Star Formation Newsletter No. 346, 24-28
植田 高啓 (国立天文台)

24. Stellar Rotation of T Tauri stars in the Orion Star-Forming Complex
25. A Revised Description of the Cosmic Ray-Induced Desorption of InterstellarIces
26. VLA Observations of 9 Extended Green Objects in the Milky Way: Ubiquitous
Weak, Compact Continuum Emission, and Multi-Epoch Emission from
CH3OH, H2O, and NH3 Masers
27. Probing the chemical complexity of amines in the ISM: detection ofvinylamine (C2H3NH2) and tentative detection of ethylamine (C2H5NH2)
28. On the Three-Dimensional Structure of Local Molecular Clouds

https://arxiv.org/abs/2110.06431

24. Stellar Rotation of T Tauri stars in the Orion Star-Forming Complex

Javier Serna, Jesús Hernández, Marina Kounkel, Ezequiel Manzo-Martínez, Alexandre Roman-Lopes,
Carlos G. Román-Zuñiga, Maria Gracia Batista, Giovanni Pinzón, Nuria Calvet, Cesar Briceño,
Mauricio Tapia, Genaro Suárez, Karla Peña Ramirez, Keivan G. Stassun, Kevin Covey, Jaime VargasGonzález, José Gregorio Fernández-Trincado
We present a large-scale study of stellar rotation for T Tauri stars in the Orion Star-Forming Complex.
We use the projected rotational velocity (v sin(i)) estimations reported by the APOGEE-2 collaboration
as well as individual masses and ages derived from the position of the stars in the HR diagram,considering Gaia-EDR3 parallaxes and photometry plus diverse evolutionary models. We nd anempirical trend for v sin(i) decreasing with age for low-mass stars (0.4M⊙ < M∗ < 1.2M⊙). Our
results support the existence of a mechanism linking vsin(i) to the presence of accreting protoplanetarydisks, responsible for regulating stellar rotation in timescales of about 6 Myr, which is the timescale inwhich most of the T Tauri stars lose their inner disk. Our results provide important constraints tomodels of rotation in the early phases of evolution of young stars and their disks.

• Orion Star-Forming ComplexのT-Tauri starsの自転速度をサーベイした• 得られた自転速度と、星の年齢や円盤の有無(Hα emissionの強さ)と比較すること
で星・円盤システムの中で自転速度がどのように時間進化しているか議論
主な結論：• 自転速度は~5Myr程度かけて時間と共に減少、その後はやや増加
fi -> 円盤寿命と同程度なので、星-円盤相互作用によって自転速度が決定されている

背景：• 恒星の自転速度は恒星近傍の惑星軌道に影響を与える• 恒星の自転速度は、恒星自身の膨張・収縮、恒星風による角運動量放出、円盤との相互作用（と初期の角運動量分布）などによって決まる• 多くの研究では円盤との相互作用によって自転速度が下がるとされているが、否定的な研究もある（らしい）
ターゲット Orion Star-Forming Complex :Orion Nebula Cluster (~1-2Myr)やλ Orionis cluster (~4-6Myr)など、幅広い年齢の星形成領域が存在-> 自転速度の時間進化を調べるのにちょうど良い手法：• Gaia-EDR3のkinematical dataに基づきOSFCに属するT-Tauri starを選定• Hαの強度に応じてWTTS, CWTTS, CTTSに分類（円盤があるかないか）• NIR spectraから有効温度、自転速度vsin(i)、光度などを導出（Kounkel et al. 18,19）• 得られた温度・光度からHRダイアグラムをもとに年齢を決定• （TESSのライトカーブから回転周期と、↑で得られた回転速度を比較してるが主要な結果とどう繋がっているかよくわからなかったので割愛）

観測された自転速度の時間進化と理論モデルの比較• ３つの星進化モデルから、各恒星について年齢を導出• 自転速度の時間進化モデル(Gallet & Bouvier 2015)、円盤がずっと存在するモデル
Model A、円盤が全くないModel Bと比較
どの星進化モデルでも、G&B 2015の自転速度進化モデルと整合的
最初の~5Myrは自転速度が減少-> 円盤寿命と同程度(Hernandez+07)-> 恒星磁場と円盤の相互作用により恒星角運動量が減少
5Myr以降は緩やかに増加-> 円盤がなくなり、恒星の内部構造進化(収縮に伴う回転速度の増加)と恒星風による角運動量放出の釣り合いで自転速度が決定

自転速度と円盤降着の関係性
Hαの強度から円盤降着の強さに応じてWTTS, CWTTS, CTTSに分類

highlyaccreting

円盤降着が弱いと考えられるWTTSは、円盤降着が強いCTTSと比べて高速で回転（>~30km/s）しているものが多い
最初の~1.5MyrはWTTSの方が統計的に自転速度が速いが、1.5Myr程度を過ぎると統計的な差はない(ただしサンプル数が少ない)-> 降着円盤が恒星の自転を抑制するというモデルと整合的https://arxiv.org/abs/2110.01791

27. Probing the chemical complexity of amines in the ISM: detection of vinylamine(C2H3NH2) and tentative detection of ethylamine (C2H5NH2)
Shaoshan Zeng, Izaskun Jiménez-Serra, Víctor M. Rivilla, Jesús Martín-Pintado, Lucas F. RodríguezAlmeida, Belén Tercero, Pablo de Vicente, Fernando Rico-Villas, Laura Colzi, Sergio Martín, MiguelA. Requena-Torres
Amines, in particular primary amines (R-NH2) are closely related to the primordial synthesis of aminoacids since they share the same structural backbone. However, only limited number of amines has been
identi ed in the ISM which prevents us from studying their chemistry as well as their relation to prebiotic species that could lead to the emergence of life. In this letter, we report the rst interstellar
detection of vinylamine (C2H3NH2) and tentative detection of ethylamine (C2H5NH2) towards theGalactic Centre cloud G+0.693-0.027. The derived abundance with respect to H2 is (3.3±0.4)×10−10
and (1.9±0.5)×10−10, respectively. The inferred abundance ratios of C2H3NH2 and C2H5NH2 withrespect to methylamine (CH3NH2) are ∼0.02 and ∼0.008 respectively. The derived abundance ofC2H3NH2, C2H5NH2 and several other NH2-bearing species are compared to those obtained towards
high-mass and low-mass star-forming regions. Based on recent chemical and laboratory studies,possible chemical routes for the interstellar synthesis of C2H3NH2 and C2H5NH2 are discussed. 

fifi

ISMで初めてビニルアミンC2H3NH2とエチルアミンC2H5NH2を検出したこと報告する
レター論文

背景：

• 第一級アミン（R-NH2）はグリシンを始めとするアミノ酸と構造が似ており、生命の起源という観点から重要（アミノ酸の前駆体である可能性もある）• これまでISMでグリシンは未検出だが、いくつかの第一級アミンは検出されている• 特に分子雲G+0.693-0.027ではこれまでに、NH2CN, NH2CHO, CH3NH2, NH2OH,
NH2CONH2, NH2CH2CH2OH など多数のNH2化合物が見つかっている• ビニルアミンC2H3NH2とエチルアミンC2H5NH2はこれまでISMで未検出だが、太陽系の隕石中で見つかっている（エチルアミンはcomet 81P/Wild2のコマでも検出）やったこと：• IRAM, Yebes telescopesを用いてλ＝2,3,7mmでG+0.693-0.027を観測• MADCUBA packageのSpectral Line Identi cation and Modeling (SLIM) tool を使っfifiて、得られたスペクトルを ttingし、ビニルアミン・エチルアミンの存在量を推定

ビニルアミンC2H3NH2• 9つのlineをSN>5で検出• そのうち5つは他の分子輝線とblendしていない• ブレンドしていない輝線もSN>20で検出しているので有意に検出エチルアミンC2H5NH2• 7つのlineをSN>4で検出• そのうち4つは他の分子輝線とblendしていない• ブレンドしていない輝線のSNが最大でも6なのでtentative
detection

他の星形成領域との比較• Orion KL, IRAS1629302422BはR-NH2に欠乏• G+0.693は他と比べ低温なのにR-NH2リッチ->低速度衝撃波によるsputteringが効いていると思われる

考えられる生成経路• ビニルアミン(C2H3NH2)はCH3NH2やC2H5NH2からガス相で形成される• エチルアミン(C2H5NH2)はダスト表面反応でしか形成されない-> 衝撃波によるsputteringによって放出https://arxiv.org/abs/2106.04593

25. A Revised Description of the Cosmic Ray-Induced Desorption of Interstellar Ices
O. Sipilä, K. Silsbee, P. Casellifi fi

fifi

Non-thermal desorption of ices on interstellar grains is required to explain observations of moleculesthat are not synthesized ef ciently in the gas phase in cold dense clouds. Perhaps the most important
non-thermal desorption mechanism is one induced by cosmic rays (CRs), which, when passing througha grain, heat it transiently to a high temperature - the grain cools back to its original equilibriumtemperature via the (partial) sublimation of the ice. Current cosmic-ray-induced desorption (CRD)
models assume a xed grain cooling time. In this work we present a revised description of CRD in
which the desorption ef ciency depends dynamically on the ice content. We apply the revised
desorption scheme to two-phase and three-phase chemical models in physical conditions
corresponding to starless and prestellar cores, and to molecular cloud envelopes. We nd that insidestarless and prestellar cores, introducing dynamic CRD can decrease gas-phase abundances by up to anorder of magnitude in two-phase chemical models. In three-phase chemical models our model
produces very similar results to the static cooling scheme - when only one monolayer of ice isconsidered active. Ice abundances are generally insensitive to variations in the grain cooling time.
Further improved CRD models need to take into account additional effects in the transient heating of
the grains, introduced for example by the adoption of a spectrum of CR energies.

https://arxiv.org/abs/2110.04270

26. VLA Observations of 9 Extended Green Objects in the Milky Way: UbiquitousWeak, Compact Continuum Emission, and Multi-Epoch Emission from CH3OH,H2O, and NH3 Masers
A. P. M. Towner, C. L. Brogan, T. R. Hunter, C. J. Cyganowski

fififi fi

fi

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We have observed a sample of 9 Extended Green Objects (EGOs) at 1.3 and 5 cm with the VLA with
sub-arcsecond resolution and 7-14 uJy/beam sensitivities in order to characterize centimeter continuum
emission as it rst appears in these massive protoclusters. We nd EGO-associated continuum
emission - within 1 arcsec of the extended 4.5 um emission - in every eld, which is typically faint(order 101-102 uJy) and compact (unresolved at 0.3-0.5 arcsec). The derived spectral indices of our 36
total detections are consistent with a wide array of physical processes, including both non-thermal(19% of detections) and thermal free-free processes (e.g. ionized jets and compact HII regions, 78% ofsample), and warm dust (1 source). We also nd EGO-associated 6.7 GHz CH3OH and 22 GHz H2O
maser emission in 100% of the sample, and NH3 (3,3) masers in 45%; we do not detect any NH3 (6,6)
masers at 5.6 mJy/beam sensitivity. We nd statistically-signi cant correlations between radio-distanceand bolometric luminosities at two physical scales and three frequencies, consistent with thermal
emission from ionized jets, but no correlation between water-maser and radio-distance luminosities forour sample. From these data, we conclude that EGOs likely host multiple different centimeter
continuum-producing processes simultaneously. Additionally, at our 1000 au resolution, we nd that
all EGOs except G18.89−0.47 contain 1 to 2 massive sources based on the presence of methanol masergroups, which is consistent with our previous work suggesting that these are typical massive
protoclusters in which only one to a few of the YSOs are massive.

https://arxiv.org/abs/2109.09765

28. On the Three-Dimensional Structure of Local Molecular Clouds
Catherine Zucker, Alyssa Goodman, João Alves, Shmuel Bialy, Eric W. Koch, Joshua S. Speagle,
Michael M. Foley, Douglas Finkbeiner, Reimar Leike, Torsten Enßlin, Joshua E. G. Peek, Gordian
Edenhofer

fififififififi fifi

We leverage the 1 pc spatial resolution of the Leike et al. 2020 3D dust map to characterize the threedimensional structure of nearby molecular clouds (d <~ 400 pc). We start by "skeletonizing" the clouds
in 3D volume density space to determine their "spines," which we project on the sky to constrain cloud
distances with ≈ 1% uncertainty. For each cloud, we determine an average radial volume density
pro le around its 3D spine and t the pro les using Gaussian and Plummer functions. The radial
volume density pro les are well-described by a two-component Gaussian function, consistent withclouds having broad, lower-density outer envelopes and narrow, higher-density inner layers. The ratioof the outer to inner envelope widths is ≈ 3 : 1. We hypothesize that these two components may be
tracing a transition between atomic and diffuse molecular gas or between the unstable and cold neutral
medium. Plummer-like models can also provide a good t, with molecular clouds exhibiting shallow
power-law wings with density, n, falling off like n−2 at large radii. Using Bayesian model selection,
we nd that parameterizing the clouds’ pro les using a single Gaussian is disfavored. We compare ourresults with 2D dust extinction maps, nding that the 3D dust recovers the total cloud mass fromintegrated approaches with delity, deviating only at higher levels of extinction (AV <~ 2−3 mag). The
3D cloud structure described here will enable comparisons with synthetic clouds generated insimulations, offering unprecedented insight into the origins and fates of molecular clouds in theinterstellar medium.