The Star Formation Newsletter #321 (60-68)
森 昇志 (東大)11/01

60. Magnetic fields in the infrared dark cloud G34.43+0.24
61. A study of accretion and disk diagnostics in the NGC 2264 cluster
62. Near-Infrared Imaging Polarimetry toward M17 SWex
63. S and VV Corona Australis: Spectroscopic Variability in Two Young Binary Star Systems
64. ALMA observations of fragmentation, sub-structure, and protostars in high-mass starlessclump candidates
65. Investigation of 13C Isotopic Fractionation of CCH in Two Starless Cores: L1521B and L134N
66. Multi-wavelength observations of protoplanetary discs as a proxy for the gas disc mass
67. Gravitoviscous protoplanetary disks with a dust component. II. Spatial distribution andgrowth of dust in a clumpy disk
68. Modeling Time Dependent Water Chemistry Due to Powerful X-ray Flares from T-Tauri Stars
69. Planetesimals to Terrestrial Planets: collisional evolution amidst a dissipating gas disk

66

Multi-wavelength observations of protoplanetary discs
as a proxy for the gas disc mass
B. Veronesi, G. Lodato, G. Dipierro, E. Ragusa, C. Hall, and D. J. Price流体シミュレーション• St が大きくなるにつれて、ダストはスパイラル構造から分離• H/R大きい方が円盤との相互作用小さくなり、スパイラルの振幅が小さい

模擬観測• St > 0.4 の時に、SPHERE模擬観測でスパイラル、ALMA模擬観測でリングを形成• St > 0.4 はΣgas < 0.4 g/cm2 に対応 à 円盤質量 = 1.4 x10-3 Msun
ALMA模擬観測

http://arxiv.org/abs/1908.08865

SPHERE模擬観測

69

Planetesimals to terrestrial planets:
Collisional evolution amidst a dissipating gas disk
Kevin J. Walsh, Harold F. Levison

背景手法• 惑星形成の描像：
暴走成長 (重力フォーカシング)
à 寡占成長 (stirring)à 巨大衝突• LIPAD(Levison+12):

粒子を集団として扱い、集団間の重力相互作用、集団内の粒子のサイズ変化を解く
月サイズ以上になったら１粒子として扱う• 従来研究は寡占成長段階(大量の微惑星+原始 • 衝突で生じた小さな破片は取り除く星)から始めた計算で最終惑星分布を議論• 標準モデル：
MMSN, 2Myr円盤散逸, 30km微惑星• いつ・どこで寡占成長段階が達成されるか？

http://arxiv.org/abs/1908.00897• 円盤散逸を考慮した微惑星から惑星までの一貫した衝突成長計算• 様々な条件で計算しても、従来計算の初期条件のような、シンプルな微惑星と原始惑星の２極分布は達成しない

• Inside-out成長は 衝突成長 + 円盤散逸 によって増幅• 極端なInside-out成長のために、異なる場所で同時に寡占成長段階にならない• < 1 au : 巨大衝突段階 ; > 2 au : 暴走成長段階• 成長時間が早いケース(2MMSN, 5km微惑星)では２極分布になるが(右図; ~5Myr)、質量分布はシンプルではない(0.7-1auに全質量の94%) ＋ 火星が重すぎる
暴走成長

http://arxiv.org/abs/1908.00897

巨大衝突We present the B-fields mapped in IRDC G34.43+0.24 using 850 μm polarized dust emission observed with the POL-2
instrument at JCMT. We examine the magnetic field geometries and strengths in the northern, central, and southern
regions of the filament. The overall field geometry is ordered and aligned closely perpendicular to the filament’s main axis,
particularly in regions containing the central clumps MM1 and MM2, whereas MM3 in the north has field orientationsaligned with its major axis. The overall field orientations are uniform at large (POL-2 at 14′′ and SHARP at 10′′) to smallscales (TADPOL at 2.5′ and SMA at 1.5′′) in the MM1 and MM2 regions. SHARP/CSO observations in MM3 at 350 μm
from Tang et al. show a similar trend as seen in our POL-2 observations. TADPOL observations demonstrate a welldefined field geometry in MM1/MM2 consistent with MHD simulations of accreting filaments. We obtained a plane-ofsky magnetic field strength of 470±190 μG, 100±40 μG, and 60±34 μG in the central, northern and southern regions ofG34, respectively, using

http://arxiv.org/abs/1908.03624

60

61

A study of accretion and disk diagnostics in the NGC 2264 cluster

Understanding disk dissipation is essential for studying how planets form. Disk gaps and holes, which almost
correspond to dust-free regions, are inferred from infrared observations of T Tauri stars (TTS), indicating theexistence of a transitional phase between thick accreting disks and debris disks. Transition disks are usually referred
to as candidates for newly formed planets. We searched for transition disk candidates belonging to NGC 2264. We
characterized accretion, disk, and stellar properties of transition disk candidates and compared them to systems with afull disk and diskless stars. We modeled the spectral energy distribution (SED) of a sample of 401 TTS, withHyperion SED fitting code using photometric data from the U band to the MIPS band. We used the SED modeling todistinguish transition disk candidates, full disk systems, and diskless stars. We classified 52% of the sample as fulldisk systems, 41% as diskless stars, and 7% of the systems as transition disk candidates, among which seven systems
are new transition disk candidates belonging to the NGC 2264 cluster. The sample of transition disk candidates
present dust in the inner disk similar to anemic disks, according to the αIRAC classification, which shows that anemic
disk systems can be candidate transition disks. We show that the presence of a dust hole in the inner disk does notstop the accretion process since 82% of transition disk candidates accrete and show Hα, UV excess, and massaccretion rates at the same level as full disk systems. We estimate the inner hole sizes, ranging from 0.1 to 78AU, forthe sample of transition disk candidates. In only 18% of the transition disk candidates, the hole size could be
explained by X-ray photoevaporation from stellar radiation.

• 若い星団NGC2644の遷移円盤の観測データを解析し特徴付けを行った• 52%がfull disks, 41%がdiskless stars, 7%が遷移円盤candidate• 遷移円盤のうち18%のみ、inner holeの大きさがX線光蒸発で説明できうる

http://arxiv.org/abs/1908.03487

Alana P. Sousa, Silvia H. P. Alencar, Luisa M. Rebull, Catherine C. Espaillat, Nuria Calvet and Paula S. Teixeira62

Near-Infrared Imaging Polarimetry toward M17 SWex

We conducted near-infrared (JHKs) imaging polarimetry toward the infrared dark cloud (IRDC) M17 SWex,including almost all of the IRDC filaments as well as its outskirts, with the polarimeter SIRPOL on the IRSF 1.4 mtelescope. We revealed the magnetic fields of M17 SWex with our polarization-detected sources that were selected bysome criteria based on their near-IR colors and the column densities toward them, which were derived from theHerschel data. The selected sources indicate not only that the ordered magnetic field is perpendicular to the cloudelongation as a whole, but also that at both ends of the elongated cloud the magnetic field appears to bent toward its
central part, i.e., large-scale hourglass-shaped magnetic field perpendicular to the cloud elongation. In addition to thisgeneral trend, the elongations of the filamentary subregions within the dense parts of the cloud appear to be mostlyperpendicular to their local magnetic fields, while the magnetic fields of the outskirts appear to follow the thinfilaments that protrude from the dense parts. The magnetic strengths were estimated to be ∼ 70−300 μG in thesubregions, of which lengths and average number densities are ∼3–9 pc and ∼2–7×103 cm−3, respectively, by theDavis-Chandrasekhar-Fermi method with the angular dispersion of our polarization data and the velocity dispersion
derived from the C18O (J = 1–0) data obtained by the Nobeyama 45 m telescope. These field configurations and ourmagnetic stability analysis of the subregions imply that the magnetic field have controlled the formation/evolution of
the M17 SWex cloud.

• 偏光観測によるIRDC M17 SWexの磁場強度・磁場構造の測定• 全体的にフィラメントの軸に対して垂直な整列磁場,磁場強度は70 -- 300 uG• フィラメントの端ではやや中心方向：large scaleなhourglass shape

http://arxiv.org/abs/1906.12138

Koji Sugitani, Fumitaka Nakamura, Tomomi Shimoikura, Kazuhito Dobashi, Quang Nguyen-Luong,
Takayoshi Kusune, Takahiro Nagayama, Makoto Watanabe, Shogo Nishiyama and Motohide Tamura

63

S and VV Corona Australis: Spectroscopic Variability
in Two Young Binary Star Systems

We used high-resolution near-infrared spectroscopy from the NIRSPEC instrument on the Keck II telescope, takenover multiple epochs spanning five years, to examine two young binary T Tauri star systems, S Corona Australis andVV Corona Australis. The stars in these 1′′–2′′ separation systems have optically thick circumstellar disks and highextinctions at optical and near-infrared wavelengths. Using a combination of new and archival data, we havedetermined the spectral types of all the stars in these two systems for the first time, examined the variable NIR veiling,measured the emission line equivalent widths, and created spectral energy distributions. They have similar spectral
types (K7–M1) and are at approximately the same evolutionary stage, allowing comparison of the four stars in thetwo systems. We conclude that S CrA and VV CrA are young binary systems of stars bridging the Class I and Class II
evolutionary stages, characterized by high accretion luminosities and variable emission lines.

• 高分解な近赤外観測によって、２つの若い連星(S CrA & VV CrA)のそれぞれのスペクトルタイプ

http://arxiv.org/abs/1908.06135

Kendall Sullivan, L. Prato, Suzan Edwards, Ian Avilez, and Gail H. Schaefer

64

ALMA observations of fragmentation, sub-structure,and protostars in high-mass star- less clump candidates

The initial physical conditions of high-mass stars and protoclusters remain poorly characterized. To this end we present thefirst targeted ALMA 1.3 mm continuum and spectral line survey towards high-mass starless clump candidates, selecting asample of 12 of the most massive candidates (400– 4000 M⊙) within 5 kpc. The joint 12+7 m array maps have a highspatial resolution of ∼3000 au (∼0.8′′) and have point source mass-completeness down to ∼0.3 M⊙ at 6σ (or 1σ column
density sensitivity of 1.1 × 1022 cm−2). We discover previously undetected signposts of low-luminosity star formationfrom CO (2–1) and SiO (5–4) bipolar outflows and other signatures towards 11 out of 12 clumps, showing that current
MIR/FIR Galactic Plane surveys are incomplete to low- and intermediate-mass protostars (<∼50 L⊙). We compare asubset of the observed cores with a suite of radiative transfer models of starless cores. We find a high-mass starless core
candidate with a model-derived mass consistent with 29+52 M⊙ when integrated over size scales −15 of 2 × 104 au.
Unresolved cores are poorly fit by starless core models, supporting the interpretation that they are protostellar even without
detection of outflows. Substantial fragmentation is observed towards 10 out of 12 clumps. We extract sources from themaps using a dendrogram to study the characteristic fragmentation length scale. Nearest neighbor separations whencorrected for projection are consistent with being equal to the clump average thermal Jeans length. Our findings support ahierarchical fragmentation process, where the highest density regions are not strongly supported against thermal
gravitational fragmentation by turbulence or magnetic fields• ALMA(1.3mm連続波+line)による大質量星なしクランプのサーベイ観測• 新たに低--中光度星形成の兆候を検出• 観測の星なしコアと輻射輸送を用いたモデルを比較し質量を見積もった

http://arxiv.org/abs/1908.10374

Brian E. Svoboda, Yancy L. Shirley, Alessio Traficante, Cara Battersby, Gary A. Fuller,
Qizhou Zhang, Henrik Beuther, Nicolas Peretto, Crystal Brogan, Todd Hunter

65

Investigation of 13C Isotopic Fractionation of CCH
in Two Starless Cores: L1521B and L134N

We have carried out observations of CCH and its two 13C isotopologues, 13CCH and C13CH, in the 84 – 88 GHz band
toward two starless cores, L1521B and L134N (L183), using the Nobeyama 45 m radio telescope. We have detected
C13CH with a signal-to-noise (S/N) ratio of 4, whereas no line of 13CCH was detected in either the dark clouds. Thecolumn densities of the normal species were derived to be (1.66 ± 0.18)×1014 cm−2 and (7.3 ± 0.9)×1013 cm−2 (1σ) inL1521B and L134N, respectively. The column density ratios of N(C13CH)/N(13CCH) were calculated to be > 1.1 and >1.4 in L1521B and L134N, respectively. The characteristic that 13CCH is less abundant than C13CH is likely common fordark clouds. Moreover, we find that the 12C/13C ratios of CCH are much higher than those of HC3N in L1521B by morethan a factor of 2, as well as in Taurus Molecular Cloud-1 (TMC-1). In L134N, the differences in the 12C/13C ratios
between CCH and HC3N seem to be smaller than those in L1521B and TMC-1. We discuss the origins of the 13C isotopic
fractionation of CCH and investigate possible routes that cause the significantly high 12C/13C ratio of CCH especially inyoung dark clouds, with the help of chemical simulations. The high 12C/13C ratios of CCH seem to be caused byreactions between hydrocarbons (e.g., CCH, C2H2, l,c-C3H) and C+.

• 星なしコアL1521B, L134Nに対するCCH, 13CCH, C13CHの観測• 13CCHは検出したがC13CH は未検出
• L1521では13CCHの12C/13がHC3Nより２倍ほど高かった

https://arxiv.org/pdf/1908.09983

Kotomi Taniguchi, Eric Herbst, Hiroyuki Ozeki and Masao Saito

Eduard Vorobyov and Vardan Elbakyan
Spatial distribution and growth of dust in a clumpy protoplanetary disk subject to vigorous gravitational instability andfragmentation is studied numerically with sub-au resolution using the FEOSAD code. Hydrodynamics equations describing theevolution of self-gravitating and viscous protoplanetary disks in the thin-disk limit were modified to include a dust component
consisting of two parts: sub-micron-sized dust and grown dust with a variable maximum radius. The conversion of small togrown dust, dust growth, friction of dust with gas, and dust self-gravity were also considered. We found that the disk
appearance is notably time-variable with spiral arms, dusty rings, and clumps, constantly forming, evolving, and decaying. Asa consequence, the total dust-to-gas mass ratio is highly non-homogeneous throughout the disk extent, showing order-ofmagnitude local deviations from the canonical 1:100 value. Gravitationally bound clumps formed through gravitational
fragmentation have a velocity pattern that deviates notably from the Keplerian rotation. Small dust is efficiently converted intogrown dust in the clump interiors, reaching a maximum radius of several decimeters. Concurrently, grown dust drifts towards
the clump center forming a massive compact central condensation (70–100 M⊕). We argue that protoplanets may form in theinteriors of inward-migrating clumps before they disperse through the action of tidal torques. We foresee the formation ofprotoplanets at orbital distances of several tens of au with initial masses of gas and dust in the protoplanetary seed in the (0.25–1.6) MJup and (1.0–5.5) M⊕ limits, respectively. The final masses of gas and dust in the protoplanets may however be muchhigher due to accretion from surrounding massive metal-rich disks/envelopes. Dusty rings formed through tidal dispersal ofinward-migrating clumps may have a connection to ring-like structures found in youngest and massive protoplanetary disks.
Numerical disk models with a dust component that can follow the evolution of gravitationally bound clumps through theircollapse phase to the formation of protoplanets are needed to make firm conclusions on the characteristics of planets forming
through gravitational fragmentation.

• 流体シミュレーション：重力不安定円盤におけるダストの分布と成長• ダストガス比は大きく時間・空間変動• クランプの潮汐破壊によってできるダストリングは若くて重い円盤のリング構造の原因かも

http://arxiv.org/abs/1908.10589

67

Gravitoviscous protoplanetary disks with a dust component. II.
Spatial distribution and growth of dust in a clumpy disk

68Modeling Time Dependent Water Chemistry
Due to Powerful X-ray Flares from T-Tauri Stars

Young stars emit strong flares of X-ray radiation that penetrate the surface layers of their associated protoplanetary disks.
It is still an open question as to whether flares create significant changes in disk chemical composition. We present
models of the time-evolving chemistry of gas-phase water during X-ray flaring events. The chemistry is modeled at point
locations in the disk between 1 and 50 au at vertical heights ranging from the mid-plane to the surface. We find thatstrong, rare flares, i.e., those that increase the unattenuated X-ray ionization rate by a factor of 100 every few years, cantemporarily increase the gas-phase water abundance relative to H can by more than a factor of ∼3–5 along the disk
surface (Z/R ≥ 0.3). We report that a “typical” flare, i.e., those that increase the unattenuated X-ray ionization rate by afactor of a few every few weeks, will not lead to significant, observable changes. Dissociative recombination of H3O+,
water adsorption and desorption onto dust grains, and ultraviolet photolysis of water and related species are found to be
the three dominant processes regulating the gas-phase water abundance. While the changes are found to be significant, wefind that the effect on gas phase water abundances throughout the disk is short-lived (days). Even though we do not see asubstantial increase in long term water (gas and ice) production, the flares’ large effects may be detectable as time varying
inner disk water ‘bursts’ at radii between 5 and 30 au with future far infrared observations.

•••
•
•

時間発展する化学反応計算：X線フレアによって観測で分かるほど水の存在量が変わるか？
強いフレア(数百年に一回規模)なら一時的に水の存在量は3-5倍増大
普通のフレア(数週間に一回規模)では観測できる程変わらない
上昇した水存在量のは数日の時間スケールで減衰
水のバースト現象として将来の遠赤外観測で受かるかも

http://arxiv.org/abs/1908.08048

Abygail R. Waggoner and L. Ilsedore Cleeves