THE STAR FORMATION NEWSLETTER No. 357, 10-18 2022/12/16
泉奈都子（ASIAA）
10.Complex Organic Molecules Formation in Cold Cores on Stochastically Heated Grains 11.CHEMOUT: CHEMical complexity in star-forming regions of the OUTer Galaxy III. Nitrogen isotopic ratios in the outer Galaxy 12.The Great Planetary Heist: Theft and capture in star-forming regions 13.Thermophysical evolution of planetesimals in the Primordial Disk 14.The formation of clusters and OB associations in different density spiral arm environments 15.Accretion Burst Echos as Probes of Protostellar Environments and Episodic Mass Assembly 16.Accretion and extinction variations in the low-mass pre-main sequence binary system WX Cha 17. The relation between the Mass Accretion Rate and the Disk Mass in Class I Protostars 18.Different degrees of nitrogen and carbon depletion in the warm molecular layers of protoplanetary disk
•異なる環境を持つspiral armにおけるcluster形成と進化をシミュレーションで検証• Dobbs et al. 2022, MNRAS 509, 954-973の続きの論文(詳細はこちらに書かれている) ▸本論文では初期のガス質量を小さくし、かつsupernovaを含めた再検証を行った-シミュレーションコード: Smoothed Particle Hydrodynamics (SPH) code sphNG (sink particle, cooling, heating, stellar feed backを含む) - stellar disk全体はstar particleでモデル化、選択した領域のみgas particleも含む- ハロー：NFW potential - Gas : self gravity, heating, cooling, H2, CO chemistry - Sink particleはgas densities > 1000 cm 3でかつgasが収束、結合されたら（Bate et al. 1995）生成される(gas densities ~ 105cm 3で強制的に生成) - Sink radius: 0.1 pc, merger radius: 0.001 pc, Sinc mass: ~ 10 Msun order - Stellar feed back
Dobbs et al. (2022)で実行済み● Results
▸ Feed backがある方がclusterの半径を増加させ（gasを飛ばすことによりgravitational potentialが減少し、 cluster半径が大きくなる）、かつmass-radius relationをよく再現する• Results ▸ Supernovaの影響は小さい(ionizationによってできた低ガス密度領域をより低密度で熱いガスで満たすだけ▸どのようなモデルでもclusterのmerge, splitは起こるHot gas 14 Myr
● Protostarの時間変動をsub-mm/mm light curveを用いて検証▸ far-IRはaccretion luminosityの変動、sub-mm/mmはenvelopeの温度の変動を示す● Target: Serpens Main star-forming region (d = 436 pc) • Telescope: ALMA ACA (Band 7 cont, res~4"), SMA (230/240 GHz, cont, res~3"), JCMT (850μm, res. ~15.6") EC 53: Main target, Class I protostar, periodic outburst検出Table 1. Science Targets and YSO Calibrators
calibration用天体(SMM9は変動が検出、SMM2は暗すぎるため除外) Logan Francis et al.
● Calibration
▸通常のquasars等を用いたcalibrationの精度は10-20 ％ ▸本研究では、より精度の高いRelative flux calibrationを使用-明るくかつ変動のないYSOを用いたcalibration方法(Francis et al. 2020) - UV平面上で点源モデルを用いたχ²フィットを各calibrator, epochで行う● Light curve ▶ ACA vs. JCMT
- ACAではEC53, SMM10において変動を検出(ACAで見られるflux変動の幅の方が大きい) - EC53において、SMAの方がより高いピークflux値を示し、かつより早く減少に転じている● Light curve model (EC53) ▸ 2 Dモデルを使用して、SMA（ACA）とJCMTの観測結果の違いを検証- ACA, SMAはinner envelope (~1500 au)におけるaccretionの変動を検出していると考えられる- JCMTはよりcoldかつless denseなenvelope material (~ 3000au)を含み、ゆえに外部からの星間放射の影響を受け、かつ中心星からの放射にも時間がかかると考えられるEnvelope profile ρ(r) = ρο(r/ro)α, Dust temperature (T iloor <= heating from external interstellar radiation field, t i ь: lookback time ) T(t,r) = Luminosity
ne) ● Light curve model (EC53) ▸ model vs. observation - modelは観測結果をよく再現している- JCMTはTfloor (external interstellar radiation field)に大きく左右される(ピーク値) - Shallower profile (α = -0.5)だとピーク値が減少(colder dustの量の増加によるもの) - routを小さくすると、cold materialが減るため, JCMTのピーク値が増加
● Light curve model
▸ Different outerburst behavior I vs. beam size -周期の早い変動はlarge beamでは不明瞭になる(case: SMM 10)
Elenora Fiorellino et al. • Class I YSOにおけるMass accretion rateとDisk massの関係を始めて観測的に検証• Target: d = 500pc以内に位置し、NIR spectroscopic data (for accretion analysis)とmillimeter data (for disk dust mass)の両方が得られた26天体を過去の研究から選出した(Class I天体の中でも明るくかつ進化が進んでいるもの)
NOTE—°Parallax distance with Gaia EDR3 direct match (Gaia Collaboration et al. 2021), Distance to the region (error is set to 10% if not stated in literature): b Ortiz-León et al. (2018), c Krolikowski et al. (2021), d assumed to be the same as FS TauA where Gaia EDR3 is available, cTobin et al. (2020). References:  1 - Nisini et al. (2005b), 2 - Antoniucci et al. (2008), 3 - Fiorellino et al. (2021), 4 - ALMA#2019.1.01792.S, 5 - Tobin et al. (2020), Zhang et al. (2016), 6 - Tychoniec et al. (2020), 7-Tobin et al. (2018), 8-Yang et al. (2021), 9-Akeson & Jensen (2014), 10-Sheehan & Eisner (2017), 11 - Akeson et al. (2019), 12 - Villenave et al. (2020), 13 - van 't Hoff et al. (2020), 14 - ALMA#2019.1.01813.S, 15 - Tobin et al. (2020). Mass accretion rates correspond to the range of values inferred assuming the age varying from the birthline to 1 Myr. (1) Age = Birthline - 1Myrで計算
d² F v (2) Kv(β)Bv(Tdust) ▸ Class IのMaccはClass IIよりも大きい▶ Fitted slope - Class I all: log(Macc) = (0.3±0.2)log(Mdisk)+(-6.3±0.3) Standard deviation: 0.4±0.1 - Class II all, Slope: 0.7±0.2 - Class I (remove two small Mdisk source), Slope: 1.1±0.2 Class Iの傾きの方が平らな傾向にあるが、Mdiskの小さい天体のサンプルを増やした検証が必須である● Macc VS. Mdisk ▸ Class Iの方がdisk depletion time (Macc/Mdisk)が早い→ Class Iの段階でdepletion timeが一定であればdiskは105-106 yrで無くなるはずだが、実際には106-107 yrまで残っているMaccは一定でなく、進化が進むにつれて急激に減少するii. Maccは一定であるが、envelopeからextra massを得る▸ Disk evolution modelの検証- Viscous model  (Lodato et al. 2017) _ Mo  / Mdisk Macc = 2(2 - γ) t ν  \ ¯ Mo - Hybrid model (Viscous + MHD wind, Tabone et al. 2021) / Mdisk Macc = Macc,0 (4) - MHD wind model (Tabone et al. 2021) Macc = Macc,0
(5)
Long-Fei Chen et al.
ABSTRACT
We investigate the roles of stochastic grain heating in the formation of complex organic molecules (COMs) in cold cores, where COMs have been detected. Two different types of grain-size distributions are used in the chemical models. The first one is the MRN distribution, and the second one considers grain coagulation to study its effects on the chemical evolution in these environments. The macroscopic Monte Carlo method is used to perform the two-phase chemical model simulations. We find that (1) grain coagulation can affect certain gas-phase species, such as CO₂ and N₂H+, in the cold core environments, which can be attributed to the volatile precursors originating from the small grains with temperature fluctuations; (2) grains with radii around 4.6 × 10-3 μm contribute most to the production of COMs on dust grains under cold core conditions, while few species can be formed on even smaller grains with radii less than 2 × 10−3 μm; (3) COMs formed on stochastically heated grains could help explain the observed abundances of gas-phase COMs in cold cores. Key words:  astrochemistry – ISM: abundances – ISM: molecules
L. Colzi et al.
ABSTRACT
Context. Nitrogen isotopic ratios are a key tool for tracing Galactic stellar nucleosynthesis. Aims. We present the first study of the 14N/15N abundance ratio in the outer regions of the Milky Way (namely, for galactocentric distances, R GC , from 12 kpc up to 19 kpc), with the aim to study the stellar nucleosynthesis effects in the global Galactic trend. Methods. We analysed IRAM 30m observations towards a sample of 35 sources in the context of the CHEMical complexity in star- forming regions of the OUTer Galaxy (CHEMOUT) project. We derived the 14 N/15N ratios from HCN and HNC for 14 and 3 sources, respectively, using the J = 1–0 rotational transition of HN13C, H15NC, H13CN, and HC15N. Results. The results found in the outer Galaxy have been combined with previous measurements obtained in the inner Galaxy. We find an overall linear decreasing H 13 CN/HC 15 N ratio with increasing RGC. This translates to a parabolic 14 N/15 N ratio with a peak at 11 kpc. Updated Galactic chemical evolution models have been taken into account and compared with the observations. The parabolic trend of the ¹⁴N/¹³N ratio with RGc can be naturally explained (i) by a model that assumes novae as the main ¹³N producers on long timescales (≥1 Gyr) and (ii) by updated stellar yields for low- and intermediate-mass stars. Key words.  Galaxy: abundances – Galaxy: evolution – (Galaxy:) local interstellar matter – ISM: abundances –ISM: molecules – radio lines: ISM

Emma C. Daffern-Powell et al.
ABSTRACT
Gravitational interactions in star-forming regions are capable of disrupting and destroying planetary systems, as well as creating new ones. In particular, a planet can be stolen, where it is directly exchanged between passing stars during an interaction; or captured, where a planet is first ejected from its birth system and is free-floating for a period of time, before being captured by a passing star. We perform sets of direct N -body simulations of young, substructured star- forming regions, and follow their evolution for 10 Myr in order to determine how many planets are stolen and captured, and their respective orbital properties. We show that in high density star-forming regions, stolen and captured planets have distinct properties. The semimajor axis distribution of captured planets is significantly skewed to wider orbits compared to the semimajor axis distribution of stolen planets and planets that are still orbiting their parent star (preserved planets). However, the eccentricity and inclination distributions of captured and stolen planets are similar, but in turn very different to the inclination and eccentricity distributions of preserved planets. In low-density star-forming regions these differences are not as distinct but could still, in principle, be used to determine whether observed exoplanets have likely formed in situ or have been stolen or captured. We find that the initial degree of spatial and kinematic substructure in a star-forming region is as important a factor as the stellar density in determining whether a planetary system will be altered, disrupted, captured or stolen. Key words:  methods: numerical – planets and satellites: dynamical evolution and stability – stars: kinematics and dynamics
Bjorn J. R. Davidsson
ABSTRACT
The Primordial Disk of small icy planetesimals, once located at 15–30 AU from the Sun, was disrupted by giant planet migration in the early Solar System. The Primordial Disk thereby became the source region of objects in the current–day Kuiper Belt, Scattered Disk, and Oort Cloud. I present the thermophysics code "Numerical Icy Minor Body evolUtion Simulator", or NIMBUS, and use it to study the thermophysical evolution of planetesimals in the Primordial Disk prior to its disruption. Such modelling is mandatory in order to understand the behaviour of dynamically new comets from the Oort Cloud, as well as the activity of Centaurs and short–period comets from the Scattered Disk, that return pre–processed to the vicinity of the Sun. I find that bodies in the midst of the Primordial Disk with diameters ranging 4–200 km lost all their CO ice on time-scales of order 0.1–10 Myr depending on size, through a combination of protosolar and long–lived radionuclide heating. CO and other hypervolatiles therefore require a less volatile host for their storage. I consider two possible hosts: amorphous water ice and CO 2 ice. Because of the high luminosity of the protosun, some Primordial Disk bodies may have sustained significant crystallisation, CO : CO 2 segregation, and CO 2 sublimation in the uppermost few tens of meters. I discuss how this may affect coma abundance ratios and distant activity in dynamically new comets. Key words:  methods: numerical – comets: general – Kuiper belt: general – Oort Cloud – protoplanetary discs

Elenora Fiorellino et al.
ABSTRACT
Light curves of young star systems show photometric variability due to different kinematic, and physical processes.  One of the main contributors to the photometric variability is the changing mass accretion rate, which regulates the interplay between the forming young star and the protoplanetary disk.  We collected high-resolution spectroscopy in eight different epochs, as well as ground-based and space-borne multi-epoch optical and infrared photometry of WX Cha, an M0 binary system, with an almost edge-on disk ( i = 87°) in the ChamaeleonI star-forming region.  Spectroscopic ob- servations cover 72 days, the ground-based optical monitoring covers 42 days while space-borne TESS photometry extends for 56 days.  The multi-wavelength light curves exhibit quasi-periodic variabil- ity of 0.35 — 0.53mag in the near-infrared, and of 1.3mag in g band.  We studied the variability of selected emission lines that trace the accretion, computed the accretion luminosity and the mass accretion rate using empirical relations and obtained values between Lacc ～ 1.6 L ⊙ − 3.2 L ⊙ and Macc ～ 3.31 × 10-7 Mo/yr — 7.76 × 10-7 Mo/yr.  Our results show that WX Cha is accreting at a rate larger than what is typical for T Tauri stars in the same star-forming region with the same stellar parameters. We theorize that this is due to the higher disk mass of WX Cha than what is usual for stars with similar stellar mass, and to the binary nature of the system. Daily changes in the accretion luminosity and in the extinction can explain the photometric variability. Keywords: T Tauri stars, Accretion, Binary stars, Star formation, Spectroscopy, Light curves, Pho- tometry

ABSTRACT
Kenji Furuya et al.
Observations have revealed that the elemental abundances of carbon and oxygen in the warm molec- ular layers of some protoplanetary disks are depleted compared to those is the interstellar medium by a factor of ～10-100. Meanwhile, little is known about nitrogen. To investigate the time evolution of nitrogen, carbon, and oxygen elemental abundances in disks, we develop a one-dimensional model that incorporates dust settling, turbulent diffusion of dust and ices, as well as gas-ice chemistry including the chemistry driven by stellar UV/X-rays and the galactic cosmic rays. We find that gaseous CO in the warm molecular layer is converted to CO2 ice and locked up near the midplane via the combina- tion of turbulent mixing (i.e., the vertical cold finger effect) and ice chemistry driven by stellar UV photons. On the other hand, gaseous N 2 , the main nitrogen reservoir in the warm molecular layer, is less processed by ice chemistry, and exists as it is. Then the nitrogen depletion occurs solely by the vertical cold finger effect of N 2 . As the binding energy of N 2 is lower than that of CO and CO 2 , the degree of nitrogen depletion is smaller than that of carbon and oxygen depletion, leading to higher elemental abundance of nitrogen than that of carbon and oxygen. This evolution occurs within 1 Myr and proceeds further, when the α parameter for the diffusion coefficient is ～10−³. Consequently, the N2H†/CO column density ratio increases with time. How the vertical transport affects the midplane ice composition is briefly discussed. Keywords: astrochemistry — protoplanetary disks — ISM: molecules