• Star formation Newsletter #304 9-18 担当:佐藤一樹
9. Planetesimal formation during protoplanetary disk buildup
10. Extreme star formation in the Milky Way: Luminosity
distributions of young stellar objects in W49A and W51
11. Gas expulsion in highly substructured embedded starclusters
12. On the Formation of Runaway Stars BN and x in the Orion
Nebula Cluster
13. Bipolar Jets Launched by a Mean-field Accretion Disk
Dynamo14. Turbulence in the TW Hya disk
15. Tracing the atomic nitrogen abundance in star-forming
regions with ammonia deuteration
16. Depletion of heavy nitrogen in the cold gas of star-forming
regions
17. S Coronae Australis – a T Tauri Twin
18. Velocity-Resolved [CII] Emission from Cold Diffuse Clouds
in the Interstellar Medium10. Extreme star formation in the Milky Way: Luminosity
distributions of young stellar objects in W49A and W51
D. J. Eden, T. J. T. Moore, J.S. Urquhart, D. Elia, R. Plume, C. König, A. Baldeschi, E.
Schisano, A.J. Rigby, L.K. Morgan, M.A. Thompson
http://arxiv.org/pdf/1803.00475

概要：
星形成領域W49A, W51 での星形成の特徴の違いを調べた
Clumpの質量分布はconsistentだった
YSOの光度分布は異なっていた
W49 A の中心部では、系外銀河で見られるようなstarburst
観測：
Hi-GAL(70,160,250,350,500μm, 6”-35”)
JCMT(850μm, 14.4”)
13CO(J=1-0, J=3-2) もJCMT, GRS などで
W49 Aで173, W51で293のcompact
sourceを同定

W49A(上)とW51(下)Flux map

Mass- Luminocityは特に違いはない(左)CMD:クランプ数/Mass(右) LD: クランプ数/Luminosity
Luminosity 分布に違いがみられる
W51は銀河系内で平均的な値
W49Aは傾きが弱い⇒W49 Aは中心部で際立った星形成

W49 A は高エネルギーγ線も観測されている(Brun et al. 2011)⇒W49 A 中心部 は系外銀河のstarburst と似ている(mini-starburst?)

12. On the Formation of Runaway Stars BN and x in
the Orion Nebula Cluster
Juan P. Farias and Jonathan C. Tan
https://arxiv.org/pdf/1712.08485
Orion BN は Orion 星雲と30km/s の速度差
この速度差の原因には議論がある

3天体の移動のイメージ

シナリオ例
・Orion BN が軌道から外れた (Tan 2004)
・Source I (近傍のprotostar)がBNと同時に反対方向へ (Bally & Zinnecker, 2005)
・近年、新たにsource x がHSTで発見され、source xの質量が~3M⦿と見積もられた(Luhman et al. 2017)⇒source x, BN, source I (I1とI2のbinary)の4天体のinteractionとしてこの系を数値的に計算した

BN

Source I

Source x

Binary 同士のinteractionを考える

Source Iの質量>7Mとしたほうが観測によく合う

Source x を考えたとき(赤)Source x を考えないとき(青)横軸のSource I の質量が青のとき20M⦿,一方赤のとき7M⦿で済む※BNの質量は8-12M⦿
Source I の質量を正確に測定することで、どちらのシナリオが正しいか確かめられる15. Tracing the atomic nitrogen abundance in starforming regions with ammonia deuteration
Kenji Furuya and Magnus V. Persson
https://arxiv.org/pdf/1802.08494.pdf
概要：
星形成領域でN原子がどう(NI?N2?NH3?)存在しているかを知りたい→[ND2H/NH2D]/[NH2D/NH3]を測定することで推測が可能→ALMA, VLAなどで観測可能な帯域、観測時間的にもOK気相のNIやN2を直接観測することはできない
CN/HCNを用いた測定法もあるが、N2に不定性Dを含むほうが早く反応することを利用する
重水素を含むアンモニアから推定する[ND2H/NH2D]/[NH2D/NH3]をつかうことでD/Hによらない検証ができる

原始星誕生時から9.3×104yr後のenvelopeのAbundance シミュレーション結果
破線は固相(a)(b)(c) 3種のモデルでのNの状態分布(d) 全アンモニアのうち氷になったものの比率
段階により[ND2H/NH2D]/[NH2D/NH3]比が異なる→モデルと突き合わせNの状態分布を推定することが可能
・VLAやALMAのバンド7などでNH3,NH2D,NHD2を同時観測可能
・この手法はH

16．DEPLETION OF HEAVY NITROGEN IN THE COLDGAS OF STAR-FORMING REGIONS
Kenji Furuya and Yuri Aikawa
https://arxiv.org/pdf/1803.06787.pdf

9. Planetesimal formation during protoplanetary diskbuildup
J. Dr，a˙zkowska1 and C.P. Dullemond2

Models of dust coagulation and subsequent planetesimal formation are usually computed on the backdrop of analready
fully formed protoplanetary disk model. At the same time, observational studies suggest that planetesimalformation
should start early, possibly even before the protoplanetary disk is fully formed. In this paper, we investigate underwhich conditions planetesimals already form during the disk buildup stage, in which gas and dust fall onto the disk
from its parent molecular cloud. We couple our earlier planetesimal formation model at the water snow line to asimple model of disk formation and evolution. We find that under most conditions planetesimals only form after thebuildup stage when the disk becomes less massive and less hot. However, there are parameters for whichplanetesimals
already form during the disk buildup. This occurs when the viscosity driving the disk evolution is intermediate(αv ∼ 10−3–10−2) while the turbulent mixing of the dust is reduced compared to that (αt <∼10−4), and with theassumption that water vapor is vertically well-mixed with the gas. Such αt ≪ αv scenario could be expected
forlayered accretion, where the gas flow is mostly driven by the active surface layers, while the midplane layers,
wheremost of the dust resides, are quiescent.
http://arxiv.org/pdf/1803.00575

11. Planetesimal formation during protoplanetary diskbuildupGas expulsion in highly substructured embedded
star clusters
J. P. Farias1, M. Fellhauer2, R. Smith3, R. Dom´ınguez2 and J. Dabringhausen4

We investigate the response of initially substructured, young, embedded star clusters to instantaneous gas expulsionof their natal gas. We introduce primordial substructure to the stars and the gas by simplistically modelling the starformation process so as to obtain a variety of substructure distributed within our modelled star forming regions. We
show that, by measuring the virial ratio of the stars alone (disregarding the gas completely), we can estimate how
muchmass a star cluster will retain after gas expulsion to within 10% accuracy, no matter how complex the backgroundstructure of the gas is, and we present a simple analytical recipe describing this behaviour. We show that theevolutionof the star cluster while still embedded in the natal gas, and the behavior of the gas before being expelled, are crucial
processes that affect the timescale on which the cluster can evolve into a virialized spherical system. Embedded starclusters that have high levels of substructure are subvirial for longer times, enabling them to survive gas expulsion
better than a virialized and spherical system. By using a more realistic treatment for the background gas than ourprevious studies, we find it very difficult to destroy the young clusters with instantaneous gas expulsion. We conclude
that gas removal may not be the main culprit for the dissolution of young star clusters.
https://arxiv.org/pdf/1803.00581

13. Bipolar Jets Launched by a Mean-field Accretion Disk
DynamoChristian Fendt1 and Dennis Gamann1
By applying magnetohydrodynamic simulations, we investigate the launching of jets driven by a disk magnetic field
generated by a mean-field disk dynamo. Extending our earlier studies, we explore the bipolar evolution of the disk
α2-dynamo and the outflow. We confirm that a negative dynamo-α leads to a dipolar magnetic field geometry,
whereas positive values generate quadrupolar fields. The latter remain mainly confined to the disk and cannot launchoutflows. We investigate a parameter range for the dynamo-α ranging from a critical value below which field
generationis negligible, α0,crit = −0.0005, to α0 = 1.0. For weak |α0| ≤ 0.07, two magnetic loop structures with opposite
polarity
may arise, which leads to reconnection in the disk and disturbs the field evolution and the accretion-ejection process.
For a strong dynamo-α, a higher poloidal magnetic energy is reached, roughly scaling with Emag ∼ |α 7,etα, α14. Turbulence in the TW Hya disk
Kevin Flaherty1, A. Meredith Hughes1, Richard Teague2, Jacob B. Simon3,4, Sean M. Andrews5 andDavid J. Wilner5
Turbulence is a fundamental parameter in models of grain growth during the early stages of planet formation. As
such, observational constraints on its magnitude are crucial. Here we self-consistently analyze ALMA CO(2-1), SMACO(3-2), and SMA CO(6-5) observations of the disk around TW Hya and find an upper limit on the turbulent
broadening of <0.08cs (α <0.007 for α defined only within 2-3 pressure scale heights above the midplane), lower than
the tentative detection previously found from an analysis of the CO(2-1) data. We examine in detail the challengesof image plane fitting vs directly fitting the visibilities, while also considering the role of the vertical temperature
gradient, systematic uncertainty in the amplitude calibration, and assumptions about the CO abundance, as potential
sources of the discrepancy in the turbulence measurements. These tests result in variations of the turbulence limit
between <0.04cs and <0.13cs, consistently lower than the 0.2-0.4cs found previously. Having ruled out numerous
factors, we restrict the source of the discrepancy to our assumed coupling between temperature and density throughhydrostatic equilibrium in the presence of a vertical temperature gradient and/or the confinement of CO to a thinmolecular layer above the midplane, although further work is needed to quantify the influence of these prescriptions.
Assumptions about hydrostatic equilibrium and the CO distribution are physically motivated, and may have a small
influence on measuring the kinematics of the gas, but they become important when constraining small effects suchas the strength of the turbulence within a protoplanetary disk.
https://arxiv.org/pdf/1803.03842

17. S Coronae Australis – a T Tauri Twin
ChG¨osta F. Gahm1, Peter P. Petrov2, Larisa V. Tamovtseva3, Vladimir P. Grinin3,4, Eric C. Stempels5,and Frederick M. Walter6
The star S CrA is a tight visual binary consisting of two classical T Tauri stars, both with outstanding spectral
characteristics and brightness variations. High-resolution spectra were collected at ESO and photometricobservations
with the SMARTS telescope. Both stars undergo large variation in brightness caused mainly by variable foregroundextinction.
From the stellar parameters we conclude that the two stars are remarkably similar, and that S CrA can be regarded
as a T Tauri twin. Rotational periods and inclinations are also similar. The stars differ, however, in terms of degreeof veiling and emission line profiles.
We compared observed Balmer emission line profiles with models including magnetospheric accretion and a diskwind.
We found a good match between observed signatures of accreting gas, wind features, and rotational velocities withthose resulting from our modelling for inclinations of ∼ 65 degrees. At this orientation the trajectories of infalling
gas just above the stellar surfaces are parallel to the line-of-sight, and accordingly we observe extended red-shifted
absorption components extending to + 380 km/s, the estimated free-fall velocity at the surface. However, our soderived inclinations differ from those derived from interferometric near-infrared spectroscopy, and we discusspossiblecauses for this puzzling discrepancy.

http://arxiv.org/pdf/1804.04971

18. Velocity-Resolved [CII] Emission from Cold Diffuse
Clouds in the Interstellar Medium
P.F. Goldsmith1, J.L Pineda1, D.A. Neufeld2, M.G. Wolfire3, C. Risacher4 and R. Simon5

We have combined emission from the 158 μm fine structure transition of C+ observed with the GREAT and upGREAT
instruments on SOFIA with 21–cm absorption spectra and visual extinction to characterize the diffuse interstellar
clouds found along the lines of sight. The weak [Cii] emission is consistent in velocity and line width with thestrongest
HI component produced by the Cold Neutral Medium (CNM). The HI column density and kinetic temperature are
known from the 21cm data, and assuming a fractional abundance of ionized carbon, we calculate the volume density
and thermal pressure of each source, which vary considerably, with 27 cm−3 ≤ n(H0) ≤ 210 cm−3 considering only
the atomic hydrogen along the lines of sight to be responsible for the C+, while 13 cm−3 ≤ n(H0 + H2) ≤ 190 cm−3
including the hydrogen in both forms. The thermal pressure varies widely with 1970 cm−3K ≤ Pth/k ≤ 10440 cm−3Kfor H0 alone and 750 cm−3K ≤ Pth/k ≤ 9360 cm−3K including both H0 and H2. The molecular hydrogen fraction
varies between 0.10 and 0.67. Photoelectric heating is the dominant heating source, supplemented by a moderately–enhanced cosmic ray ionization rate, constrained by the relatively low 45 K to 73 K gas temperatures of the clouds.
The resulting thermal balance for the two lower–density clouds is satisfactory, but