key role in shaping the architecture
eralizations,
they
have
been
limitedto purely gaseous discs.
the streaming instability.
of planetary systems (Baruteau et al. 2014, 2016). It is thus
necessary to understand how realistic disc conditions a↵ect
planet-disc interaction.
Since the pioneering study of Goldreich & Tremaine(1980) almost four decades ago, the disc-planet problem
has been extended to include many physical e↵ects expectedin protoplanetary discs. These include turbulence (e.g. Nel-

However, protoplanetary discs are dusty (Testi et al.
Key words: accretion, accretion discs, hydrodynamics, methods: 2014).
numerical,
protoIt is thus natural
to consider dusty disc-planet interaction(e.g.
Paardekooper& Mellema 2004; Fouchet et al.
planetary discs
2007; Zhu et al. 2012; Ayli↵e et al. 2012; Dipierro et al.
2016; Dipierro & Laibe 2017). Recent e↵orts in this direc-

6

IRDC G331.372-00.116

Contr

5

Figure 3. Dust continuum emission at 1.1 mm toward
ALMA1. Overlaid in contours is shown the 40% to 90%of the dust continuum emission. The red contour shows thearea of the leaf defined by the dendrogram. The dashed red
ellipse shows the area representing the first and second moments of the structure determined by the dendrogram. The
black ellipse shows the 2-D Gaussian fit obtained with CASA.
The beam is shown in the lower left corner of the image.

a self-absorbed profile at the systemic vlsr (-87.7 kms 1 ) of the core, which is determined by the central velocity of the deuterated molecules (N2 D+ and DCO+ ).
The HCO+ spectra show a blue-red asymmetry withthe blue-shifted peak brighter than the red-shifted peak.
This profile is typically explained as a sign of infall, as-rXiv:1805.01802v1 [astro-ph.GA] 4 May 2018

depends on the density profile of the core as func
INFALL SIGNATURES IN A PRESTELLAR CORE EMBEDDED IN THE HIGH-MASSµM DARKIRDC ⇢(r) / r n (MacLaren et al.
the70radial
distance,
G331.372-00.116
Here we adopt a value of n = 1.8, which has been
to be representative for high-mass star-forming
1
2
3
2, 4
Yanett Contreras, Patricio Sanhueza, James M. Jackson, Andrés E. Guzmán,
Steven Longmore,5(Mueller
et al. 2002; Garay et al. 2007). The viria
4672
Guido Garay, Qizhou Zhang, Quang Nguyπn-Lu’o’ng, Ken’ichi Tatematsu, Fumitaka Nakamura,2ofRathborne,
ALMA1 13is andderived to be Mvir = 2.4 ± 0.6 M ,Takeshi Sakai,8 Satoshi Ohashi,9 Tie Liu,10, 11 Masao Saito,2 Laura Gomez,12 Jill
14
Scott Whitakervirial parameter is ↵vir = 0.14 ± 0.08, assuming
uncertainty
in the mass value. The low value+
18
Figure 4. Left:ØHCO
(3-2) (black)aand CSO (2-1)(red)
2ntospectra overlaid to the dust c
1 Leiden Observatory, Leiden University, PO Box 9513, NL-2300 RA Leiden, the Netherlands++
virialparameterforsuggeststhatturbu
ALMA1. Right upper panel: Mean spectra across ALMA1ALMA1of the HCO(3-2),DCO
2 National Astronomical Observatory of Japan, National Institutes of NaturalØSciences,
19O
9 Mitaka,
VTokyo 181-8588,
S the stability of ALMA1(
2-21-1 Osawa,Japan
insuﬃcienttomaintainemission.
Here both optically thin tracers shows a single peak at the position of the vLSR
3 School of Mathematical and Physical Sciences, Universityof Newcastle, University Drive, Callaghan NSW 2308, Australia
Ø 1515, Las Condes,
f Santiago,
e+ shows
S etclearly
4 Departamento de Astronomía, Universidad de Chile,et Chile
al.
2011;
Tan
al. 2013;
Lu et al.
2015; Zhan
shows
red-peaked
profile,while
HCO
the typicalblue-peakedinCaminoael small
Observatorio
5 Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow
Hill, lines
Liverpool
UK
Ø 481
d
tmy
spectra of the samefour
asL3in5RF,
the
upper
panel.
the r
infallprofileetis al.
also2017).
eviden
2015;
Ohashiet Hereal. 2016;
Sanhueza
6 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
HNC there is no evidence
of infall.
It is possible
2 V
v thats magnetic )fields
5 play a role
7 The Canadian Institute for Theoretical Astrophysics (CITA), University ofØ
Toronto, 60 St. George Street, Toronto, Ontario, M5S 3H8,
1stability of this core (Zhang et al. 2014; Frau et al
Canadais then 1.19 ( thØ H2 /= 0.22 km), indicating
7 sK G/) 7 H thatK Gthe/
) where B is the magn
8 The University of Electro-Communications, Chofu, Tokyo 182-8585, JapanThe virial mass taking into theaccount
gas in the core is transonic.
core themasscontribu
density
9 RIKEN, 2-1, Hirosawa, Wako-shi, Saitama 351-0198, Japan
Ø ‒
ia
D3
10 Korea Astronomy and Space Science Institute, 776 Daedeokdaero,
aofmagnetic
field support wouldInbe
given
The virial
mass of
ALMA1
is calculated
using
order
toby:
reach v
Yuseong-gu,
Daejeon34055, RepublicKorea
11 East Asian Observatory, 660 N. A’ohoku Place, Hilo, HI 96720, USA✓✓ magnetic◆fiel✓◆ 21), ◆the12 Joint ALMA Observatory, Alonso de Córdova 3107, Vitacura, Santiago, Chile
R
5
2n
1 2
5 2n
R
v
to be of v2the+ order, MB,vir = 3(2)Mvir = 3
13 CSIRO Astronomy and Space Science, P.O. Box 76, Epping NSW 1710, Australia
A ,of
G
3
n
6
3
n
G
14 Physics Department, Boston University, Boston, MA, USA
certainty in the core’
neticand
field
have
b
where
n=
1.8notas inwhere R is the eﬀective radius of
the core,
G isAlfven
the velocity,
A is theSubmitted to ApJ
fieldbystrengths
2. TheAlfvenvelocity Suchis given
gravitational
constant, and n is a tion
constant
whose
value
A = B/
lar cores (Zhang et adepends
on the density profile of the core as function of
ABSTRACTnward prestellar core cthearadial/ K)
r 3.6-70(MacLaren
et al.
1988).
Using Galactic Plane surveys, we have selectedmassive distance,(1200 M ), ⇢(r)cold (14µm dark IRDC
G331.37200.116. This IRDC has the potential to formhigh-mass
stars aand,given
absenceof current
formation(Beuther et al. 2018)
Here
we adopt
value
ofthe
n=
1.8, which
hasstarbeen
foundsignatures, it seems to represent the earliest stages of high-mass star formation. We have mapped the whole IRDC withto be representative for high-mass star-forming regions
the Atacama Large Millimeter/submillimeter Array (ALMA) at 1.1 and 1.3 mm in dust continuum and line emission.
5.1.2. A Relatively M(Muelleret IRDC.
al. 2002;
Garay2007).
The virialmass
The dust continuum reveals 22 cores distributed
across the
In thiswork, etwe al.
analyze
the physicalpropertiesof the most massive core, ALMA1, which hasof
noALMA1
molecular outflows
detectedin theCO=(2-1),(5-4),
H2 CO
is derived
to be
Mvir
2.4SiO
± 0.6
M and
, and
its
(3-2) lines. This core is relatively massive (M = 17.6 M ), subvirialized (virial parameter ↵vir = Mvir /M = 0.14),
virial parameter is ↵vir =0.14 ± 0.08, assuming a 50%
We estimated the cand is barely aﬀected by turbulence (transonic Mach number of 1.2). Using
the HCO+ (3-2) line, we find the first
uncertainty
masswith
value.
The lowvalueof the(3-2) molecular line e
detection of infall signatures in a relatively massive,
prestellar incorethe(ALMA1)the potential
to forma high-massophysik, Karl-Schwarzschild-Str. 1, 85748 Garching, Germany
onomie, Königstuhl 17, 69117 Heidelberg, Germany, TN9 1SP, UK
Ionised gas kinematics in bipolar H II regions
Planetary Science, University of Kent, Canterbury, CT2 7NH, UK

Hannah S. Dalgleish1? , Steven N. Longmore1 , Thomas Peters2 ,Jonathan
D. Henshaw1,3 , Joshua L. Veitch-Michaelis4 , and James S. Urquhart5
1

Y; in original form ZZZAstrophysics Research Institute, Liverpool John Moores University, Liverpool, L3 5RF, UK

2 Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85748 Garching, Germany
3 Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany

ABSTRACT

arXiv:1805.00479v1 [astro-ph.SR] 1 May 2018

4 I3D Robotics Ltd, Tonbridge, TN9 1SP, UK

5 Centre for Astrophysics and Planetary Science, University of Kent, Canterbury, CT2 7NH, UK

3
I
Stellar feedback plays a fundamentalrole
in YYY;shaping
evolution of galaxies. HereAccepted XXX.
Received
in originalthe
form ZZZ
84 2c
we explore the use of ionised gas kinematics in young, bipolar H ii regions as a probe
G H
ABSTRACTof early feedback in these star-forming environments.
We have undertaken a multiStellar feedback plays a fundamental role in shaping the evolution of galaxies. Herem as a probe2/
wavelength study of a young, bipolar H ii region in
the Galactic
disc,
we explore
the use of ionised
gas G316.81–0.06,
kinematics in young, bipolar H ii regions
3
of
early
feedbackinthesestar-forming
environments.
We
have
undertakenamultiwhich lies at the centre of a massive (⇠ 10 M ) wavelength
infrared-darkcloud filament. It is-. 0 /
6
study of a young, bipolar H ii region in the Galactic disc, G316.81–0.06,
3
the centre gasof a massive(⇠ 10perpenM ) infrared-dark cloud filament.
isstill accreting molecular gas as well as driving a ⇠ which
0.2 lies
pc ationised
outflow
2 Itp84
1still accreting molecular gas as well as driving a ⇠ 0.2 pc ionised gas outflow perpendicular to the filament. Intriguingly, we observe a large
velocity
gradient(47.81±
3.21
dicular to the filament. Intriguingly, we observe a large velocity gradient (47.81 ± 3.21
2k c
1
1km s 1 pc 1 ) across the toionisedgasoutflow.
in a directionThis
perpendicular to the outflow. This
km s pc ) across the ionised gas in a direction perpendicularthekinematic signature of the ionised gas shows a reasonable correspondence with the8skinematic signature of the ionised gas shows a reasonable
correspondencewiththe comparison between our obsimulations of young
H ii regions. Based ona qualitative
servations and these simulations, we put forward a possible explanation
for the velocity
4 2
simulations of young H ii regions. Based on a qualitative
comparison between our obgradients observed in G316.81–0.06. If the velocity gradient perpendicular to the outflow is causedexplanation
by rotation of the forionisedgas,velocity
then we infer that this rotation is a direct
servations and these simulations, we put forward a possible
theresult of the initial net angular momentum in the natal molecular cloud. If this explagradients observed in G316.81–0.06. If the velocity nation
gradient
perpendicular
to should
the beoutis correct,
this kinematic signaturecommon in other young (bipolar)Hiiregions.
Wesuggestthat
furtherquantitative
analysis
flow is caused by rotation of the ionised gas, then we
infer that this rotation is a direct of the ionised gas kinematics of young H ii regions, combined with additional simulations, should improve ourunderstandingof feedback
at these If
earlystages.
result of the initial net angular momentum in the natal
molecular
cloud.
this
explawords: ISM:
ii regions;young
kinematics
and dynamics - stars: massive; protostars
nation is correct, this kinematic signature should beKey
commoninHother(bipolar)
H ii regions. We suggest that further quantitative analysis of the ionised gas kinematics of young H ii regions, combined with additional simulations, should improve our
1 INTRODUCTION
photoionising radiation, and supernovae); and thermal feedunderstanding of feedback at theseearly stages.
back (e.g. non-ionising radiation).
Feedback from high-mass stars (i.e. OB stars with M? 8
M ) is fundamental to the shaping of the visible Universe.
From the moment star formation begins, stellar feedback
commences, injecting energy and momentum into the natal
environment. This feedback can both hinder and facilitate

Key words: ISM: H ii regions; kinematics and dynamics - stars: massive;
protostars
Stellar feedback encompasses many astrophysical processes, moderating star formation from stellar scales (⌧ 1pc) to cosmological kpc-scales (e.g. driving Galactic out-

CLOUD-CLOUD COLLISION INDUCED STAR FORMATION IN IRAS 18223-1243
L. K. Dewangan1 , D. K. Ojha2 , I. Zinchenko3 , and T. Baug4

ABSTRACTIn the direction of l = 17 .6 – 19 , the star-forming sites Sh 2-53 and IRAS 18223-1243 are prominently observed, and seem to be physically detached from each other. Sh 2-53 has been investigated at
the junction of the molecular filaments, while a larger-scale environment of IRAS 18223-1243 remains
unexplored. The goal of this paper is to investigate the star formation processes in the IRAS site (area⇠0 .4 ⇥ 0 .4). Based on the GRS 13 CO line data, two molecular clouds, peaking at velocities of 45
and 51 km s 1 , are found. In the position-velocity plots, a relatively weak 13 CO emission is detected
at intermediate velocities (i.e. 47.5–49.5 km s 1 ) between these two clouds, illustrating a link between
two parallel elongated velocity structures.st.7(e)-6onto be physpe009.962686.s de0.4(l)-(u)-0.6(s).4(l)-(a)-277(.3(om)-269..4(l)-)-27ØØ

805.12141v1 [astro-ph.SR] 30 May 2018

The Eccentric Cavity, Triple Rings, Two-Armed Spirals, andDouble Clumps of the MWC 758 Disk
Ruobing Dong1,2 , Sheng-yuan Liu2 , Josh Eisner1 , –SeanAndrews3 , Je↵rey Fung4 , Zhaohuan
29 –Zhu5 , Eugene Chiang4 , Jun Hashimoto6 , Hauyu Baobab Liu7 , Simon Casassus8 , Thomas
Deprojected 0.87 mm Continuum Emission Map
Esposito4 , Yasuhiro Hasegawa9 , Takayuki Muto10 , Yaroslav Pavlyuchenkov11 , David
Wilner3 , Eiji Akiyama12 , Motohide Tamura5,13 , and John Wisniewski14

g
c
” l b
4- . )
RM 6 MB 2, LC
JJ CJotus <7
r Wu

Ø 2

2 4RCIjAP
g/ AP

ABSTRACT

<7
pstW

m l
b (

Spatially resolved structures in protoplanetary disks hint at unseen planets.
Previous imaging observations of the transitional disk around MWC 758 revealed.- JJ ) )/ JAN , . , ( AP ( T8R%B AJ
an inner cavity, a ring-like outer disk, emission clumps, and spiral arms, all possibly generated by companions. We present ALMA dust continuum observationsof MWC 758 at 0.87 millimeter (mm) wavelength with 43⇥39 mas angular resØolution (6.9⇥6.2 AU) and 20 µJy beam 1 rms. The central sub-mm emission

0, T8R
Ø
g
c l
A1 )(
1
=21/
Ø ==5bga ( )( APe1

Steward Observatory, University of Arizona, AZ 85721, USA

2

Institute of Astronomy and Astrophysics, Academia Sinica, Taipei 10617, Taiwan

3

Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138,Ø
USA
y

d

8PL

e

4

Department of Astronomy, University of California at Berkeley, Campbell Hall, Berkeley, CAØ 94720-3411,
<7
USA

Ø (

otus

2.— Deprojected image of MWC 758 assuming i=21 and PA=62 in Cartesian and polar (radialDepartment of Physics andFig.
Astronomy,
University of Nevada, Las Vegas, 4505 South Maryland Parkway,Ø
31 , . 9
Las Vegas, NV 89154, USA

5

6

Astrobiology Center of NINS, 2-21-1, Osawa, Mitaka, Tokyo 181-8588, Japan

x
DM%M0
x
-9

805.12141v1 [astro-ph.SR] 30 May 2018

32 –The Eccentric Cavity, Triple Rings, Two-Armed Spirals, andDouble Clumps of the MWC 758 Disk
Ruobing Dong1,2 , Sheng-yuan Liu2 , Josh Eisner1 , Sean Andrews3 , Je↵rey Fung4 , Zhaohuan
Zhu5 , Eugene Chiang4 , Jun Hashimoto6 , Hauyu Baobab Liu7 , Simon Casassus8 , Thomas
Esposito4 , Yasuhiro Hasegawa9 , Takayuki Muto10 , Yaroslav Pavlyuchenkov11 , David
Wilner3 , Eiji Akiyama12 , Motohide Tamura5,13 , and John Wisniewski14

P

ABSTRACTØ nti y mn ( +aʼaSpatially resolved
protoplanetary
Ø structures.23. in406
L disks
P hint at
Lunseen planets.
Previous imaging observationstransitionalM
disk LaroundØ . < of the.23.
aMWC 758 revealed
an inner cavity, a ring-like outer disk,Nemission
N clumps, and spiral arms, all posM
sibly generated by companions. We present ALMA dust continuum observations
Øa) n Iy iàof MWC 758 at 0.87 millimeter (mm) wavelength with 43⇥39 mas angular resb rxu 1
L– 33 –

olution (6.9⇥6.2 AU) and 20 µJy beam
1

<<on
LN
A,

rms. The central sub-mm emission

Steward Observatory, University of Arizona, AZ 85721, USA

2

Institute of Astronomy and Astrophysics, Academia Sinica, Taipei 10617, Taiwan
Ø31
g3
Harvard-Smithsonian Center for
Astrophysics, 60 Garden Street,
Cambridge,
406
5.-+
J -MA 02138,
J USA=
Department of Astronomy,ØUniversityof California at Berkeley,94720-3411,<<<aon
p Campbell Hall,gBerkeley, CARga
USA
4

Ø

a

5

1D

Department of Physics and Astronomy, University of Nevada, Las Vegas, 4505 South Maryland Parkway,
Las Vegas, NV 89154, USA
6

Astrobiology Center of NINS, 2-21-1, Osawa, Mitaka, Tokyo 181-8588, Japan

IoI

p
SL

aris, PSL, CNRS, UPMC, Université Paris Diderot, 5 place Jules Janssen, 92195 Meudon, Franced Astronomy, University of Sheffield, Hounsfield Road, Sheffield S3 7RH, UK

Is stellar multiplicity universal? Tight stellar binaries in
the Orion Nebula Cluster
Gaspard Duchêne,1,2? † S. Lacour3 , E. Moraux2 , S. Goodwin4 , J. Bouvier2

YY; in original form ZZZ

1 Astronomy Department, University of California Berkeley, CA 94720, USA
2 Université Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France

3 LESIA/Observatoire de Paris, PSL, CNRS, UPMC, Université Paris Diderot, 5 place Jules Janssen, 92195 Meudon, France

ABSTRACT

arXiv:1805.00965v1 [astro-ph.SR] 2 May 2018

4 Department of Physics and Astronomy, University of Sheffield, Hounsfield Road, Sheffield S3 7RH, UK%. n
We present a survey for the tightest visual binaries among 0.3–2 M members the
XXX. Received YYY; in original form ZZZ
1%Orion Nebula Cluster (ONC).AcceptedAmong
42 targets, we discovered 13 new 0.00025–0.0015
61
companions. Accounting for the Branch bias, we find a companion star fraction (CSF)
ABSTRACT+8in the 10–60 au range of 21 5 %, consistent withWethat
observed
star-forming
0upresent
a survey for in
the other
tightest visualbinaries among 0.3–2 M members theOrion Nebula Cluster (ONC). Among 42 targets, we discovered 13 new 0.00025–0.0015
regions (SFRs) and twice as high as among fieldstars;Accounting
this excess
is foundwitha3
N
companions.
for the Branchbias, we finda companion
star fraction (CSF)+8
in the 10–60 auof 21 5 %, consistent
with thatthis
observed in other star-forming
high level of confidence. Since our sample is dominatedbyrangedisk-bearing
targets,61
60
regions (SFRs) and twice as high as among field stars; this excess is found with aindicates that disk disruption by close binaries is inefficient,
or
has
not
yet
taken
place,
high level of confidence. Since our sample is dominated by disk-bearing targets, thisC6 61
indicatesthat disk
disruption
by closebinaries isoutside
inefficient, or has not yet 4
taken place,in the ONC. The resulting separation distribution
in theONC
drops
sharplyin the ONC. The resulting separation distribution in the ONC drops sharply outside
O1
60 au. These findings are consistent with a scenario
in whichtheinitial
60 au. Thesefindings are
consistent
withmultiplicity
a scenario in which the initial multiplicity
properties, set by the star formation process itself, are identical in the ONC andproperties, set by the star formation process itself,
are identical in the ONC and2
in other SFRs and subsequently altered by the cluster’s dynamical evolution. Thisthat the dynamicalfragmentation process
does not dependon the global properties of ain other SFRs and subsequently altered by theimplies
cluster’s
evolution.
Thisslatter areOmolecular cloud, but on the local properties of prestellar cores, and that the
implies that the fragmentation process does not self-regulated
depend ontheglobalpropertiesofato be nearly identical in a wide range of environments.
These results,
O1
N
however,
raise
anew
the
questionoftheorigin
of
field
stars
as
the
tight
binaries wemolecular cloud, but on the local properties of prestellar
cores,
andthat
thelatterarehave discovered will not be destroyed as the ONC dissolves into the galactic field. O1
O3
self-regulated to be nearly identical in a wide range
of environments.
It thus appears
that most field starsThese
formed inresults,
regions that di↵er from well-studied
SFRs in the Solar neighborhood, possibly due to changes in core fragmentation on
M Ouhowever, raise anew the question of the origin ofstars as the tight binaries we
Gyrfield
timescales.
ahave discovered will not be destroyed as the ONC
dissolves
field.– open cluster and associaKey words:
binaries:intovisual –thestars:galactic
pre-main-sequence
individual:
Orion
Nebulafrom
Cluster well-studied
It thus appears that most field stars formed in tions:regions
that
di↵er
O1
SFRs in the Solar neighborhood, possibly due to changes in core fragmentation on
Gyr timescales.
1

INTRODUCTION

cus has been on the hunt for significant di↵erences between
the multiplicity properties of di↵erent stellar populations.
From the earliest studies of populations of T Tauri stars, it
was clear that visual binaries are twice as common in nearby
SFRs as they are among field stars of similar masses at sepa-

stellar multiplicity in the youngest
stellar cluster and associaKey words: binaries: visualThe– ubiquity
stars:ofpre-main-sequence– openpopulations has been long established, proving that thistions: individual: Orion Nebula
Cluster
is aninherent feature of the star formation process itself

DEEP, HIGH-RESOLUTION ALMA OBSERVATIONS
1
3
4
1
J. A. Eisner1 , PROTOPLANETARY
H. G. Arce2 , N. P.
Ballering, J.INBally, S. M.
Andrews, R. INITIAL
D. Boyden, J. FROMDi Francesco5 , M.
DISKPROPERTIESTHE ORIONNEBULA
CLUSTER:RESULTS5
Fang1 , D. Johnstone5 , J. S. Kim1 , DEEP,R. K.HIGH-RESOLUTION
Mann5 , B. Matthews, I. Pascucci6 , L. Ricci7 , P. D. Sheehan8 , J. P.
ALMA OBSERVATIONS
9Williams
1
2
1
3
J. A. Eisner , H. G. Arce , N. P. Ballering , J. Bally , S. M. Andrews4 , R. D. Boyden1 , J. Di Francesco5 , M.

Fang1 , D. Johnstone5 , J. S. Kim1 , R.Accepted
K. Mann5 for, B. Publication
Matthews5 , I.
inPascucci
ApJ 6 , L. Ricci7 , P. D. Sheehan8 , J. P.
9Williams
Accepted for Publication in ApJ

3669v1 [astro-ph.SR] 9 May 2018

ABSTRACTABSTRACTof the Orion Nebula Cluster that provide the
We present ALMA 850 µm continuum observations
Weresolution
present ALMA
8500.00µm
continuum
observations of the Orion Nebula Cluster that provide thehighest angular(⇠
1⇡00 40 AU) and deepest sensitivity (⇠ 0.1 mJy) of the region tohighest angular resolution (⇠ 0. 1 ⇡ 40 AU) and deepest sensitivity (⇠ 0.1 mJy) of the region todate. We mosaickeda field containing⇠ 225
ornear-IR-identified
near-IR-identified
young⇠ 60 of whichdate. We mosaickeda field containing⇠ 225optical
optical or
young stars,⇠ 60stars,of which
are also optically-identified“proplyds”.
detect continuum
emission
at 850 µm
towards
80%
are also optically-identified“proplyds”.
WeWedetect
continuum
emission
at 850µm⇠ towards⇠ 80%of the proplyd sample, and ⇠ 50% of the larger sample of previously-identified cluster members.
Detected objects have fluxes of ⇠ 0.5–80 mJy. We remove sub-mm flux due to free-free emission insome objects, leaving a sample of sources detected in dust emission. Under standard assumptions ofisothermal, optically thin disks, sub-mm fluxes correspond to dust masses of ⇠ 0.5 to 80 Earth masses.
We measure the distribution of disk sizes, and find that disks in this region are particularly compact.
Such compact disks are likely to be significantly optically thick. The distributions of sub-mm fluxand inferred disk size indicate smaller, lower-flux disks than in lower-density star-forming regions ofsimilar age. Measured disk flux is correlated weakly with stellar mass, contrary to studies in other star
forming regions that found steeper correlations. We find a correlation between disk flux and distancefrom the massive star ✓1 Ori C, suggesting that disk properties in this region are influenced strongly
by the rich cluster environment.
Subject headings: Galaxy:Open Clusters and Associations:Individual: Orion, Stars:Planetary Systems:Protoplanetary Disks, Stars: Pre-Main-Sequence
1. INTRODUCTION

Protoplanetary disks are the birth-sites of planetarysystems, and the properties of disks relate directly tothe planets that may potentially form. In particular,
disk mass constrains the mass budget for planet formation, and hence the mass distribution of planets. The
minimum-mass solar nebula (MMSN) needed to form thecore of Jupiter likely formed on a much shorter timescale,< 1 Myr (Kruijer et al. 2017; Desch et al. 2017). Protoplanetary disks with cleared gaps or holes around stars
aged . 1 Myr also suggest rapid formation of giant planets (e.g., ALMA Partnership et al. 2015; Dong et al. 2015;
Sheehan & Eisner 2017). Higher disk masses accelerate
planet formation timescales (since collision rate scaleswith surface density). The apparently rapid growth of

1, 2

1

1, 2

1

3

4

5

1

R. Fedriani , A. Caratti o Garatti , D. Co↵ey , R. Garcia Lopez , S. Kraus , G. Weigelt , B. Stecklum , T.P. Ray ,Received 27 October 2017 / Accepted
23 May 2018
and C. M. Walmsley,??
1Dublin Institute for Advanced Studies, School of Cosmic Physics, Astronomy & Astrophysics Section, 31 Fitzwilliam Place, Dublin
2, Irelande-mail: fedriani@cp.dias.ie
2
University College Dublin, School of Physics, Belfield, Dublin 4, Ireland
3
School of Physics, Astrophysics Group, University of Exeter, Stocker Road, Exeter EX4 4WL, UK
4
Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany
5
Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany

ABSTRACT

Xiv:1805.11512v1 [astro-ph.SR] 29 May 2018

11512v1 [astro-ph.SR] 29 May 201

University College Dublin, School of Physics, Belfield, Dublin 4, Ireland
School of Physics, Astrophysics Group, University of Exeter, Stocker Road, Exeter EX4 4WL, UK
4
Parsec-scale
byD-53121
high-massstellar objects.
Max-Planck-Institut für Radioastronomie,
Aufjets
demdriven
Hügel 69,
Bonn,young
Germany
5
Thüringer Landessternwarte Tautenburg,
Sternwarte
07778
Connecting
the au-5,and
the Tautenburg,
parsec-scaleGermany
jet in IRAS 13481-6124?
3

Context. Protostellar jets in high-mass young stellar objects (HMYSOs) play a key role in the understanding of star formation andprovide us with an excellent tool to study fundamental properties of HMYSOs.
Received 27 October/ Accepted 23 May
2018
Aims. We aim at studying the physicaland2017kinematic
propertiesof the near-IR (NIR) jet of IRAS 13481-6124 from au to parsec
scales.
ABSTRACT
Methods. Our study includes NIR
data
from
the
Very
Large
Telescope
instruments SINFONI, CRIRES, and ISAAC. Information
Context. Protostellar jets in high-mass young stellar objects (HMYSOs) play a key role in the understanding of star formation andprovideenvironment
us with an excellent tool
study fundamental
properties
of HMYSOs. The technique of spectro-astrometry is performed with
about the source and its immediate
istoretrieved
with
SINFONI.
Aims. We aim at studying the physical and kinematic properties of the near-IR (NIR) jet of IRAS 13481-6124 from au to parsec
CRIRES to study the jet on au scales.
The parsec-scale jet and its kinematic and dynamic properties are investigated using ISAAC.
scales.
Methods. Our study includes NIR data from the Very Large Telescope instruments SINFONI, CRIRES, and ISAAC. Information
Results. The SINFONI spectraabout
in thethesource
H andandK bandare richin emission
lines
thatof spectro-astrometry
are mainly isassociatedits immediate
environmentis retrieved
with SINFONI. The
techniqueperformed with with ejection and accreCRIRES to study the jet on au scales. The parsec-scale jet and its kinematic and dynamic properties are investigated using ISAAC.
tion processes. Spectro-astrometry
is applied to the Br line, and for the first time, to the Br↵ line, revealing their jet origin with
Results. The SINFONI spectra in the H and K band are rich in emission lines that are mainly associated with ejection and accretion displacements
processes. Spectro-astrometry
the BrThisline, andfor the first
the Br↵ line, revealing
jet origin with of the au-scale jet and to
milliarcsecond-scale photocentre(11is applied
15 toau).
allowsustime,toto constrain
the their
kinematics
milliarcsecond-scale photocentre displacements (11 15 au). This allows us to constrain the kinematics of the au-scale jet and toits position angle(⇠ 216 ). ISAAC spectroscopy
H emission along
the parsec-scalejet, which allows us jet,to inferwhichkinederive its position angle (⇠ 216 derive). ISAAC
spectroscopy
reveals reveals
H2 emission
along
the parsec-scale
allows us to infer kinematic and dynamic properties of the NIR parsec-scale jet. The mass-loss rate inferred for the NIR jet is Ṁ
⇠ 10 M yr andmatic and dynamic properties ofjet.is roughly
The constantmass-loss
rate history
inferred
forstar.
the
NIR estimate
jet isof Ṁejec ⇠ 10 4 M yr 1 andthe thethrust isNIRṖ ⇠ 10parsec-scale
M yr km s , which
for the formationof the young
A tentative
the ionisation
fraction is derived for the massive jet by comparing the radio and NIR mass-loss rates. An ionisation fraction . 8% is
the thrust is Ṗ ⇠ 10 2 M yr 1 km
s 1 which, whichistheroughly
constant
theformation
historyof atheobtained,means thatbulk of the ejecta
is traced byfor
the NIRjet andthat the radio jet
only delineatessmall young
portion of it.star. A tentative estimate of
the ionisation fraction is derivedKeyfortheISM:massive
jet bycomparing
the radio
and NIR
mass-loss
An ionisation fraction . 8% iswords.
jets and outflows– ISM:
kinematics and dynamics– stars: pre-main
sequence– stars: massive rates.
– stars: individual:
IRAS 13481-6124 – technique: spectroscopic
obtained, which means that the bulk of the ejecta is traced by the NIR jet and that the radio jet only delineates a small portion of it.
2

2

1

ejec

1

4

1

/631 ISM:
2 3jets and outflows
R0
2 kinematics
a and5dynamics
4R tions
HY
8sequenceOT – stars: individual:c
Key words.
– ISM:–uO
stars:
pre-main–throughstars:
massive
1. Introductionof HMYSO
discs in Keplerianrotatione
modellingof CO band-head emission (Ilee et al. 2013), iii) direct detecIRAS– technique:spectroscopic
O13481-6124
p
a in Rn
Injs
recentyears, significant progressO
has been madeun- tion ofI
HMYSO discs in molecular tracers (BeltránYH& de Wit MN
derstanding the formation of high-mass young stellar objects 2016), iv) detection of several parsec-scale collimated infraredeS O/ 8A B (HMYSOs)/ (i.e. M⇤ K8 M , LSr
po Garatti
Set al. V02 Varricattaet al. 2010;Oy
5 ⇥ 103 L ). The latest jets (Carattibol2008, 2015a;
observational and theoretical studies present evidence that tips Cesaroni et al. 2013), and v) discovery of the first disc-mediatedLthe balance of favour in a key debate over how high-mass stars accretion burst in a 20 M YSO (Caratti o Garatti et al. 2017).

1. Introduction

8aSIf, as now
likely, HMYSOs
the accretiontionsof appears
HMYSO
discsform
inthroughKeplerianrotation through modelling
ejection process, then studies of the jet and outflow have the po-form. It now seems likely that HMYSOs are born in the same
way as their low-mass counterparts, via disc accretion, rather

And then compute the tensor’s eigenvalues. The numberSELF-GRAVITY,of positive eigenvalues
E encodes information about
ARE ELIAS 2-27’S SPIRAL ARMS DRIVEN BY
OR BY A COMPANION?
2.1. Hydrodynamics
thedimensionalityof the flow. For example, particles
A COMPARATIVE SPIRAL
MORPHOLOGY
STUDY
1, 2
5
DuncanH. Forgan,inJohn D.withIlee,3 E
and=Farzana
Meru3, 4,
1 indicate
theirmotion is planar, consistent
Our hydrodynamic simulations are fully
described
1 SUPA, School of Physics and Astronomy, University ofwith
motionin theundisturbed
disc. Particles with
St Andrews,
North Haugh,
St Andrews
KY16 9SS, UK
Meru et al. (2017), but for completenesswe briefly reiterparent molecular cloud (22), accretes material
2 Centre for Exoplanet Science,
University
ofwithSt aAndrew,
St Andrews, KY16 9SS, UK
from its surrounding
diskE
accretion=mass
2 indicate
2D filamentary motions (in this case, spiate
somesalient
aspects.
The
simulations
areperformed
3 Institute
rate
of
8
×
10
M
year
(25).
Previous
obof
Astronomy,
UniversityofCambridge,
Cambridge,
CB3 0HA, USA
Ø
cn l
d
g
ai
d
servations at 0.6″ to 1.1″ angularresolution were4
ral
structure).
If theCV4
spiralstructure is strong enough,
Smoothed
Particle
Departmentof Physics, HydroUniversity of Warwick, Gibbet Hill Road, Coventry,
7AL, UK
well described by a smooth and axisymmetricØusing the three-dimensional5 Centre
pnu
for Exoplanets and Habitability,
University
Warwick,
Hill theRoad, centre
Coventry, ofCV4the
7AL,arm
UK will possess E = 3
distributionof materialofin
the disk thatGibbet
extends
particles
near
dynamics
code(sphNG)
includingheating
due
to
work
near
the
stellarphotosphereanddecreasesmonoØ 2HE N ( (- 7
+ , 7 NPC
7QM tonically0H NN
55with distance fromthe star(20, 23).
(3D
done and the radiative transfer of(Received
energyJanuary
in theflux1, 2018;
RevisedJanuary
1,collapse).
2018;
Accepted January 1, 2018)
To estimate theopticaldepth oftheobserved
7 EN** 7 NPcnldust continuum emission, we
performed
We
canradi-therefore identify particles belonging to thelimited di↵usion limit (Whitehouse et al. 2005; WhiteSubmitted
toRADMC-3D
ApJ (26)
ative transfer
calculations using
1.3 mm (17), using thespiralprevious surface
den- their E value, and discard the other parusing
house & Bate 2006). A detailed description of theatsitycode
constraint found for the Elias 2-27 disk (20).
ABSTRACTThis model reproducestheazimuthally averaged
ticles.
This allows us to trace the spine of the spiralcan be found in Meru (2015) and Meru et al. (2017).
radial profile of the observed ALMA 1.3-mm conThe spiralj
waves detected in the
protostellar
disc
Elias
2-27
have beenofsuggested
as density), using
Ø my ʼWm
tinuumemission (fig. S1)(17).
Atsurroundinga radial distancestructure(i.e.
thelocationmaximum
Our reference model consists
of
a
0.5M
star,
modfromthestar(hereafterreferredtoasradiusandthe disc being gravitationally unstable. However, previous work has shown that a massive,Ø )1 = 4 NLD83evidence
7discof undergoing+ 7 NP an encounterPO )+denoted by PR) larger2thanaR friends-of-friends-like≈ 10 AU, the emisalgorithm,
whichyields a set ofForgan etal.
stablea massive
elled as a sink particle, surrounded by a discwhose
inision withis opticallythin and thuscompanion
traces the densityare also consistent with the observa7 EN(* 7 NPof solid material
down tothe midplaneof thehydrodynamic(x,y)particle
pointsfor each individual
spiral. Each arm is thenWe compare the spiral morphology
of smoothed
simulations modellingtial temperature (T ) andtions.
surfacedensity (⌃) varydisk.withAt the location of the spiral structures (from2gravitationallydiscsymmetric,
tightlyspiral arms with
R = 100 to 300AU),produces
thefitted
azimuthally
averagedØzt d7 ENboth cases.
-.The
7 NP
.7 PLjunstable
separately
via woundminimisation
to a variety of spiradius (R) as
optical
depth
t
of
the
dust
continuum
emissionconstant pitch angle, as predicted by the literature. The companion disc’s arms are asymmetric, withis t = 0.1 at R = 100 AU, ral
decreasing
to t = 0.02(assuming a constant uncertainty ofmodels= 0.1
M +P
pitch angles that increase with radius.
However,these
are not well-fitted by standard analytic
at R = 300
AU (fig. S1B),
whicharms
is consistent
0.75
with thepeakAUbrightness
temperaall points).
WeR
expressions,due
to the high disc mass
andmeasured
relatively
low forcompanion
mass. WenoteusethatNelder-Meaddi↵erences (or (amoeba) optiT (R) = 13.4 K
,
and
(2)
ture onthe spirals of 1.2 K at R = 150 AU.
200
au
2
indeed similarities) in morphology between
pairs ofare
spiralsa to
crucialdiscriminant
between scenarios
The spiral structureseven moreisevident
misationobtainsaid
minimum, implemented via
0.75hence future studies
in Fig. 2A, mustin which fit
the data
has been
projected
R2-27, and
for
Elias
spiralarms
individually.
If
Elias
2-27
continues
to⌃(R) = ⌃0 200au
into a(3)polar coordinate scipy.optimize.minimize.
grid that accounts forshow symmetric tightly wound spiralarms
in futurethen we posit that it is the firstthe viewing
geometryof the disk.observations,
In polar coordi-

1805.08041v1 [astro-ph.SR] 21 May 2018

2. METHODOLOGY

−8

⊙

−1

nates, a ring with zero eccentricity would haveexample of a gravitationallyunstabledisc.
spirals are commonly found in isolated
a constant
all polarLogarithmic
angles. However,Ø
e betweens oRinobservedcjradius forprotostellar
respectively,= 10 au andhn
Rout =l350
au.
shown in Fig. 2A are two bright structures thatand in discs driven by encounters with a comin radius from ~100GI
to 300 discs
AU as the polarstars: individual(Elias grow
2-27)
— stars:
pre-mainsequence— hydrodynamics — protoplanThe first simulation is Keywords:
a gravitationallyunstable
disc
angle
increases.
The brightestof these two
strucpanion:
lies northwest of the star, labeled “NW”;
2 disks kru— planet-disk
interactions
Ø 6with3 ⌃0 = 6a⇥ 10
c 7 M auetary(GI),, giving
a totaltures
the discspiral structure southeast of the star is labeledr = aeb✓ ,(5)“SE.” In Fig. 2B, we present the surface brightness
mass of 0.24 M , and an initial1.Toomre
parametercontrast
Q<
1.ble
Surfacedensityunstable disc (left)
andundergo
the companion encounter disc (right) overlaid with theof the NW Figure
and SE arms,
definedasthe of the gravitationally
INTRODUCTION
to non-axisymmetricperturbations,which
resultsof the tache
identification algorithm (black crosses). Individual arms are identified as either ’upper’ or ’lower’ inratio between the peakof emission
at the arm
whereisspiralcylindricalradius,and ✓ is the azimuthal answingr(17).
amplification
into spiralstructures.
1 beyond ⇠ 250 au. Spiral structures generated by gravitationallycase.
and the backgroundsurfacebrightness
Weunsta-eachfound that both arms have similar contrasts
gle.
The
a parameter
determines
theinitialdistanceofNatta et al. 2006), hostble protostellar
discs play a crucial
the evolution
In the second simulation(Companion),⌃0role=in1.96⇥
ing ofwhethera protostellar
disc theseis gravitationallyunsta1 Myr;
Luhman& Rieke 1999;
early
structures
are typicallystrongranging
between values
1.3 and At
2.5.
The
spiral times,
7

2

ble -contrast
measuring
physicalproperties
determining
ing a ClassII circumstellar disc potentially exhibiting a
armseventuallyreach their highest
at R = its150
AU,of protostars and the planetary systems they
globalmodes,
which
can andachieve
rapid accretionof theForganet al. 2-27’S SPIRAL ARMS DRIVEN BY SELF-GRAVITY, OR BY A COMPANION?
ARE ELIAS
Forgan et al.
A COMPARATIVE SPIRAL MORPHOLOGY STUDY

44The Spiral Morphol
The Spiral Morph

Duncan H. Forgan,1, 2 John D. Ilee,3 and Farzana Meru3, 4, 5
1 SUPA, School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews KY16 9SS, UK

1805.08041v1 [astro-ph.SR] 21 May 2018

2 Centre for Exoplanet Science, University of St Andrew, St Andrews, KY16 9SS, UKØ laAstronomy,Mrnp7
3 Institute of
Universityof Cambridge, Cambridge, CB3 0HA, USA
4 Department of Physics, University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL, UKØ rm gk M /5 Centre for Exoplanets and Habitability, University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL, UKØ< 7
0 .rmu g(Received
k Januaryi1, 2018; Revised January 1, 2018; Accepted January 1, 2018)
Submitted to ApJØoE
MABSTRACTh c
The spiralprotostellar discØ wavesodetected in theMla surrounding Elias 2-27 have been suggested as
evidence of the disc being gravitationally unstable. However, previous work has shown that a massive,
Ø
*20
M rm
7
stable disc undergoing an encounter with a massive companion are also consistent with the observa< morphology
o of stions. We compareE
the spiralsmoothed <particle hydrodynamic simulations modellingboth cases.ØThe gravitationally unstable disc produces symmetric, tightly wound spiral arms withconstant pitch angle, as predicted by the literature. The companion disc’s arms are asymmetric, withpitch angles that increase with radius. However, these arms are not well-fitted by standard analytic
expressions, due to the high disc mass and relatively low companion mass. We note that di↵erences (orindeed similarities) in morphology between pairs of spirals is a crucial discriminant between scenarios
6
Forgan et al.
for Elias 2-27, and hence future studies must fit spiral arms individually. If Elias 2-27 continues toTable
1. Best fitting
parameters
for both
the arms
G.I. andinCompanion
simulation for thethen
spiral wefunctionsshow
symmetric
tightlywound
spiralfuture observations,
positdescribedthat itin isSection
the 2.2.
first
In each case, ‘up’ and ‘low’ refer to the upper and lower arms identified in Figure 1, respectively.
observed example of a gravitationally unstable protostellar disc.

Gravitational Instability
Companion
PURELOG
VARLOGVARLOGN
POW
PURELOG
VARLOGVARLOGN
POW 3. As Figure 2, but for the Companion simulation. The
Figure 2. The isolated GI disc simulation, overlaidKeywords:
with the tachespine individual
points and fourdi↵erent
fitted—spiralfunctions(see sequence — hydrodynamics
Figurestars:(Elias2-27)stars:
pre-main—
protoplanUp spine
Low
UpfittedLow
Up Low
Low
Up
Low
Up
Low
Up
Lowcircle.
ext).
byFigurea redigure 2. The isolated GI disc simulation, overlaid with the tachepoints Up
and fourLowdi↵erentspiral functions(see Up
3. As Figure 2, but for the Companion simulation. T
etary56.9
disks— planet-disk
a
29.2
111.8
56.2
110.3interactions
56.8
55.3 11.5 64.2
33.0
39.4
73.3
46.5
38.5
8.4by a 1.9
ext).
red
circle. the results of tache’s spiral spine idenFigure 1 shows
pirals are typically found with the following function
where b = b0 at r = a, and the PURELOG solution isb00.208 0.205 0.191 0.244 0.123 0.216
0.288 0.243 0.208
0.225 0.148 0.201
tification
the GI(left)
the Companion
or b (Zhual. 2015),
recoveredc =r 0.
Weandalsothecheck
specificallywhether
Figure 1forshows
thediscresultsof andtache’sspiral spinedisc
idenpirals
are ettypically
found with the following functionwhereb = forb at= a,
PURELOGsolutionis
INTRODUCTION
ble
to non-axisymmetricperturbations, (right).
which
undergo[ ] 1.
11.75
11.59 0
17.0
14.2
Note
fordiscthe(left)
Companion
the spine
a linear dependenceof balso
withcheckr is sufficientbywhetherrunningtification
for that
the GIand the disc,Companion
disc
or b (Zhu et al. 2015), ⇣ r ⌘1+⌘ r↵recoveredfor c = 0. We
specificallyc-0.009 -0.029
0.1-0.0060.0003 into
0.00020.014structures.
0.005
pswing amplification
spiralidentificationslightly
missesthelocationofthecomfitswithn=
1(VARLOGN).
Finally,todoublecheckb(r) = hp⇣ ⌘,(7)(right).
Note
that
for
the
Companion
disc,
the
spine
a
lineardependence
of
b
with
r
is
sufficientbyrunningSpiralstructuresgeneratedbygravitationallyunstarrp 1+⌘ r↵r↵ rp↵n-0.49do indeed
0.35
1.0
0.67 1.26
2.40
1.92
1.0
1.0
1.64
1.14This is due to the fact that the particles impanion.
that
the a
a1.0logarithmic
form,
identificationslightly misses the location of the comfits
withnspirals= 1 (VARLOGN).
Finally,
to double checkb(r) = hp,(7) 2 discs
play
crucialrole
in possesstheevolutionAt
earlytimes,
thesestructuresare 9.91
typicallystrongrr↵ rp↵ble protostellar
1.98
3.98
3.63
3.22
3.02
3.26
3.96
4.13
7.80
4.52
3.54
3.85
4.29
2.39
5.03 surrounding
mediately
the companion have a di↵erent
we also fit a power spiral function (POW), where↵

panion. This is due to the fact that the particles imthat the spirals do indeed possess a logarithmic form,
where rp is the orbital radius of the companion⌦ / r ,and theof protostars
planetary systems they eventually
global modes, which can achieve rapid accretion of the