36 Unveiling the nature of candidate high-mass young stellar objects in the
Magellanic Clouds with near-IR spectroscopy

2

1 Department of Astronomy, University of Michigan, 311 West Hall, 1085 South University Avenue, Ann Arbor, MI 48109, USA
2 UK Astronomy Technology Centre, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK

3 Department of Physics & Astronomy, Johns Hopkins University, 3400 N. Charles St., Baltimore, MD 21218, USA
4 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA

Accepted 2018 November 27. Received 2018 November 27; in original form 2018 August 31

ABSTRACTAs nearby neighbours to the Milky Way, the Large and Small Magellanic Clouds (LMC and
SMC) provide a unique opportunity to study star formation in the context of their galactic
ecosystems. Thousands of young stellar objects (YSOs) have been characterized with largescale Spitzer and Herschel surveys. In this paper, we present new near-IR spectroscopy of fivehigh-mass YSOs in the LMC and one in the SMC. We detect multiple hydrogen recombinationlines, as well as He I 2.058 µm, H2 , [Fe II], and [S III] in these highly excited sources. We
estimate the internal extinction of each source and find that it is highest for sources with theyoungest evolutionary classifications. Using line ratios, we assess the dominant excitation
mechanism in the three sources where we detect both H2 2.12 µm and [Fe II] 1.64 µm. In
each case, photoexcitation dominates over shock excitation. Finally, we detect CO bandhead
absorption in one of our LMC sources. While this feature is often associated with evolvedstars, this object is likely young with strong polycyclic aromatic hydrocarbons (PAHs) andfine-structure emission lines tracing an H II region detected at longer wavelengths. Comparedto high-mass YSOs in the Galaxy, our sources have higher bolometric and line luminosities,
consistent with their selection as some of the brightest sources in the LMC and SMC.
Key words: stars: formation – stars: massive – stars: pre-main-sequence – stars: protostars.

1 I N T RO D U C T I O N
The formation and evolution of high-mass stars remains an open
question in astrophysics. The recent explosion of Galactic plane surveys has provided an unprecedented view of thousands of actively
star-forming clouds throughout the plane of the Milky Way (e.g.
Hoare et al. 2005; Urquhart et al. 2008; Schuller et al. 2009; Molinari et al. 2010; Aguirre et al. 2011). Unlike previous targeted observations, these surveys did not select for a particular star-formation
indicator, instead providing an unbiased sample. This large population of clumps has enabled construction of an evolutionary sequenceand mass function for high-mass stars (e.g. Svoboda et al. 2016).
Galaxy-wide surveys, particularly those that target galaxies external to the Milky Way, allow detailed studies of the association
between star formation and environment. Two of the closest galaxies
to the Milky Way, the Large and Small Magellanic Clouds (LMCand SMC), are particularly prime for observational scrutiny (e.g.
Whitney et al. 2008; Dobbs et al. 2010; Louie, Koda & Egusa 2013;
Sewiło et al. 2013; Choi et al. 2015; Lewis et al. 2015; Ochsendorf⋆ E-mail: megan.reiter@stfc.ac.uk

et al. 2016). The LMC and SMC provide many sources at a uniform
distance (∼50 kpc, Pietrzyński et al. 2013 and ∼60 kpc, Scowcroft
et al. 2016, respectively) in irregular galaxies with favourable orientations. Unlike other extragalactic laboratories, the LMC and SMC
are close enough to resolve individual high-mass star-forming regions. Multi-wavelength surveys particularly with Spitzer and Herschel have uncovered a wealth of candidate young stellar objects(YSOs) in both galaxies (e.g. Meixner et al. 2006; Whitney et al.
2008; Meixner et al. 2013; Sewiło et al. 2013; Seale et al. 2014).
Hundreds of candidate YSOs have been targeted for follow-up observations with the Spitzer InfraRed Spectrograph (Spitzer IRS;
Oliveira et al. 2009; Seale et al. 2009; Oliveira et al. 2011; Woods
et al. 2011; Oliveira et al. 2013; Ruffle et al. 2015; Jones et al.
2017). Spectroscopic data reveal absorption due to molecular icesand silicate dust in the youngest protostars while more evolved
sources show fine-structure emission lines and UV-pumped polycyclic aromatic hydrocarbons (PAHs) that are typically excited in
H II regions.
New observations with the Atacama Large Millimeter/submillimeter Array (ALMA) provide maps of the continuum andmolecular emission with comparable sensitivity and resolution toobservations of Galactic clouds. For the first time, it is possible⃝
C 2019 The Author(s)Published by Oxford University Press on behalf of the Royal Astronomical Society

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Megan Reiter ,1,2‹ Omnarayani Nayak,3 Margaret Meixner3,4 and Olivia Jones3つ：[Fe II] 1.64 µm emissionを示す
4つ：H2 2.12 µm emissionを示す

両輝線：ショックのトレーサーと見なされるが、HII領域に付随しているので強いUVによる光励起
かも[Fe II]と水素再結合の比 <1：３天体全てで、光励起が卓越していることを示す
しかしながら、
0.01 <= H2/Brγ <= 1.3：４天体のうち２天体の励起にショックが寄与していることを示す
H2/Brγが高い天体は若い進化分類を持ち、その内部のsourceは降着・アウトフロー
を駆動していることを意味する

30 Dor YSO：CO bandhead 吸収を検出
若いはず
Spitzer IRS：PAHの特徴やHII領域で励起される典型的なemission lineを示す
ALMA：母分子雲に付随していることを示す
銀河系内の大質量YSOsでの検出の多くはemissionでのCO bandheadを示す（Cooper+13）
30 Dor YSOでのCO bandhead吸収の起源はよくわからない40
1

Evidence of Hubble Flow-like Motion of Young Stellar
Populations away from the Perseus Arm
Carlos G. Román-Zúñiga1,2 , Alexandre Roman-Lopes2,3 , Mauricio Tapia1,2
Jesús Hernández1 , and Valeria Ramírez-Preciado1,

Instituto de Astronomía, Universidad Nacional Autónoma de México, Unidad Académica en Ensenada, Ensenada 22860 Mexico; croman@astro.unam.mx
2
Programa de Estancias de Investigación (PREI), DGAPA-UNAM, Mexico
3
Departamento de Física y Astronomía, Universidad La Serena, La Serena, Chile
Received 2018 August 19; revised 2018 December 12; accepted 2018 December 26; published 2019 January 22

Abstract
In this Letter we present evidence of the coherent outward motion of a sample of young stars (t < 30 Myr) in the
Perseus Arm, whose apparent origin is located in the vicinity of the W3/W4/W5 complex. Using astrometric andphotometric data from the Gaia Data Release 2 catalog of an 8◦ radius ﬁeld centered near W4, we selected asample of young intermediate- to high-mass star candidates. The sample is limited to sources with parallax
uncertainties below 20% and Bayesian distance estimates within 1800 and 3100 pc. The selection includes
embedded stellar populations as well as young open clusters. Projected velocities derived from perspectivecorrected proper motions clearly suggest that the young star population emerged from the Perseus Arm, with apossible convergence zone near W3/W4/W5 region, tracing a front that expands away at a rate ofabout 15 km s-1 kpc-1.
Key words: Galaxy: kinematics and dynamics – open clusters and associations: general – stars: kinematics anddynamics – stars: massive
1. Introduction

Star clusters are formed within giant molecular clouds(GMCs) with a large diversity, likely related to the earlyorganization of the clouds and environmental factors (Lada &Lada 2003; Longmore et al. 2014). In a recent review,
Gouliermis (2018, and references therein) discussed the case ofgravitationally unbound young stellar systems, representing
GMC complex-scaled multiplex associations that may beconsidered to be the open end of an intricate, hierarchicalprocess that scales down to the formation of compact, boundclusters. In that scenario, large GMC complexes may produce alarge number of star clusters born with a variety of energy
distributions (Blaauw 1964) that, in most cases: (a) expand anddisperse, (b) can be traced through their massive (OB)members, andFor instance, the Gaia DR2 parallaxes provide distances thatare still uncertain in the 102 pc scale for the PsAm, impeding an
accurate analysis of the distribution of young stellar populations within this part of the Arm. Also, the lack of radial
velocity measurements for most of the stars in our sample
prevents a full six-dimensional position–velocity analysis at
this Galactic region. From the observed expanding motion andthe available theories in the literature, we propose threepossible scenarios.

ベクトルを戻すとW345近くの収束領域に行き着く
現在は1.5 Myrの若い埋もれたpopulationがある

1. The presence of the HB-3 supernova (SN) remnant nearW3, along with the presence of tens of OB stars in theW345 complex (see the top panel Figure 2), suggest thatSN explosions could be one possible driving mechanism in
the region, which could transfer the mechanical energy to
the cluster-gas systems. Indeed, it is known that a single SN
can imprint momentum of the order of 10 5M: km s-1 (Kim
& Ostriker 2015), providing up to 1050 erg in 10 Myr(Thornton et al. 1998). Super-bubble-type expansions via
SN often pierce and surpass the disk, depending on thehomogeneity of the local medium (Mac Low et al. 1989).
Also, most of the mechanical energy from SN events andmassive star winds is carried by ionizing radiation, which
could provide impulse for the stellar system expansion.
Gaia DR2 data could provide evidence of a champagneﬂow-type expansion of gas layers (Tenorio-Tagle 1979),
with the stars moving along with the gas.
2. Recently, Tchernyshyov et al. (2018) presented detailed gas
velocity maps and compared them to the Stationary Density
Wave model of the Milky Way spiral structure (Lin &Shu 1964), particularly near the PsAm. The study suggeststhat a spiral arm can be fed from one side by diffuse gas
causing a net outward ﬂow toward its trailing edge. The
main effect is a concentration of the dense gas where ﬂows
converge, and a dissipation of those centers after starformation, forming a divergence of the velocity ﬁeld. Thismechanism can provide a direct explanation of theobserved effect in our sample. Moreover, if gas and stars
are expelled away from the arm, aided by this mechanism,
then we should expect a net torque in the arm. If this is true,
our study presents actual evidence of the action of spiraldensity waves near the co-rotation radius in the PsAm.
3. Another possibility is that all the groups that we areconsidering are all part of a much larger association of2clusters that is expanding away as a massive unboundyoung stellar system with an age spread of about 30 Myr(considering the estimated ages of the older clusters in thesample). The driving mechanisms behind the expansion
could be directly related to the star formation process,along with gas dispersal and the dynamic evolution of thesystem, similar to what is observed in star-forming
complexes like Orion, Vela OB2, or Scorpio–Centaurus.
However, it would be necessary to determine how toadjust such proposed scenarios to the spiral arm widthscale that we report in this Letter.

結果の解釈＆現在受け入れられている銀河系での星形成シナリオへの影響：(l, b ) = (137.8, 1.3), which was estimated by projecting
backwards the vl , vb vectors of candidate members of known
open clusters, (deﬁned as sources within a small vicinity
around published centers and distances and limited tosv v < 0.1). We can see how the corrected velocity moduli
for most of the sources are in the range of 10–20 km s−1, which
is signiﬁcantly larger than the typical expansion velocities forunbound groups in other systems (e.g., Cantat-Gaudin et al.
2019; Kuhn et al. 2019; Wright & Mamajek 2018). It is clearthat the young stellar population is actually expanding away fromthe Galactic plane: a linear ﬁt to the data suggests a (projected)
Hubble-type expansion of about 15.4 km s-1 kpc-1. The
additional panel of the Figure 4 shows the equivalent plot forthe control sample, where we conﬁrm a null expansion trend,with a correlation coefﬁcient near zero. The results for the codistant control sample are equivalent, with a null expansion trend
and little or no coherence in the dot-vector plot.

=> このレターの範囲を超えている（より正確なデータが必要なので）例えば・・・

Gaia DR2の視差は10 pc scaleで不確定性が未だあり、正確な分布解析が難しい

また、radial velocityの測定がないため、6次元の位置速度解析ができていない
4. Discussion and Summary

今回観測された広がる動きと現在ある理論から、可能性のある３つシナリオを提案
The analysis of the Gaia DR2 data described above reveals ascenario where young stellar populations are moving awayfrom a location in the PsAm. Tracing back the (v , v ) vectors

While eloquent, our analysis is just a starting point. Future

1：W3付近のHB-3超新星残骸の存在：超新星爆発が駆動メカニズム
力学的エネルギーを星団-ガス系へ移す
実際、単一SNは105 Msun km s-1の運動量を押し（Kim&Ostriker 15）、
最大1050 erg in 10 Myrを与える（Thompson+98）
SNによるSuper-bubbleタイプの膨張は、ディスクを貫く（Mac Low+89）
また、SNと大質量星風からの力学的エネルギーの多くは、
ionizing radiatoinによって運ばれ、恒星系膨張への要因となる
Gaia DR2 dataはシャンパン流型のガス層の膨張の証拠（Tenorio-Tagle 79）であり、星はガスに沿って動いている。
2：Tchernyshyov+18：
詳細なガスの速度マップを示し、銀河系spiral構造の密度波モデル（Lin & Shu 64）と比較を行なっている（特にPrAm付近の）。
trailing edgeへの外側への流れを起こしているdefuseによって、片側からspiral armは供給されている。

主な効果は高密度ガスの集中（そこに流れが収束）と、星形成後の中心ガスの散逸。
それが速度場の発散を生み出している
今回の観測結果はこのメカニズムによるものと解釈できる

更に、このメカニズムによって星とガスがarmから追い出されるとすると、armでのnet torqueが
これが本当ならば我々の研究は、PsAmでのspiral密度波の作用の実際の証拠を与えている。
3：全てのグループが、かなり大きな星団アソシエーションの全てである可能性。
約30Myrで広がっている、巨大なunboundな若い恒星系のような膨張をしている
膨張の駆動メカニズム：ガスの散逸・系の力学的進化の変化による星形成過程と直接関係している（OrionやVela OB2、Scorpio-Centaurusのような星形成領域で観測されるものと似ている）=> But このシナリオをspiral armスケールにどのように適合させるかが問題である

Advance Access publication 2018 December 6

Evolution of Hubble wedges in episodic protostellar outflows

39 Evolution of Hubble wedges in episodic protostellar outflows
21School
I. Physikalisches
Universitätzu Köln,
Zülpicher
Str. CF24
77, D-50937
Köln, Germanyof Physics Institut,and Astronomy,
Cardiff
University,
Cardiff
3AA, UK
32 School of Physics and Astronomy, Cardiff University, Cardiff CF24 3AA, UK

Universitäts-Sternwarte München, Scheinerstraße 1, D-81679 München, Germany

3 Universitäts-Sternwarte München, Scheinerstraße 1, D-81679 München, Germany

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user
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Downloadedfromhttps://academic.oup.com/mnras/article-abstract/483/2/2563/5232391
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user
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2019

1‹
1
2
1
P. F. Rohde,1‹1‹ S. Walch, 1‹ D. Seifried , 1 A. P. Whitworth, 2 S. D. Clarke 1 and D.
P. F. Rohde,
S. Walch, D. Seifried , A. P. Whitworth, S. D. Clarke and D.
3
A. Hubber 3
HubberInstitut, Universität zu Köln, Zülpicher Str. 77, D-50937 Köln, Germany
1A.
I. Physikalisches

若い低質量星からのアウトフローの最近の研究：降着とアフトフローは一時的なもの
Accepted 2018 November 30. Received 2018 November 30; in original form 2018 August 23
Accepted 2018 November 30. Received 2018 November 30; in original form 2018 August 23

ABSTRACTABSTRACT

Young low-mass protostars undergo short phases of high accretion and outburst activity leading
新たに開発したsub-gridアウトフローモデル：一時的な振る舞いを考慮
Young
low-mass
protostars
short phasesof highthat
accretionand outburst activity
tolumpy
outflows.
Recent undergo
observations
have shown
the position–velocity
and leading
mass–
to lumpy
outflows.
Recentobservations
have shownthat thefeatures;
position–velocity
and bullets
mass–velocity
diagramsof suchoutflows
exhibit individualbullet-likesome of thesevelocity diagramsof suchoutflows
exhibitindividualbullet-likefeatures;assomeof thesebullets
subscribe
to a ‘Hubble
Law’
velocity
relation,and others
are manifest‘Hubblewedges’.
subscribea ‘Hubble
Law’ velocity
are manifest
as ‘Hubble
Inorder totoexplore
the originof these relation,
features,and
we others
have developed
a newepisodicwedges’.
outflow
In orderexplorethe originof these features, we have developed a new episodic outflow
GANDALF, which mimics the accretion and ejection behaviour ofmodel
fortotheSPH codeGANDALF, which mimics the accretion and ejection behaviour ofmodel for the
SPHWe
code
FU-Ori-typestars.
apply
this model to simulations of star formation, invoking two types
FU-Ori-typestars. We
apply thissymmetricmodel to simulationsof star formation,
invoking,typesandofinitial conditions:sphericallycores in solid-bodyrotation withρ ∝ twor−2
of initial conditions:symmetric
cores proportionalin solid-bodytorotation
withofρan∝Bonnor–r−2 , andsphericallysymmetricsphericallyturbulent coreswith density
the density
sphericallyturbulentcores
withparameters,
density proportional
to thedensityof an Bonnor–
Ebert
sphere.symmetric
For a wide
range ofmodel
we find that
episodicoutflows
lead toEbert sphere. Fora widerange
of andmodel
parameters,that episodic
outflows
toself-regulationof theejectedmass
momentum,andwewefindachieve
acceptable
results,leadevenself-regulationoftheejectedmass
andmomentum,andweachieve
acceptable
results,evenwith relatively low resolution. Using this model, we find that recently ejected outflow bullets
with relatively
lowwedge’
resolution.
Using
this model, werelation.
find thatHowever,recently once
ejectedoutflowbullets
producea ‘Hubble
in theposition–velocity
sucha bullethitsproducea ‘Hubble
wedge’
in the position–velocity
relation.
a bullet hitstheleading
shock front,
it decelerates
and aligns witholder However,bullets to once
form sucha ‘Hubble-law’.
the leading
shock
front, itasdecelerates
with older
bulletswhich
to forma ‘Hubble-law’.
Bullets
can beidentified
bumps in andthe aligns
mass–velocity
relation,canbe fit with a
Bullets candM/dυbe identified
asbumps
in the mass–velocity relation, which can be fit with a
−1.5
∝
υ
.
power-law,
RAD
RAD
−1.5
power-law, dM/dυRAD ∝ υRAD .
Key words: stars: formation – stars: protostars – stars: winds, outflows.
Key words: stars: formation – stars: protostars – stars: winds, outflows.

アウトフローをモデリングするのに必要なmass-resolutionを減少させる（連続的なアウトフローよりもアウトフローバーストで、ガスがより高密度になるので）と同時に、要求される計算量を減らす（アウトフローparticuleは短いoutburstで発射されるので）。

1 I N T RO D U C T I O N
1 I N T RO D U C T I O N
In the core accretion scenario for star formation, collapsing dense
In theform
core protostars,
accretion scenario
star formation,
collapsing
dense
cores
and theseforprotostars
are usuallysurrounded
cores
form protostars,
protostars
usuallybyaccretion
discs (e.g.and
Shuthese& Adams
1987;areTan
et al. surrounded
2014, andby accretion
discs (e.g.
Shu &theAdams
1987;luminosities
Tan et al. 2014,
andreferences
therein).
However,observedof suchreferences andtherein).
However,the observed
luminosities
suchprotostars,
therefore
by implication
also theiraccretionofrates,
protostars,
therefore
by implication
also theiraccretion
rates,
aretypicallyand
much
lower than
one would expect,
given
their masses
are formation
typically much
lower thanwouldsteady
expect,accretion;
given theirmassesandtime-scales,
and oneassuming
thismisand formation
andproblem’
assuming(Kenyon
steady accretion;
thismismatch
is called time-scales,‘the luminosity
et al. 1990,
1994;
match is&called‘the luminosity
problem’(Kenyonet al.can
1990,
KenyonHartmann1995). The
luminosity
problembe 1994;
mitiKenyon& Hartmann1995).theTheluminosity
problem canbe mitigated
if theaccretion fromdisc
onto the protostar
is episodic,
gateda large
if thefraction
accretionfromthe discoccuring
onto theinprotostar
is episodic,
withof theaccretionshort intense
eventswith a large
fractionof the&accretionin short intense
eventscalledoutbursts(Offner
McKee occuring2011; Dunham& Vorobyov
calledCesaroni
outburstset (Offner
McKee
Vorobyov2012;
al. 2018;&Hsieh
et al.2011;2018;Dunham
Ibryamov,&Semkov&
2012; Cesaroni
et al. 2018;
Hsieh
et al.Such
2018;
Ibryamov,&
Peneva2018; Kuffmeier
et al.
2018).
outbursts
areSemkov
observed
Peneva2018;
Kuffmeieretal.
2018).
Such
outbursts
areobserved
in FU-Orionis-type stars (FUors), which undergo a rapid increase−1in accretion
FU-Orionis-typestars∼ (FUors),
increaseyr−1 toundergo∼10−4 aMrapid
inrate, from10−7 M⊙which⊙ yr , for a−1−1
to ∼10−4
for ain accretion
rate,
from (Herbig∼ 10−7 M⊙ yr Hartmann⊙ yr ,1985;
periodof order10 years
1966;&M
Kenyonperiod of order 10 years (Herbig 1966; Hartmann & Kenyon 1985;⋆ E-mail: rohde@ph1.uni-koeln.de (PFR); seifired@ph1.uni-koel.de (SW)⋆ E-mail: rohde@ph1.uni-koeln.de (PFR); seifired@ph1.uni-koel.de (SW)

Hartmann et al. 1989; Audard et al. 2014; Safron et al. 2015; Fehér
al. 1989;
al. 2014; Safron
et al. 2015;
etHartmannal. 2017).et The
causeAudardof thisetbehaviour
is still debated,
butFehérone
et al. 2017).
Theinterplay
cause of ofthisgravitational
behaviour isandstillmagnetorotational
debated, but one
possibility
is thepossibility is(MRI;
the interplay
gravitational
magnetorotational
instabilities
Balbus &ofHawley
1991) andin thedisc (e.g. Zhu,
instabilities
Balbus& Zhu
Hawleyin Stamatellos,
the disc (e.g.WhitZhu,
Hartmann& (MRI;
Gammie2009a;
et al.1991)
2010a;
Hartmann& Gammie
Zhu etetal.
Whitworth& Hubber
2011b;2009a;
Kuffmeieral.2010a;2018).Stamatellos,
Using a large
enworth &ofHubber
2011b;
Kuffmeieret al. 2018).(SPH)
Usingsimulations
a large ensemble
Smoothed
Particle
Hydrodynamics
sembleofSmoothed
Particle
Hydrodynamics(SPH)
simulations
Lomax, Whitworth & Hubber (2016a,b) conclude that episodic acLomax,isWhitworth(2016a,b)concludethat initialepisodicaccretionnecessary &to Hubber
reproduce
the observed
stellarmass
cretion isandnecessarythe observed
stellar initialstars.
massfunction
the ratioto
ofreproduce
brown dwarfs
to hydrogen-burning
functionand the ratioof brownprotostars
dwarfs to hydrogen-burning
Most, possibly
all, forming
launch fast bipolarstars.
outMost,all, forming
protostars
launchfastetbipolar
outflows(see,possibly
e.g., the reviewsof Arceet al. (2007);Frank
al. (2014);
flows (2016),(see, e.g.,
Arce fromet al. (2007);
Frank
et al. (2014);
Bally
orthe
thereviews
recent ofresults
Samal etal. (2018)).
The
Bally (2016),
or therecentfrom
Samal et al.
(2018)).
The
inferenceis that,duringthe results
collapse,
gravitationalenergyis coninference
that, during
the collapse,
gravitationalenergyis converted
intoiskinetic
and magnetic
energy,which thendrivesandverted intothekinetic
andeithermagnetic
energy,whichthen ordrivesandcollimates
outflow,
throughmagneticpressuremagnecollimates theforces
outflow,either throughmagneticpressure or magnetocentrifugal(Blandford& Payne1982; Lynden-Bell
2003;
tocentrifugal
forcesMachida,(Blandford& Payne1982; Lynden-Bell
2003;
Pudritz
et al. 2007;
Inutsuka& Matsumoto
2008; Seifried
et al.Frank2007;etMachida,& Matsumoto
2008;removes
Seifried
etPudritz
al. 2012;
al. 2014;Inutsuka
Bally 2016).
The outflow
al. 2012; fraction
Frank etofal.the
2014;
Bally
2016). Thefrom
outflow
removesaetsignificant
angularmomentum
the star–disca significant
fractionof theangularmomentumsystem,enabling
the gasin theaccretion
disc tofrom
reachthethestar–disccentralsystem, enabling
thePudritz
gas in theaccretion
to 2007).
reach thecentralprotostar(Konigl &2000;
Pudritzdisc
et al.
Sincetheprotostar (Konigl & Pudritz 2000; Pudritz et al. 2007). Since the⃝C 2018 The Author(s)⃝C 2018 The Author(s)Publishedby Oxford University Press on behalf of the Royal Astronomical Society
Published by Oxford University Press on behalf of the Royal Astronomical Society

1. Rotating setup
一時的な降着とprotostarからのアウトフローの効果を調査
安定した、剛体回転の球対称コア（ρr-2）の中心で形成
Hubble wedges in protostellar outflows
2569
2570
P. F. Rohde et al.
Downloaded from https://academic.oup.com/mnras/article-abstract/483/2/2563/5232391 by National Astronomical Observatory of Japan user on 27 February 2019

Table 2. Parameters for the runs performed with the Rotating Setup (Section 2.4). Reading left to right, the columns give the run number, the run ID, thefeedback mechanism, the number of particles in the core (NCORE ), the sink formation density (ρSINK ), the wind opening angle (θWIND ), the launching radius(rLAUNCH ), the jet opening angle (θJET ), the fraction of the gas accreted by a protostar that is ejected in bipolar outflows (fEJECT ), the minimum radius at which
the SPH particles representing the outflow are injected (rMIN ), and the Shakura–Sunyaev viscosity parameter for MRI viscosity (αMRI ).
#Run

Feedback

NCORE
103

ρSINK
g cm−3

θWIND
radianrLAUNCH
AU

θJET
radianfEJECT

rMIN
AU

αMRI

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22

CONT:100
CONT:200
CONT:400
EPISODIC:25
EPISODIC:50
EPISODIC:100
EPISODIC:200
EPISODIC:400
RHOSINK:11
RHOSINK:12
THETAWIND:0.6
THETAWIND:0.2
RLAUNCH:14
RLAUNCH:047
THETAJET:0.05
THETAJET:0.005
FEJECT:0.2
FEJECT:0.05
RMIN:30
RMIN:10
ALPHAMRI:0.2
ALPHAMRI:0.05

Continuous
Continuous
Continuous
Episodic
Episodic
Episodic
Episodic
Episodic
Episodic
Episodic
Episodic
Episodic
Episodic
Episodic
Episodic
Episodic
Episodic
Episodic
Episodic
Episodic
Episodic
Episodic

100
200
400
25
50
100
200
400
100
100
100
100
100
100
100
100
100
100
100
100
100
100

10−10
10−10
10−10
10−10
10−10
10−10
10−10
10−10
10−11
10−12
10−10
10−10
10−10
10−10
10−10
10−10
10−10
10−10
10−10
10−10
10−10
10−10

0.4
0.4
0.4
0.4
0.4
0.4
0.4
0.4
0.4
0.4
0.6
0.2
0.4
0.4
0.4
0.4
0.4
0.4
0.4
0.4
0.4
0.4

0.07
0.07
0.07
0.07
0.07
0.07
0.07
0.07
0.07
0.07
0.07
0.07
0.14
0.047
0.07
0.07
0.07
0.07
0.07
0.07
0.07
0.07

0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.05
0.005
0.01
0.01
0.01
0.01
0.01
0.01

0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.2
0.05
0.1
0.1
0.1
0.1

20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
30
10
20
20

0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.2
0.05

3.2 Comparison between episodic and continuous outflows

Figure 3. False-colour images of the column-density in run EPISODIC:400 at times t = 2.4 kyr, t = 4 kyr and t = 16 kyr. The spatial scale increases from top
to bottom, and the circle in the bottom panel shows the initial radius of the dense core (0.015 pc). The first panel shows the outflow cavity shortly after the first
outflow event. In the second panel, the outflow breaks out of the dense core. Multiple bullets forming a chain of Herbig–Haro-like objects are seen in the third
panel.

3.1.2 Sink creation
In Runs 6, 9 and 10 (see Table 2), the number of SPH particles in
the core is held constant (at NCORE = 105 ; hence mSPH = 10−5 M⊙
and MRES = 10−3 M⊙ ) and the sink creation density is decreased
from ρSINK = 10−10 g cm−3 (Run 6) through ρSINK = 10−11 g cm−3
(Run 9) to ρSINK = 10−12 g cm−3 (Run 10). Along this sequence, thesink radius increases from rSINK = 0.9 AU (Run 6) through rSINK =2.0 AU (Run 9) to rSINK = 4.3 AU (Run 10).
Fig. 4 shows the evolution of MSINK (t) and MTOTAL (t) (top righthand panel), and POUTFLOW (t) and PTOTAL (t) (bottom right-handpanel), obtained with different ρSINK . There are some systematicchanges with increasing ρSINK , and the results are therefore notstrictly converged, even at the highest ρSINK . In particular, the downtime between outbursts is longer with lower ρSINK . However, theoverall behaviour is not strongly dependent on ρSINK . (i) At all
times, the mass of the sink particle, MSINK (t) varies by less thana few per cent. (ii) In all the simulations, the downtime between
successive outburst events increases with time. (iii) At late times(t ! 30 kyr), as ρSINK changes by a factor of 100, the total mass

escaping from the core and its envelope, MTOTAL (t), varies by atmost 10 per cent; and the total momentum escaping, PTOTAL (t), byat most 20 per cent.

3.1.3 Synopsis

Here, we compare and contrast episodic outflow feedback with
continuous outflow feedback. The continuous feedback runs (Runs
1–3, Table 2) equate the accretion rate onto the protostar (dM⋆ /dt)
to the accretion rate onto the sink particle (dMSINK /dt) – rather
than using the sub-grid model of Stamatellos, Hubber & Whitworth(2011a) and obtaining episodic accretion rate onto the protostar;
we reiterate that in the episodic approach particles are only ejectedduring an outburst (see Section 2.3). The continuous feedback runs
use NCORE ≃ 105 (Run 1), NCORE ≃ 2 × 105 (Run 2), and NCORE ≃4 × 105 (Run 3); all other parameters have their default values. The
results are compared with the episodic accretion Runs 6 and 7.
Fig. 5 shows the evolution of MSINK (t) and MTOTAL (t) (top panel),and POUTFLOW (t) and PTOTAL (t) (bottom panel), obtained with continuous and episodic outflows. There is no evidence that the runs
with continuous outflows have converged with increasing NCORE –particularly as regards the momentum carried away from the core
(blue, , and black lines on the bottom panel of Fig. 5) – and therefore we cannot safely draw any conclusions regarding the physics
of continuous outflows. The reason for non-convergence is that thecontinuous outflows are not properly resolved.
To be properly resolved, the SPH particles near the axis of theoutflow must have neighbour-lists which contain exclusively SPH
particles that are also in the outflow (and all SPH particles in theoutflow must have neighbour-lists which contain at least a significant fraction of SPH particles that are also in the outflow). In otherwords, the SPH particles in the outflow must interact hydrodynamically with one another. With continuous outflow, the rate at which
outflow SPH particles are launched may be so low that this requirement is not met; successively ejected outflow SPH particles may
be too far apart. The SPH particles in the outflow will only interacthydrodynamically with one another if they have very low-mass, andtherefore are very numerous, specificallymSPH <

Ṁ⋆ fEJECT (4π/3) rMIN
2 υ
4 N̄NEIB πθJETLAUNCH< 7 × 10−6 M⊙!

Ṁ⋆
10−6 M⊙ yr−1

(41)
"!

υLAUNCH

主要なproperty（protostarの成長速度・アウトフローに

Low NCORE means not having to follow so many SPH particles(but at the price of coarser mass resolution), and low ρSINK means
not having to follow the SPH particles to such high densities, andhence with such short timesteps (but at the price of excising thedetailed dynamics at these high densities). On both counts this reduces computing requirements. Since our outburst model produces
approximately converged results with low NCORE and low ρSINK –modulo slightly longer downtimes between outburst events – weconclude that it can be used in larger scale simulations of star formation (e.g. Clarke et al. 2017), where the computing requirementswith higher NCORE and/or higher ρSINK = 10−10 g cm−3 might not be
feasible.

よって運ばれる質量や運動量）は、数値パラメータにほとんど依存しないMNRAS 483, 2563–2580 (2019)2. Turbulent Setup
一時的な降着とprotostarからのアウトフローの効果を調査
初期にturbulentで球対称なコア（Bonnor-Ebert球に比例する密度proﬁle）の中心付近で誕生
Hubble wedges in protostellar outflows
2575
2576
P. F. Rohde2576
et al. P. F. Rohde et al.

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Downloaded from https://academic.oup.com/mnras/article-abstract/483/2/2563/5232391 by National Astronomical Observatory of Japan user on 27 Febru

Figure 9. Evolution of the accretion
onto theparticle, Ṁ(t) (green),
the protostar,labels, A–F,
to theoutflow
Figure 9.rates
Evolution
ofsinkthe accretionrates
the sinkand
particle,
ṀSINK (t)Ṁ(green),andThethe protostar,Ṁ⋆correspond(t) (blue). The
labels,
A–F, correspond to the outflow⋆ (t) (blue).
SINK ontobullets formed in the individual
outbursts
Figs.
8 and 10).
Note thattheFigs.
time8resolution
in thisfigureis tooresolution
coarse toin
fully
very
shorttooutbursts.
bullets
formed(seein theindividual
outbursts(see
and 10). Notethatthe time
thisresolve
figure isthetoo
coarsefully resolve the very short outbursts.

(2001); Tafalla et al. (2004);
Santiago-Garcı́a
et al. (2009);
Wang(2001);
Tafalla et al. (2004);
Santiago-Garcı́aet4.2
al. Mass–velocity(2009); Wang Relation
4.2 Mass–velocity Relation
et al. (2014), we constructetPV-diagrams,
false-colour
plots of i.e. false-colour plots ofal. (2014), wei.e.
construct
PV-diagrams,
The left-hand panels of Fig.
show MV-diagramsfor10theleft MV-diagrams
lobe
The10left-handpanels of Fig.
show
for the left lobeof the simulated outflow, ofi.e.theplotsofsimulated
outflow, i.e. plots of"MPIXEL =

d 2M
d 2M
"r"M
"υPIXEL"r "υRADRAD =dr dυRADdr dυRAD

(46)

"M =

dM
(46)
"υRAD
dυRAD

"M =

dM
"υRAD
dυRAD

(47)

(47)

against υRAD , at the sameagainst
times υasRADthein the, atPV-diagrams
the same times
as rightthe PV-diagrams in the rightEach point hand
represents
masspoint
in arepresents
radial velocity
panels.theEach
the mass in a radial velocity
on the (r, υRAD ) plane. Here,r is(r,radialand υrRAD
is radialon theυRADdistance,) plane. Here,is radialdistance,handand υpanels.
isradialRAD−1−1, and only
pointsto points≥22 that correspond to ≥22interval"υvelocity= 2thatkmcorresponds , and only"υRAD
RAD = 2 km s intervalvelocity, both measured fromthe centreof mass. from
For thevelocity,
both measured
thevelocity
centre of mass.
For the−4−4
are considered.
At low
υRAD ! At low velocities, υRAD !
10 M⊙ )SPH
M⊙velocities,) are considered.
articles (≥ 10
0.56akms−1 .ofFor
axis we take 180 bins withwidth"υbins
0.56articles
km
s−1(≥
. For
axisa wetakeof180
with
width
"υRAD =SPH
RAD =
−1
−1
plots can bewitha single
power80 kmshellss , the, theplots
can beshallow
fitted wellwith a single shallow power80fitted
km s well
the spatial axis, we take the180spatial
sphericallyaround symmetricaxis, symmetric
we take 180shells
sphericallyaroundlaw,
law,
the centre of mass with athewidthof of"rmass= 0.0056
and consider
centrewith apcwidthof "r = 0.0056
pc and consider
only particles with radialonly
outflow
velocities
than the velocities
escape largerdM
particleswith larger
radial outflow
than the −γ
escape
dM
−γ
∝
,
(48)
∝ υRAD,(48)
RADM⊙ ,
3.9inMthis
velocity (equation (37)). velocity
Note that(equationin this case
MTOTAL= υ3.9(37)).
Note =
that⊙ , case M
dυTOTAL
dυRAD
RAD
−1
−1
effectively
so the escape velocity atso0.1
is 0.58velocity
km s .atThis
thepcescape
0.1 pcis 0.58 km s . This effectively≃ 1.5,
good agreement
observed
simulatedwith γ with
≃ 1.5,
in good andagreement
withvalues
observed and simulated values
constrains our analysis toconstrains
the outflowour
cones.
As atofinal
step, wecones.
use As awith
analysisthe outflow
finalγ step,
weinuseet al. 1981; Lada(Kuiper& Fichet1996;
Bachiller
1999;Bachiller & Tafalla 1999;
al. 1981;
Lada&&Tafalla
Fich 1996;smoothinga kernel density estimatora tocompute"M
with a smoothingkerneldensityestimator
to acompute"MPIXEL ,(Kuiper
PIXEL , with
Richer et al. 2000; Keegan& Downes
2005;Keegan
Arce et&al.Downes
2007; Liu
Richeret al. 2000;
2005; Arce et al. 2007; Liulength obtained using ”Scott’s(Scott1992).
lengthRule”
obtainedusing”Scott’s Rule” (Scott 1992).
et
Li etofal. 2018).
et al. 2017; Li et al. 2018).
Fig. 10 (right-hand side) Fig.
shows
diagramsside)
for theleft lobeof
10PV(right-handshows
PV diagrams
foral.the2017;
left lobe
Someassociatedobservers have reported
knee, at havehigh velocities,
Some aobservers
reported a aboveknee, at high velocities, above
Figure 8. Column density images of the Turbulent Setup, at t = 115, 117, 120 and 122 kyr. The circle indicates the initial radiusof the core,andsamethe viewing
the outflow
at thetimes
shownaton
8. Featuresassociatedthe asoutflow
theFig.
sametimes as shown
on Fig. 8. Features
which
the slopeabruptlywhichbecomes
steeper. We
find nomuch
evi- steeper. We find no evithe muchslope abruptly
becomesangle is chosen so that the outflow axis is approximately horizontal. The bullets are labelled AL/R through EL/R for the corresponding
left and rightlobe,within marked
with the individualbullets
are
A, B, C,etc., arein both
figures.
the individualbullets
markedA, B, C, etc.,
in both
figures.
dence
for this,panel
possibly because
ourthis,simulation
unable todence forpossiblyisbecause
ourresolve
simulation is unable
no evito resolvW
order of increasing age (see Fig. 9). The time series, from top to bottom, shows the end of a cycle of a bullet, here bullet DL , whenhits the leadingshock
The itPV-diagramat 115kyr
shown in theattop
panel
Theis PV-diagram
115right-handkyr is shownin the top
right-handfront. Bullet DL hits the leading shock front with high velocity, overtakes the older bullets and decelerates. In the last panel, theofnewly
aFig. 10.
small
L is inFig. ejected
10. Atbullet
this Estage,
A, At
B, thisand stage,
C define
the Hubble
ofbulletsbullets
A, B, and C thedefinetheamounts
Hubble of mass involved.
comparable position as former bullet DL in the first frame.
the bullets are manifest as small local peaks.
has at ∼25On
Law. The oldest bullet, A,
moves
at ∼25s−1 andanddiagram,has
Law.
The slowest,
oldest bullet,
A,km
moves
slowest,
kmthe
s−1MV
The oldest
only reached ∼0.3 pc. Bullets
B and C∼0.3
appearareCinappear merged,
only reached
pc. merged,
Bullets Bbut
andbutbullet,
are inA, has the lowest velocity, and the youngest bullet,−5F,fasterhas thethan
highest.
The first two bullets interact with the collapsing dense core material∼2 × 10andt = 150 kyr. ṀSINK is relatively constant,factbetween
kinematicallyseparate.
moves outwards
fasterB thanA, outwards
atfact Bkinematicallyseparate.
moves
A, atThere are two reasons for this. (a) The protostellar−1and so the later bullets are launched at highermass,M⋆ (t) increases,
and are thus not visible in Fig. 8. The timespan from 115 kyr to 122
tends
tosdecrease
overreachedtime.
∼5 × 10−6 M⊙ yr−1 . The accretion rate∼30, and has
∼0.46
moves
outwardskm
andChasreached∼0.46fasterpc. C moves
outwards
faster
∼30 kms−1 ,pc.
−1
velocityequation (16)). (b) The later bullets encounter lesskyr is chosen to capture the end of a cycle of an outflow bullet, here
It drops briefly, following an outburst, because
outburst
thehasB,reached, andBulletD moves∼0.52 pc.
than B, theat ∼40km sheats, andhas reached
Bullet (seeD movesthan
at ∼40 ∼0.52
km s−1pc.
−1 ofresistancebecausebullet D, when it hits the leading shock front. This cycle happens
accretion disc (cf. Lomax et al. 2014, outwards2015). The, outwards
but has only
beenkmgoing
it going
at accretion∼80 km sratebut ∼6haskyr,onlysobeen
for ∼6 kyr,so it earlier bullets have cleared the way for them.
at ∼80s−1 , for−1
−7
in a similar fashion for all other bullets, except the first bullet A.
10hit
M
, but
the protostar is low in the quiescent phase,⊙ yr
has Ṁ
notyettheleadingandhitbeen
decelerated.
E decelerated. Bullet E
hasshock
not yetthe leading
shockBullet
and been⋆ =This is the first bullet that breaks out of the core and survives as a
Notethelaunched,time resapproaches 10−3 M⊙ yr−1 during an outburst.
has only
justthat
been
thebeenlast launched,∼1 kyr; thewithin
outburst
has within
only justthe atlast ∼1 kyr; the outburst at
5 DISCUSSION
coherent structure. Bullets B and C have higher velocity and haveolution in Fig. 9 is too coarse to resolve ∼114
the verykyrshortthat outbursts.
launches EThecan bekyr
seenFig. 9. E can be seen on Fig. 9.
∼114
thatonlaunches

一時的アウトフロー：
pcスケールの長いS字型のbulletのchain
を生む=> HH天体と同一であると見なした

Hubble wedges in protostellar outflows

2577

bulletのPV図は２つの特徴を示す：
・初期に排出されたbulletは低視線速度で放出、
leading shockで減速されている。bulletはradial
distanceに比例するradial velocityを持つ（ハッブル則に従う）
・最近に放たれたbulletは速い視線速度を持ち、shock frontで未だに減速していない。
bulletsはハッブルwedgeを形作る

アウトフロー中のガスの質量-速度の関係：dM/dvRAD

vRAD-1.5でだいたいﬁtできる=> 観測値によく合う。
個々のbullet：この関係に従う小さなbumpとして現れる

© 2019.©The
AmericanAstronomical
Society. Society.
All rights
2019.
The American
Astronomical
Allreserved.
rights reserved.

Planetesimals
Perturbed
by abyGiant
Planetin ainGas
Disk
Shock-generating
Planetesimals
Perturbed
a Giant
Planeta Gas
Disk
33Shock-generating
1

1
2
2
3
3
4
M. Nagasawa, 1K. K.
, H.2Tanaka, H.2Nomura, 3T. Nakamoto, and3, H.
M. Nagasawa, K.Tanaka
K. Tanaka, H. Tanaka, H. Nomura, T. Nakamoto
andMiura
H. Miura4

1
Departmentof Physics,
SchoolSchoolof Medicine,
KurumeUniversity,
67 Asahi-machi,
Kurume-city,
Fukuoka
830-0011,
Japan;Japan;
nagasawa_makiko@med.kurume-u.ac.jp
Departmentof Physics,of Medicine,
KurumeUniversity,
67 Asahi-machi,
Kurume-city,
Fukuoka
830-0011,
nagasawa_makiko@med.kurume-u.ac.jp
22
AstronomicalInstitute,
TohokuUniversity,
6-3 Aramaki,
Aoba-ku
Sendai,
MiyagiMiyagi
980-8578,
Japan Japan
AstronomicalInstitute,
TohokuUniversity,
6-3 Aramaki,
Aoba-ku
Sendai,
980-8578,
33Departmentof Earthand Planetary
Sciences,TokyoTokyo
Instituteof Technology,
2-12-1,2-12-1,
Ookayama,
Meguro-ku,
TokyoTokyo
152-8551,
Japan Japan
Departmentof Earthand Planetary
Sciences,
Instituteof Technology,
Ookayama,
Meguro-ku,
152-8551,
4
4Graduate
SchoolSchoolof Natural
Sciences,
NagoyaCity University,
Yamanohata
1, Mizuho-cho,
Mizuho-ku,
Nagoya467-8501,
Japan Japan
Graduateof Natural
Sciences,
NagoyaCity University,
Yamanohata
1, Mizuho-cho,
Mizuho-ku,
Nagoya467-8501,
Received
2018
August21;
revised2018
October
31;
accepted
2018
December
9;
published
2019
January
25
Received 2018 August 21; revised 2018 October 31; accepted 2018 December 9; published 2019 January 25

Abstract
Abstract
We examinedthe excitationsof planetesimals
causedby theof a giant
planetplanet
in a protoplanetarygas gasWe examinedthe excitationsof planetesimals
causedbyresonances
the resonancesof a giant
in a protoplanetary
disk. disk.
The Thehighlyexcitedplanetesimals
generate
bow bow
shocks,the mechanismof which
results
in chondrule
highlyexcitedplanetesimals
generateshocks,the mechanismof which
results
in chondrule
formation,
crystallizationof silicate
dust, dust,
and evaporationof icyof planetesimals.
The Theplanetesimals
beyond
2:1 2:1
formation,
crystallizationof silicate
and evaporation
icy planetesimals.
planetesimals
beyondresonance
migrateowing
to thetogas
and obtainthe maximum
eccentricity
around3:1 resonance,
whichwhich
is isresonance
migrateowing
the draggas dragand obtainthe maximum
eccentricity
around3:1 resonance,
locatedat approximately
half half
the planetary
distance.
The Theeccentricity
depends
on theof thelocatedat approximately
the planetary
distance.
eccentricity
depends
on parameters
the parametersof theplanetesimals
and theplanet,such suchas sizeand theof theofdisk.
The maximum
planetesimals
and Jovian
the Jovian
planet,as andsize location,and location,
andgasthe density
gas density
the disk.
The maximum
theincaserelative
velocityof a 100planetesimalwith withrespect
to thetogas
up toup∼12
km s−1the ofcase ofrelative
velocityof akm100sized
km sizedplanetesimal
respect
thediskgas reaches
disk reaches
to ∼12
kmins−1
Jupiterowing
to secularresonance,
whichwhich
occursbecauseof theofdisk’s
gravity.
We ﬁnda Jovian-massplanetplanet
Jupiterowing
to secularresonance,
occursbecausethe disk’s
gravity.
We thatﬁndifthat
if a Jovian-mass
is locatedwithin10 au,10thelargerlarger
than than
100 kmsufﬁcientvelocity
to cause
the meltingof ofis locatedwithinau, planetesimals
the planetesimals
100gainkm gainsufﬁcientvelocity
to cause
the melting
chondruleprecursors
and crystallizationof theofsilicate.
The maximum
velocity
is higher
for large
planetesimals
and andchondruleprecursors
and crystallization
the silicate.
The maximum
velocity
is higher
for large
planetesimals
eccentric
planets.
Planetesimals
are trapped
temporarily
in theinresonancesand continue
to havehigh highspeedspeed
over overeccentric
planets.
Planetesimals
are trapped
temporarily
the resonancesand continue
to have1 Myrafter after
the formationof a of
Jovianplanet.
This Thisdurationﬁts into
the timescaleof chondrule
formation
1 Myrthe formationa Jovianplanet.
durationﬁts into
the timescaleof chondrule
formationsuggestedby thedata. data.
The evaporationof icyofplanetesimals
occurswhenwhena Jovianplanetplanet
is locatedwithinsuggestedbyisotopic
the isotopic
The evaporation
icy planetesimals
occursa Jovian
is locatedwithin15 au.15This
mechanism
can benewa newindicatorof planet
formation
in exosystems
if somemolecules
ejectedfrom fromau. Thismechanismcana beindicatorof planet
formation
in exosystems
if somemolecules
ejectedicy planetesimals
are detected.
icy planetesimals
are detected.
Key words:
meteorites,
meteors,
meteoroids– minorplanets,
asteroids:
general– planets
and satellites:
dynamical
Key words: meteorites,
meteors,
meteoroids– minorplanets,
asteroids:
general– planets
and satellites:
dynamical
evolutionand stability– planets
and satellites:
formation– shock
waves
evolutionand stability– planets
and satellites:
formation– shockwaves
1. Introduction
system,whichwhich
is normallysimilarto theto rotational
speedspeedof of
1. Introduction
system,is normallysimilarthe rotational
the ascending
nodesnodesof planets,
it allows
the inclinationof theof thethe ascendingof planets,
it allows
the inclination
The observationof anofasteroid
belt shows
depletionor piling
The observation
an asteroid
belt shows
depletionor pilingasteroid
to oscillatewith withlargelarge
amplitude.
The inner
boundary
asteroid
to oscillate
amplitude.
The inner
boundary
up ofupmaterials
dependingon theof planet
resonances.
of materials
dependingonlocation
the locationof planet
resonances.
of thebelt beltof current
asteroids(∼2 au)of mainthe mainof current
asteroids(∼2 isau) mainly
is mainly
The Theresonanceswith with
Jupiterare especially
noticeable.
Asterresonances
Jupiterare especially
noticeable.
Asterdeterminedby theresonances
relatedto theto rotation
determinedby secular
the secularresonances
relatedthe rotation
oids oids
betweenthe Jovian
2:1 resonance(3.3 (3.3au) and
betweenthe Jovian
2:1 resonanceau) Jupiterand Jupiterof theperiastronand andascendingnodenodeof Saturncausedby byoftheperiastronascendingofSaturncaused(5.2 au)have
currently
dispersed
exceptforobjects
trappedin(5.2 au) have currently dispersed except for objects trapped in
Jupiter.
WhenWhenthe primordialgas disk
the eigenfrequenJupiter.
the primordialgas exists,
disk exists,
the eigenfrequenresonances(e.g.,(e.g.,
Trojansand Hildas).
Migrationof asteroids
resonances
Trojansand Hildas).
Migrationof asteroids
theofsystem
almostcoincidewith withthe rotational
speedsof ofcies
the system
almostcoincide
the rotational
speeds(planetesimals)causedby gasaccounts
for the(planetesimals)causedby draggas dragaccounts
forloss
the from
loss from cies ofof planets
causedby gravityof theofdisk.
In suchathe periastraof planets
causedby gravity
the disk.
In suchathe region
beyond2:1 resonanceif theifprotoplanetary
disk disk
is is the periastra
the region
beyond2:1 resonancethe protoplanetary
67the resonancerelatedto Jupiteris mosteffectivein in
7
situation,
the resonancerelatedto Jupiteris mosteffective
yr afterthe formationof Jupiter(Ida &
preserved
for 10yr afterthe formationof Jupiter(Ida & situation,
preserved
for–10
106–10of theof theThe Thedisk disk
the excitationof eccentricities
the eccentricities
of asteroids.
the asteroids.
Lin 1996;
Marzari
et al.et1997;
Weidenschilling
et al.et1998;
Lin 1996;
Marzarial. 1997;
Weidenschillingal. 1998; the excitation
shouldnot bewhenwhenwe consider
the theself-gravity
shouldnotneglected
be neglected
we consider
Marzari& Weidenschilling2002).
Duringthe migration,
the the self-gravity
Marzari& Weidenschilling2002).
Duringthe migration,of planetesimals
experiencing
gas drag.
Nagasawa
evolutionof planetesimals
experiencing
gas drag.
Nagasawa
planetesimals
pass passthroughmanymany
Jovianresonances,whichwhich evolution
planetesimals
through
Jovianresonances,
showedthat thesecularresonance,
whichwhichal. (2014)
showedthatJovian
the Jovian
secularresonance,
exciteexcite
the eccentricitiesof theTheseTheseeccentrithe eccentricitiesof planetesimals.
the planetesimals.
eccentri- et al.et(2014)
owing
to thetogas
gravity,excitesthe 300owing
the diskgas diskgravity,excites
the km300sized
km sized
citiescities
are further
boostedat theatlocationof 2:1ofresonance,
and and arisesarises
are further
boostedthe location
2:1 resonance,
up toupvrelto20
km s−11). 1).
planetesimals
vrel20
km(Figures−1 (Figure
they theynormally
reachreachas highas e∼0.3–0.6
at approximately
normally
as highas e∼0.3–0.6
at approximately planetesimals
supersonicplanetesimals,
whichwhichappearfollowing
the thesupersonicplanetesimals,
appearfollowing
km s−1
2–3 au,theyobtaina velocity
of vrelof8
kmrelative
s−1 relative The The
2–3thatau,is,
thatis, theyobtaina velocity
vrel8of a of
Jovianplanet,causecause
severalinteresting
effects.
formationa Jovianplanet,severalinteresting
effects.
to the(Marzari& Weidenschilling2002).
Secularto gasthe diskgas disk(Marzari& Weidenschilling2002).
Secular formation
wavewavegeneratedby theis wellknown
The shockgeneratedbyplanetesimals
the planetesimals
is wellknown
resonance
is known
to havea strong
effecteffecton theresonance
is known
to havea strong
on asteroidal
the asteroidal The shockmechanismsof chondrules,
whichwhich
are areas ofonetheofformation
the formation
mechanismsof chondrules,
orbit orbit
in thegas disk(e.g.,(e.g.,
Heppenheimer
1980;1980; as one
in primordial
the primordialgas disk
Heppenheimer
mm sized
spherical
grainsgrains
commonly
foundfoundin primitive
mm sized
spherical
commonlyin primitive
WardWard
1981;1981;
LecarLecar& Franklin
1997).
The secularresonances& Franklin
1997).
The secularresonances 0.1–10.1–1
In thebelt regionof themeteorites.
In asteroid
the asteroid
belt regionof minimum-mass
the minimum-mass
are related
to thetomotionsof theofpericenterand theare related
the motions
the pericenterandascending
the ascending meteorites.
−10 −10 −3(∼10(∼10g cm g cm), −3a ),velocityof 10km s−1be be
a velocityof 10km would
s−1 would
nodesnodesof thePeriastra
and andnodesnodesof objects
rotaterotate disk diskof objects.
the objects.
Periastraof objects
for themeltingof 1 mmsizedsized
dust dust(Iida (Iidanecessaryfor complete
the complete
meltingof 1 mmowing
to thetogravity
of otherplanets
and theWhenWhen
the the necessary
owing
the gravity
of otherplanets
anddisk.
the disk.
In Figure
1, we1,show
the conditions
requiredto to
al. 2001).
In Figure
we show
the conditions
requiredrotational
speedspeedof theof anofasteroid
is closeto to et al.et2001).
rotationalof periastronthe periastronan asteroid
is closethe meltingof chondrule
precursors(1900(1900
K) andthe meltingof chondrule
precursorsK) theand thethe eigenfrequenciesof theofsystem,
whichwhich
is normallysimilarto to causecause
the eigenfrequencies
the system,
is normallysimilarrequired
for theinitiationof vaporizationof ofthe rotational
speedspeedof theofperiastraof planets,
the eccentricity
conditions
required
for theinitiationof vaporization
the rotational
the periastraof planets,
the eccentricity conditions(2100(2100K) (see
Section4). In4).theIn outerregion,the theof theofasteroid
oscillateswith withlargelarge
amplitude.
It corresponds
to to chondruleschondrulesK) (see
Sectionthe outerregion,the asteroid
oscillates
amplitude.
It corresponds
velocities
becomehigherbecausethe gasis is
the transferof themomentumof theto therequired
velocities
becomehigherbecausethe density
gas density
the transfer
of angular
the angularmomentumof planet
the planet
to the required
The Themaximum
relative
velocitiesof 300asteroid.
Similarly,
whenwhen
the rotational
speedspeedof theofascending
maximum
relative
velocitiesof km
300 sized
km sizedasteroid.
Similarly,
the rotational
the ascending small.small.
excitedby Jupiterare indicatedby circles.
To To
nodenodeof anofasteroid
is closeto theof theplanetesimals
excitedby Jupiterare indicatedby circles.
an asteroid
is closeto eigenfrequencies
the eigenfrequenciesof the planetesimals
1

ALMA Observations of Ethyl Formate toward Orion KL
1

Yaping Peng1,2, V. M. Rivilla3, Li Zhang1, J. X. Ge4, and Bing Zhou1,2

Department of Astronomy, Yunnan University, and Key Laboratory of Astroparticle Physics of Yunnan Province, Kunming, 650091, Peopleʼs Republic of China
pyp893@163.com, lizhang@ynu.edu.cn, bingzhoukm@126.com
2
College of Science, Yunnan Agricultural University, Kunming, 650201, Peopleʼs Republic of China
3
INAF-Osservatorio Astroﬁsico di Arcetri, Largo Enrico Fermi 5, I-50125, Firenze, Italia; rivilla@arcetri.astro.it
4
Departamento de Astronomía, Universidad de Chile, Camino el Observatorio 1515, Las Condes, Santiago, Chile; gejixing666@gmail.com
Received 2018 February 2; revised 2018 December 4; accepted 2018 December 5; published 2019 February 5

Abstract
Orion KL is one of the prime templates of astrochemical and prebiotic chemical studies. We wish to explore moreorganic molecules with increasing complexity in this region. In particular, we have searched for one of the mostcomplex organic molecules detected in space so far, ethyl formate (C2H5OCHO). This species is the next step inchemical complexity after the simplest member of esters (methyl formate, CH3OCHO). The mechanisms leading to