星形成ゼミ 2015/ 6/19 Newsletter #269の16–20本目!

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16. “Ice chemistry in starless molecular cores” !
J. Kalv ̄ans!
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Accepted by ApJ!
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http://arxiv.org/pdf/1504.06065!
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17. “A Ring of C2H in the Molecular Disk Orbiting TW Hya” !
Joel H. Kastner, Chunhua Qi, Uma Gorti, Pierre Hily-Blant, Karin Oberg, Thierry Forveille,!
Sean Andrews, David Wilner!
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Accepted by ApJ!
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http://arxiv.org/pdf/1504.05980!

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18. “Formation of Super-Earth Mass Planets at 125–250 AU from a Solar-type Star”!
Scott J. Kenyon and Benjamin C. Bromley!
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Accepted by Astrophysical Journal!
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http://arxiv.org/pdf/1501.05659!

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19. “Evidence for Decay of Turbulence by MHD Shocks in Molecular Clouds via CO
Emission”!
Rebecca L. Larson, Neal J. Evans II, Joel D. Green, and Yao-Lun Yang!
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Accepted by The Astrophysical Journal!
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http://arxiv.org/pdf/1505.00847!
20. “Smoothed particle magnetohydrodynamic simulations of protostellar outflows withmis- aligned magnetic field and rotation axes” !
Benjamin T. Lewis, Matthew R. Bate, and Daniel J. Price!
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Accepted by MNRAS!
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http://arxiv.org/pdf/1504.08322v1!

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arXiv:1504.06065v1 [astro-ph.GA] 23 Apr 2015

Ice chemistry in starless molecular cores
J. Kalvāns

Engineering Research Institute ”Ventspils International Radio Astronomy Center” of Ventspils University
16. “Ice chemistry in starless College,
molecularcores”!
Inzenieru
101, Ventspils,
Latvia, LV-3601
juris.kalvans@venta.lv
J. Kalv ̄ans!

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Accepted by ApJ!
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http://arxiv.org/pdf/1504.06065!
ABSTRACTStarless molecular cores are natural laboratories for interstellar molecular chemistry research.
The chemistry of ices in such objects was investigated with a three-phase (gas, surface, andmantle) model. We considered the center part of five starless cores, with their physical conditions derived from observations. The ice chemistry of oxygen, nitrogen, sulfur, and complex
organic molecules (COMs) was analyzed. We found that an ice-depth dimension, measured,e.g., in monolayers, is essential for modeling of chemistry in interstellar ices. Particularly, theH2 O:CO:CO2 :N2 :NH3 ice abundance ratio regulates the production and destruction of minor
species. It is suggested that photodesorption during core collapse period is responsible for highabundance of interstellar H2 O2 and O2 H, and other species synthesized on the surface. The
calculated abundances of COMs in ice were compared to observed gas-phase values. Smaller activation barriers for CO and H2 CO hydrogenation may help explain the production of a numberof COMs. The observed abundance of methyl formate HCOOCH3 could be reproduced witha 1kyr, 20K temperature spike. Possible desorption mechanisms, relevant for COMs, are gas
turbulence (ice exposure to interstellar photons) or a weak shock within the cloud core (grain
collisions). To reproduce the observed COM abundances with the present 0D model, 1-10% of
ice mass needs to be sublimated. We estimate that the lifetime for starless cores likely does notexceed 1Myr. Taurus cores are likely to be younger than their counterparts in most other clouds.
Subject headings: astrochemistry — molecular processes — ISM: clouds — ISM: abundances — ISM:
individual objects (CB 17, CB 26, CB 27, B 68)

relevant to actual cores. The modeling of surface chemistry in starless cores has a long history.
Low-mass interstellar molecular clouds, such
Important papers that have presented significant＞固相上での化学進化の計算!
as the Bok globules, are a model case for cloud
advances in the field include Watson & Salpeter
structure andstar-formation
studies,CB17L,
thanks to CB26,(1972);
Allen &B68）の中心での観測値!
Robinson (1977); Pickles & Williams＞５つのStarlesscore（CB17S,
CB27,
their relative simplicity and proximity (Hartmann(1977a,b); Tielens & Hagen (1982); D’Hendecourt et al.
2009). For astrochemistry, stable starless cores(1985); Brown & Millar (1989); Brown (1990);＞固相化学を原子種(O, N, S, complex organic molecules[COM])で解析!
within these clouds are particularly interesting.
Hasegawa et al. (1992). A model for small, diﬀuse
They are suﬃciently dense for a significant mass ofclouds (not the starless core) with surface chemice to accumulate onto the grains, supposedly notistry has been presented by Turner (1998). Such
disturbed by gravitational contraction motions.
＞固相の層構造が、星間固体での化学反応のモデリングの本質である!
two-phase models with constant physical paramThus, modeling of surface chemistry can be simeters have also been used in recent papers (e.g.,
plified to calculations that consider constant, yet
ー固相上の化学反応には特に複層構造[(sub)layer]に強い依存性がある!
Du et al. 2012; Vasyunin & Herbst 2013b).
realistic physical conditions.
Starless cores with physical conditions derived
ー単層での計算は、星間固体での表面化学反応を再現するには不十分である（特に!
The aim of the present paper is to study thefrom actual observations have also been modeled
evolution of the chemical composition of ices in(Du et al. 2012; Maret et al. 2013; Lippok et al.
minor speciesでは）!
starless cores with physical conditions that are
1.

Introduction!

ー特にH2O:CO:CO2: N2:NH3の固体の存在量比は、minor speciesの生成と破壊を調整!
1

ーコアの収縮期の光乖離はH2O2,O2H,他の分子種の高い存在量比の原因であると示唆される。!
ー固相上のCOMsの計算された存在量は気相上の観測された値と比較した。!
ーCOとH2COの水素生成(Hydrogeneration)の低い励起エネルギーは、おそらく多くのCOMsの生成を説明する助けになる。!
ーHCOOCH3の観測された存在量は、1kyr, 20Kのspikeで再現できる。!
ー考えられるCOMsの破壊のメカニズムは、ガスの乱流や弱いショックである。!
ーH2O:CO固体の存在量比で年齢を推定するには危険である。!
ーCOはダストの外側の層にあることが多く、気相や他の分子種に容易に変化する!

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interstellar photonsやlow-velocity shockによる mild heating によって!

＞観測されたCOMsの存在量を0D modelで再現し、1-10%の固体質量が昇華する必要がある。!
ーO2とH2O2がOの主なreservoirs (H2OやCO2を除いて)であることを見つけた!
ーstar less core の存在期間(lifetime)は1Myrを超えないと推定した!
ページ 2/10

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＞Taurusは他の分子雲に対して若そうである!
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ーCO2:H2O固体存在比が低い。（44%かそれ以下）!

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ー既存のモデルでは650kyr (CB17S core)という値が出るが!

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<1Myrということだと考えられる!
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180

ML

160

Other (1)

140

180

CB 17 SN2 (1)H2O (1)Other (2)H2O (1)Other (2)100

CO (2)

80
60
40

60
CO2 (3)NH3 (3)CO (3)

2040

H2O (3)t, Myr

0
1.0
180

1.5

2.0

ML
Other (1)

80

40

0
1.5

60

ML

2.0

20

t, Myr

2.5

3.0

180

ML

160

Other (1)Other (1)Other (2)CO2 (1)N2 (2)CO (2)

CO2 (2)H2O (2)Other (3)
CO (3)

CO2 (3)NH3 (3)t, MyrH2O (3)1.0

3.5

SurfaceN2 (1)CO (1)H2O (1)

1.5

B 68

2.0

2.5

3.0

3.5

SurfaceN2 (1)CO (1)

120

H2O (1)N2 (2)

Other (2)100

CO2 (1)

CO (2)

80

40t, Myr
3.0

CB 27

0

3.5

140

60

2.5

40

CO2 (3)
H2O (3)1.0

100

CO2 (2)NH3 (3)CO (3)

20

2.0

80

H2O (2)Other (3)

1.5

140

CO2 (1)N2 (2)CO (2)

1.0

120

H2O (1)Other (2)100

H2O (3)160
Surface

CO2 (3)NH3 (3)CO (3)

0180

N2 (1)

CO2 (2)H2O (2)Other (3)20

3.5

CO (1)

120

60

3.0

CB 26

160
140

2.5

CO2 (1)N2 (2)CO (2)

80

CO2 (2)H2O (2)Other (3)SurfaceN2 (1)CO (1)

120

CO2 (1)N2 (2)

100

CB 17 L

Other (1)140

CO (1)

120

ML

160

Surface

CO2 (2)H2O (2)Other (3)CO2 (3)NH3 (3)CO (3)

20

H2O (3)t, Myr

0
1.0

1.5

2.0

2.5

3.0

3.5

Fig. 2.— Calculated ice thickness and abundance in MLs for major species in the sublayers for the modeled
cloud cores. The number in parenthesis indicates the number of the respective sublayer, while ‘Other’ stands
for all other icy species in that sublayer. The vertical gray line indicates t50 for each model.

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Table 1: The constant physical parameters of modeled starless cores during their stable Phase 2.
Core
CB 17 S - SMM1
CB 17 L - SMM
CB 26 - SMM
CB 27 - SMM
B 68 - SMM

nH,0 , cm−3
2.3E+5
1.3E+5
8.7E+4
1.3E+5
4.0E+5Observational data10r0 , AUr1 , AUηNout , cm−2
9.5E+33.0E+44.9
01.1E+4
3.0E+4
5.0
3.6E+20
8.0E+3
4.0E+43.0
2.2E+20
1.3E+4
6.6E+4
6.0
3.1E+20
7.0E+3
2.7E+4
5.0
3.0E+20

Ref.
Sa
Lb
L
L
L

Calculated data
AV , mag
T , K t1 , kyr
13.8
8.2
1465
9.1
9.2
1451
6.5
11.1
1437
9.5
8.9
1451
17.6
7.9
1482

Note.—Assumed physical parameters: nH,0 –density at the center of the core; r0 –radius of the central density plateau; η–power-law slope for density; r1 –radius of the region (core) in consideration; Nout –column density of the surrounding cloud.
Calculated parameter t1 is the length of the cloud core collapse Phase 1.
a Schmalzl et al. (2014)b Lippok et al. (2013)

ページ 3/10

Table 4: Changes in reactions respective to the original network by Laas et al. (2011).
No. New gas phase reactionsaαβγ Reference
1
CH2 OH + H −→ CH3 + OH
1.6E-1000 NIST
2
CH2 OH + O −→ H2 CO + OH
1.5E-1000 NIST
3
CH2 OH + CH3 −→ H2 CO + CH4 1.4E-10
0
0 NIST
4
CH2 OH + CH3 −→ C2 H5 OH
1.0E-15 -3.00 0 Vasyunin & Herbst (2013b)b
No. New surface (ice) reactions
EA , K
Reference5
H + HCO −→ CO + H20This work
6
OH + HCO −→ CO + H2 O
0This work
7
NH2 + HCO −→ CO + NH30This work8
H2 + HCO −→ CH3 O
2100c
This work
9
OH + SO −→ SO2 + H
0
Gas phase
10 O + HS −→ S + OH
956
Gas phase
11 O + HS −→ SO + H
0
Gas phase
12 H + CL −→ HCL
0
Gas phase
No. Changed surface (ice) reactions
EA , K
Reference
13 CO + O −→ CO2
290
Roser et al. (2001)
14 O2 + H −→ O2 H
600
Du et al. (2012)15 H + H2 CO −→ CH3 O
2100
Woon (2002)
16 O3 + H −→ O2 + OH
0
Mokrane et al. (2009)a In addition to the four reactions from Vasyunin & Herbst (2013b). Reaction rate coeﬃcient k = α(T /300)β exp(−γ/T )b Data adopted from CH O + CH reaction
33
c Estimate
1.4E-4

CB 17 S

1.2E-4

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1.4E-4

CB 17 L

1.2E-4H2O
1.0E-4H2O
1.0E-4COCO2

8.0E-5NH3
N2

6.0E-5CO
CO2

8.0E-5NH3
N2

6.0E-5

4.0E-5

4.0E-52.0E-52.0E-5t, Myr

0.0E+0
1.0

1.2

1.4

1.6

1.8

2.0

1.2E-4

1.0

CB 26

1.0E-4CONH3

4.0E-5

1.6

1.8

2.0

2.2

CB 27
H2O
CO
CO2
NH3

86.0E-5

N2

1.4

1.2E-48.0E-5CO2

6.0E-51.2

1.0E-4H2O

8.0E-5t, Myr

0.0E+02.2

N2

4.0E-52.0E-52.0E-5t, Myr

0.0E+0
1.0

1.2

1.4

1.6
1.8
1.4E-42.0t, Myr

0.0E+0

2.2

1.0

1.2

1.4

1.6

1.8

2.0

2.2

B 68

1.2E-4H2O
1.0E-4COCO2

8.0E-5NH3
N2

6.0E-5
4.0E-52.0E-5t, Myr

0.0E+0
1.0

1.2

1.4

1.6

1.8

2.0

2.2

Fig. 3.— Calculated abundances, relative to H atom number density, of major species in ice for the fivemodeled cores.

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arXiv:1504.05980v1 [astro-ph.SR] 22 Apr 2015

17. “A Ring of C2H in the Molecular Disk Orbiting TW Hya” !
A RingQi,
of C
the Molecular
Disk OrbitingTW
Hya Thierry Forveille,!
2 H inGorti,
Joel H. Kastner, Chunhua
Uma
Pierre Hily-Blant,
Karin
Oberg,
1
Sean Andrews, David
Wilner!
Joel H. Kastner, Chunhua Qi2 , Uma Gorti3 , Pierre Hily-Blant4,5 , Karin Oberg2 , Thierry
Forveille4 , Sean Andrews2 , David Wilner2!
Accepted by ApJ! http://arxiv.org/pdf/1504.05980!
ABSTRACT
We have used the Submillimeter Array to image, at ⇠1.500 resolution, C2 H
N = 3 ! 2 emission from the circumstellar disk orbiting the nearby (D = 54 pc),
⇠8 Myr-old, ⇠0.8 M classical T Tauri star TW Hya. The SMA imaging reveals
that the C2 H emission exhibits a ring-like morphology. Based on a model inwhich the C2 H column density follows a truncated radial power-law distribution,
we find that the inner edge of the ring lies at ⇠45 AU, and that the ring extends
to at least ⇠120 AU. Comparison with previous (single-dish) observations of
C2 H N = 4 ! 3 emission indicates that the C2 H molecules are subthermally>
excited and, hence, that the emission arises from the relatively warm (T ⇠ 40 K),
7
3
tenuous (n << 10 cm ) upper atmosphere of the disk. Based on these results
and comparisons of the SMA C2 H map with previous submm and scattered-light
imaging, we propose that the C2 H emission most likely traces particularly efficientphoto-destruction of small grains and/or photodesorption and photodissociationof hydrocarbons derived from grain ice mantles in the surface layers of the outerdisk. The presence of a C2 H ring in the TW Hya disk hence likely serves asa marker of dust grain processing and radial and vertical grain size segregation
within the disk.
1
Chester F. Carlson Center for Imaging Science, School of Physics & Astronomy, and Laboratory for
Multiwavelength Astrophysics, Rochester Institute of Technology, 54 Lomb Memorial Drive, Rochester NY
14623 USA (jhk@cis.rit.edu)

・SMAでTW HyaをC2H(N=3-2)で観測した!
2

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

・C2Hで45AU-120AUのリング受かった!
SETI Institute, 189 Bernardo Ave., Mountain View, CA 94043, USA; NASA Ames Research Center,3

Mo↵ett Field, CA 94035, USA

ー45auというのはCO snow line(30au)とsubmm-sizedのダストが急激に弱くなる60auの中間である!

4
Université Grenoble Alpes, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG), F-38000,
Grenoble, France; CNRS, IPAG, F-38000, Grenoble, France
5

Institut Universitaire de France, F-38000, Grenoble, France

・過去のC2H(4-3)の単一境の観測と比較しC2Hはsubthermally excitedである!
・相対的に温度が高く(T>40)希薄である(n<<10^7 cm^-3)!

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・C2Hは小さなダストの光破壊(photo-destruction)が部分的に起きているところ!
かつ/または炭水化物(hydrocarbon)の光脱離(photodesorption)と光乖離(photodissociation)!
をトレースしていると考えられる!

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・C2Hのリングの存在はダストの過程(processing)や、垂直方向や動径方向のチリのサイズの分離のマーカーとして見ることが出来る!

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Fig. 1.— Upper two rows of panels: spectral line maps of the TW Hya disk in 266 GHz
continuum (left) and C2 H (3–2) hyperfine lines (center and right) synthesized from dataobtained in merged compact+extended (C+E; top panels) and extended (E; middle panels)
SMA antenna configurations. In each panel, the shaded oval indicates the FWHM andorientation of the synthesized beams, and the cross represents the position of TW Hya(J2000 coordinates ↵ = 11:01:51.834, = 34:42:17.149). Contours levels are 50%, 75% and
90% of the peak in each image. For the C+E (E) configurations, these peak fluxes are: 570(401) mJy beam 1 for the 266 GHz continuum map, 1.33 (0.49) Jy km s 1 beam 1 for the34,4 23,3 transition map, and 1.18 (0.41) Jy km s 1 beam 1 for the 34,3 23,2 transition
map, with noise levels of 5 (8) and 0.04 (0.08) for the continuum and line maps, respectively.
Bottom panel: spectrum of C2 H (3–2) hyperfine lines in the 262.005 GHz spectral region.

Fig. 4.— Distribution of C2 H for the best-fit model, overlaid as grey shading on contour
plots of disk density (left, in cm 3 ) and gas kinetic temperature (right, in K).

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arXiv:1501.05659v2 [astro-ph.EP] 21 Apr 2015

Scott J. Kenyon
Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138
e-mail:skenyon@cfa.harvard.edu

18. “Formation of Super-Earth Mass Planetsat 125–250 AU from a Solar-type Star”!
Benjamin C. Bromley
Scott J. Kenyon and Benjamin C. Bromley!
of Physics, Journal!
University of Utah, 201 JFB, Salt Lake City, UT 84112!
Accepted Department
by Astrophysical!
http://arxiv.org/pdf/1501.05659!
e-mail: bromley@physics.utah.edu

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ABSTRACT
We investigate pathways for the formation of icy super-Earth mass planets
orbiting at 125–250 AU around a 1 M⊙ star. An extensive suite of coagulation
calculations demonstrates that swarms of 1 cm to 10 m planetesimals can form
super-Earth mass planets on time scales of 1–3 Gyr. Collisional damping of
10−2 −102 cm particles during oligarchic growth is a highlight of these simulations.
In some situations, damping initiates a second runaway growth phase where
1000–3000 km protoplanets grow to super-Earth sizes. Our results establish theinitial conditions and physical processes required for in situ formation of superEarth planets at large distances from the host star. For nearby dusty disks in
HD 107146, HD 202628, and HD 207129, ongoing super-Earth formation at 80–
150 AU could produce gaps and other structures in the debris. In the solar
system, forming a putative planet X at a ! 300 AU (a " 1000 AU) requires amodest (very massive) protosolar nebula.
Subject headings: planetary systems – planets and satellites: formation – solar
system: formation

1. INTRODUCTION
・1Msun周りの125au-250auの軌道で氷のスーパーアースの形成経路を調べる!
For nearly a century, planet X has haunted the outer Solar System. Originallyenvisioned
・凝固の計算の広いsuiteは、1cm-10mの微惑星群がsuper-earth
massの惑星を1-3Gyrで形
as a way to explain irregularities in the orbits of Uranus and Neptune (e.g., Lowell 1915;

成できることを示した。!
Bower 1931; Brouwer 1955; Rawlins 1970, 1972; Harrington 1988), planet X – along with the!

variants Nemesis and Tyche – has since been invoked to explain the orbital properties of somecomets and trans-Neptunian objects (e.g., Matese et al. 1999; Gomes et al. 2006; Lykawka

・寡専成長期の10^-2 ..10^2 cmの粒子の衝突減衰が、これらシミュレーションの重要な点
である。!

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・いくつかの状況で、減衰は、1000-3000km原始惑星からsuper-earth
sizeへの第二期急– 49 –
速成長段階を始める!

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・我々の結果は、中心星から大きくはなれた場所でsuper-earth惑星が形成した本来の位置
を、初期状態と物理過程を確立した!

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Fig. 4.— Maximum planet radius at a = 125 AU as a function of r0 and q for b = 9/8.
To improve clarity, points are slightly oﬀset from the nominal r0 . The horizontal grey bar
indicates the radius of an Earth-mass planet with ρs = 1.5 g cm−3 . Calculations with r0 =1 cm to 1 km and q ! 4.5 produce super-Earth mass planets.

Fig. 6.— Comparison of cumulative (lower panel) and relative cumulative (upper panel) size
distributions for three idealized power law size distributions. To construct the relative size
distribution, we adopt a normalization with qs = 2.7 which yields nc,rel ≡ 1 at r = 1 cm.
Black curves: nl = 1, qs = 2.7, qi = 1.0, ql = 3.5, r1 = 0.1 km, r2 = 10 km. Cyan curves: nl= 1, qs = 2.8, qi = 1.2, ql = 4.0, r1 = 0.03 km, r2 = 30 km. Magenta curves: nl = 1, qs =2.6, qi = 1.7, ql = 4.0. r1 = 0.3 km, r2 = 100 km. Relative size distributions allow an easierassessment of the diﬀerences between power-law components.

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Draft version May 6, 2015
Preprint typeset using LATEX style emulateapj v. 5/2/11

19. “Evidence for Decay of Turbulence by MHD Shocks in Molecular Clouds via CO
EVIDENCE FOR DECAY OF TURBULENCE BY MHD SHOCKS IN MOLECULAR CLOUDS VIA CO
Emission”!
EMISSION
Rebecca L. Larson, Neal J. Evans
II, Joel D. 1Green, and Yao-Lun
Yang!
1
Rebecca L. Larson , Neal J. Evans II , Joel D. Green 1,2 , & Yao-Lun Yang 1!
Accepted by The Astrophysical Journal! http://arxiv.org/pdf/1505.00847!

arXiv:1505.00847v1 [astro-ph.GA] 4 May 2015

Draft version May 6, 2015

ABSTRACTWe utilize observations of sub-millimeter rotational transitions of CO from a Herschel Cycle 2
open time program (“COPS”, PI: J. Green) to identify previously predicted turbulent dissipation bymagnetohydrodynamic (MHD) shocks in molecular clouds. We find evidence of the shocks expected
for dissipation of MHD turbulence in material not associated with any protostar. Two models fit
about equally well: model 1 has a density of 103 cm−3 , a shock velocity of 3 km s−1 , and a magnetic
field strength of 4 µG; model 2 has a density of 103.5 cm−3 , a shock velocity of 2 km s−1 , and amagnetic field strength of 8 µG. Timescales for decay of turbulence in this region are comparable
to crossing times. Transitions of CO up to J of 8, observed close to active sites of star formation,
but not within outflows, can trace turbulent dissipation of shocks stirred by formation processes.
Although the transitions are diﬃcult to detect at individual positions, our Herschel-SPIRE survey of
protostars provides a grid of spatially-distributed spectra within molecular clouds. We averaged all
spatial positions away from known outflows near seven protostars. We find significant agreement withpredictions of models of turbulent dissipation in slightly denser (103.5 cm−3 ) material with a stronger
magnetic field (24 µG) than in the general molecular cloud.

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widely accepted, but direct evidence for the shocks inopaque molecular clouds has proven elusive. The disThe dust in molecular clouds shields the interior fromcovery of such evidence would resolve a long-standing
ultraviolet
radiation, lowering the kinetic temperature to・分子雲内でMHDショックによって乱流が散逸する以前から予測を確認する為に!
question.
about 10 K. For this temperature, the isothermal soundThe sources of this turbulence are still somewhat un−1
speed isonly about 0.2 km s . In contrast, the observed
HearschelのCO回転遷移の観測を利用した!
clear.
One source for renewing the turbulence is outlinewidths of molecular transitions indicate much larger
flows from forming stars. The outflows are hypersonic,
velocity
dispersions.
When
these
facts
first
becameevi・原始星が付随しないところでMHD乱流による散逸で予測されるショックの証拠を発見!
but they may couple energy to the surrounding gas via
dent, Goldreich & Kwan (1974) suggested that the large
magnetic disturbances. Thus, we may find evidence forlinewidths
werecausedbyoverallcollapseofthemolec・この領域で乱流の散逸のタイムスケールは横断時間と近い!
enhanced dissipation in the surroundings of outflows, butular cloud, rejecting the alternative of turbulent motions
we must avoid the outflows to avoid confusion.
・かなり密度が高い(10^3.5
cm^-3)の物質で一般的な分子雲よりも強い磁場(24uG)!
because such motions should decay on a timescale similar
Much of the energy deposited in the gas by shocks is
to a crossing time. Zuckerman & Palmer (1974) noted
radiatedaway, and a likely route is through CO and H2での乱流散逸のモデル予想と良く一致した。!
that allowing all molecular clouds to collapse at freerotationaltransitions, as well as through enhanced emisfall would produce a star formation rate far higher thansion by atoms and ions, such as OI and CII. Attempts to
that
of
the
Milky
Way.
Zuckerman&
Evans(1974)sug), and that the timescale for tursignatures of turbulent dissipation in lines of H2 , CII,
TABLE find1
that
the linewidths
were indeed caused by turabout a gested
factor of
3 shorterthanand OI are frustrated by the fact that these lines could
Source List
bulence,andthatmagnetic
fields
could
slow
the
dis(Pon et al. 2015b). This is an imalso be excited by low intensity photodissociation regions
the motions
The idea
it appliessipation
only to ifa single
region were sub-Alfvénic.
SourceCloud Dist (PDRs)
RA (J2000)
Dec the surface of all clouds (Li et al.
which cover
linewidths
nation of thatdatathefrom
diﬀerent arein- indicative of turbulent motions
2002).
A
renewedopportunity to detect the signature
L1455-IRS3
widespread(Myers1999; SolomonPer
et al.250 03h28m00.4s +30d08m01.3s
ation with isothertechniques
in dif-& Gammie
oftheshockshas
arisenIRAS
03301+3111Per250
03h33m12.8s+31d21m24.2s
1987;
Larson1981),dissibut simulations(Stone et al.Tau
1998;140 04h31m34.1s +18d08m04.9sdue to the combination of new
dd confidence
thatturbulent
L1551-IRS5
focusing on the mid-J CO lines and the ability
Smith
et al. results2000) indicatethattheshould140 models,n detected.
Similarhave
TMR
1 turbulence Tau
04h39m13.9s+25d53m20.6softhe Herschel
instruments (both HIFI and SPIRE) to
decay
via
shocks.
Evenwhenmagnetic
fields
are
inTMC
1A
Tau
140
04h39m35.0s+25d41m45.5s
d for apparently starless clumps
detectthese
lines
toward regions that are not directly
TMC
1
Tau
140
04h41m12.7s+25d46m35.9s
cluded, simulations indicate that turbulence decays,
et al. (2015a).
by outflows.
L1157 (MHD) or C-shocksCore
325 aﬀected
20h39m06.3s+68d02m16.0s
but
throughmagnetohydrodynamic
resent a sample of SPIRE specIsolated MC
Tau
140 04h39m53.0s+25d45m00.0s
Models fromPon et al. (2012) indicate that turbulent(Mullan1971; Draine
1980; Draine & McKee 1993), or
olecular clouds
including
one nearshocksenhance
mid-Jcloud
CO emission over that from quiNote.
—
List
of
protostellar
sourcesandtheisolated
molecular
through Using
coherent,
small-scalevortices (Godard et al.
n near protostars.
portions
position used in this sample, sorted by escent
RA. Distances
measuredin
PDR aremodels(Kaufmanet al. 1999). Observa2014).
Strongevidence
for
decay
has
been
found
parsecs.
ted by outflows or nearby prototional
evidencefor
turbulentdissipation
has been foundin diﬀuse
translucent
clouds using chemical inwe examine
them
forandevidence
of
!
in
the
PerseusB1-East5
regionbyPon
et al. (2014).
et al.
andseparate
H2 emission
lines set by pixel, including theeach data
dicated bydicators
increased(Godard
luminosity
in 2014) We
Theyregion of the Perseus molecular cloud(Falgarone et al. 2005). The object
latter method
hasthealsoarea
in- arounditself andit.chose
The this
continuum
as oneno significant heating sources other thandicated evidence for decay on the outskirts of the Tauusingwith
an automatedver the contribution from PDRs for in each pixel was first calculated
shocks,cosmicrus molecular cloud (Goldsmith et al. 2010). The idea
Data Languagerays,(IDL)and interstellar radiation fields
Object5 → 4 Selection
and higher (Pon et al. 2012). routine written in Interactive (ISRF);
there spectrum
are no signs of embedded young stelthat turbulence decays in denser
is also from the original
andmolecular
was thenclouds
subtracted
lar objects.
Measurementsof the CO J = 5 → 4 andere analyzed were taken from theto create a flat (continuum-subtracted)
spectrum.
The
J
=
6
→
5
transitions
show
valuesenhanced over PDR
Universityof low
Texasluat Austin,
DepartmentofAstronomy,(Green et al. 1in
prep.) offlat spectra from each pixel in the combination were
Austin,TXmodelsbyKaufmanetal.
(1999).
Pon
et al. (2014) conotostars. Theseobservations wereaveraged
togethersignal-to-noise ratio.
2 Space Telescope Science Institute,
Baltimore,
MD to improve thecludedthatthefillingfactorofshockstoward this poproject as they tend
to have powerThe CO lines in each average were fitted by a Gaussian
duce emission in very high-J lines.
function which yields the intensity integrated over theselected objects with weaker outline. This intensity was converted to the units used in
ws well confined to certain regions,the models (erg s−1 cm−2 arcsec−2 ). Upper limits fors away from the outflows. In adthe non-detections were calculated by taking the noise
ne region within a filament of thelevel and multiplying by 3 to get the 3σ value. The CO
not include any embedded source,
J = 7 → 6 line flux estimate is particularly uncertain asple of the molecular cloud without
it is blended with the [C I] line which is very prominent
We refer to this observation as thein the isolated molecular cloud field. Figure 1 shows
ページ 9/10
ud.
an example of the blended CO J = 7 → 6 and [C I]33
he seven regions with embedded
P2Fig.
→ 4.—
P1 Grandlines andan ofoverlay
the double-Gaussian
averageall sevenofobjects:
Observed CO emiscted for this study. L1455-IRS3,
lines
from
CO J =to8 →7 (left) to CO= 4 → from3 (right)
fromfitsionthatwasapplieddistinguish
theJfluxes
eachtheindividually.
center (light blue), outflow (purple), and non-outflow (green)d TMR1 were chosen becauseline
pixels plotted over the model they best fit to: highest density

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1. INTRODUCTION

tation axes

njamin T. Lewis1,2? , Matthew R. Bate1,2 , and Daniel J. Price2

ool of Physics and Astronomy, University of Exeter, Stocker Road, Exeter EX4 4QL“Smoothedparticlemagnetohydrodynamic
simulationsof protostellar
outflows withnash Centre for 20.
Astrophysics,
School of
Mathematical
Sciences, Monash University,
Clayton, Vic 3800,
Australia

mis- aligned magnetic field and rotation axes” !
Benjamin T. Lewis, Matthew R. Bate, and Daniel J. Price!
ted 2015 April 28. Received 2015 April 23; in original form 2015 March 06.
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Accepted by MNRAS!
http://arxiv.org/pdf/1504.08322v1!

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ABSTRACT

We have developed a modified form of the equations of smoothed particle magnetohydrodynamics which are stable in the presence of very steep density gradients. Using
this formalism, we have performed simulations of the collapse of magnetised molecular cloud cores to form protostars and drive outflows. Our stable formalism allows forsmaller sink particles (< 5 AU) than used previously and the investigation of the e↵ectof varying the angle, #, between the initial field axis and the rotation axis. The natureof the outflows depends strongly on this angle: jet-like outflows are not produced at allwhen # > 30°, and a collimated outflow is not sustained when # > 10°. No substantial
outflows of any kind are produced when # > 60°. This may place constraints on thegeometry of the magnetic field in molecular clouds where bipolar outflows are seen.
Key words: accretion, accretion discs – MHD – stars: formation – stars: winds,
outflows.

・急激な密度の勾配があるときに安定な
smoothed
particlemagnetohydrodynamics
NTRODUCTION
pendent on
the angle (which
we denotewith #) between thefield and rotation axis.
netic fields are (SPMHD)を改良した方程式を作った!
one of the most important forces influSmoothed particle hydrodynamics (SPH) methods haveg the formation of protostars and may resolve several
been applied to many problems related to the formation ofions about the formation of stars that are left unanstars, beginning with the original work of Lucy (1977). Thesed by purely hydrodynamic
theories. That the molecu- (原始星形成、アウトフロー駆動)をシミュレーションした!
・磁場がある分子雲ガスの収縮
hydrodynamic methods have been extended to magnetohyouds that ultimately produce protostars are magnetised
drodynamics(MHD), originally by Gingold & Monaghan
l known (Crutcher
et al. 1993; Crutcher 2012), and this・新しい方程式は、以前よりも小さなsink
particleが可能で、初期の場の軸と回転軸の間(1977) and Phillips & Monaghan (1985), with limited suce confirmed with observations of Herbig-Haro objects
cess. Hitherto, such work has been limited by various nuの変化角θの効果を調べることが出来る。!
distinctive bipolar
outflows, which must have a magmerical instabilities, ranging from unphysical pairing (theorigin. Additionally, these outflows may help explain‘tensile instability’) of SPH particles (Swegle et al. 1995;i↵erence between the angular momentum observed in
Børve et al. 2001) to the production of equally unphysicalcular cloud coresand that of the resultant stars. This・アウトフローはこの角度に強く依存する；jetのようなアウトフローはθ>30degの時にはnon-solenoidal fields (Tricco & Price 2012). The most recent
wever, dependent on the ability of the protostar to proinstability, and the one that this paper tackles is that a for作られない、そしてcollimateda strong outflow– if at certain angles this is impossible outflowはθ>10degで維持されない。θ>60degでアウトフ
malism of smoothed particle hydrodynamics incorporating
may place constraints on the initial field geometry. Reローは作られない。!
fixes to all of the above deficiencies (Price 2012) is unstableadvances in observational
technology have shown thatwhen ‘small’ sink particles (Bate et al. 1995) are used.
magnetic field structure can be quite complex (Stephens2014) and that the hitherto common assumption that
Most recently, Price et al. (2012) examined the collapse
・これはbipolar
outflowが見えている場所での分子雲での磁場の方向に制約を課すことがoutflow, and rotation
axis are all aligned
may be inof a magnetised molecular cloud core all the way to the forct 10(Hull etB.
al. T.
2013).
On very
scales Donati
et al.
mation of the first hydrostatic core (Larson 1969) and Bate
できると思われる。!
Lewis,
M.smallR. Bate,and D.
J. Price) have observed a 20° misalignment between the rotaet al. (2014) have continued to the stellar core. To model theand field axes of AA Tau. Previous work, e.g. Ciardi
evolution significantly beyond protostar formation, sink par6
T = 25420
yrs using AMRT codes= 26400has
yrs shown that theθ=010nnebelle(2010),
ticles are a necessary evil
since modelling bothθ =themagnee and extent of the protostellar outflow is strongly detohydrodynamics of the protostar and also the surrounding

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-14

mail: blewis@astro.ex.ac.uk

15 RAST = 26890 yrs

T = 27380 yrs

cloud is computationally unfeasible due to the widely different length and time scales involved. Consequently, some
way of stabilising the equations of smoothed particle mag-5.5-16

θ = 45

θ = 90Figure 10. Density cross-sections for # = 20°. The e↵ect of thecomplicated field geometry in expelling material from around theprotostar, andページ
thus distrupting
10/10 the collimated jet, can be clearly
seen.

5

4.5

-18
300 AUlog |v| [cm/s]

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log density [g/cm3]!

300 AU

Figure 11. Cross-sections of |v| at T = 27870 yrs (i.e. late enoughthat the magnetic e↵ects seen in fig. 8 will have been able to disrupt the outflow). The two upper plots show the strongly collimated outflows seen for low values of # whilst the # = 45 and90° plots show the more complicated, di↵use outflows which at
steeper angles essentially cease altogether.