記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/mnras/sty3524

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/mnras/stz1079

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/aae4dc

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/aacf9b

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/aac898

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/mnras/stx3070

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/mnras/stx2589

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We report ALMA observations in 0.87 mm continuum and ¹²CO (J = 3-2) toward a very low-luminosity (<0.1 L _o) protostar, which is deeply embedded in one of the densest cores, MC27/L1521F, in Taurus with an indication of multiple star formation in a highly dynamical environment. The beam size corresponds to ∼20 au, and we have clearly detected blueshifted/redshifted gas in ¹²CO associated with the protostar. The spatial/velocity distributions of the gas show there is a rotating disk with a size scale of ∼10 au, a disk mass of ∼10^-4 M _o, and a central stellar mass of ∼0.2 M _o. The observed disk seems to be detached from the surrounding dense gas, although it is still embedded at the center of the core whose density is ∼10⁶ cm^-3. The current low-outflow activity and the very low luminosity indicate that the mass accretion rate onto the protostar is extremely low in spite of a very early stage of star formation. We may be witnessing the final stage of the formation of ∼0.2 M _o protostar. However, we cannot explain the observed low luminosity with the standard pre-main-sequence evolutionary track unless we assume cold accretion with an extremely small initial radius of the protostar (∼0.65 ). These facts may challenge our current understanding of the low mass star formation, in particular the mass accretion process onto the protostar and the circumstellar disk.

DOI： 10.3847/1538-4357/aa8e9e

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/aa8264

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/2041-8213/aa9701

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/mnras/stx893

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/aa6a1c

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1038/s41550-017-0146

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/2041-8213/835/1/L11

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/pasj/psx113

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/833/2/238

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/MNRAS/STW1994

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/0004-637X/826/1/26

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/mnras/stw2256

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0004-637X/812/1/27

記述言語：英語  

DOI： 10.1088/2041-8205/810/2/L26

記述言語：英語  

DOI： 10.1093/mnras/stv1290

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/mnras/stu2633

その他リンク： http://ads.nao.ac.jp/abs/2015MNRAS.448.1405M

記述言語：英語  

DOI： 10.1088/0004-637X/801/2/117

記述言語：英語  

DOI： 10.1093/mnras/stu2160

記述言語：英語  

DOI： 10.1088/0004-637X/796/2/131

記述言語：英語  

DOI： 10.1088/2041-8205/796/1/L17

記述言語：英語  

DOI： 10.1088/0004-637X/793/1/1

記述言語：英語  

DOI： 10.1088/2041-8205/789/1/L4

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0004-637X/784/2/109

その他リンク： http://ads.nao.ac.jp/abs/2014ApJ...784..109T

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/mnras/stt2343

その他リンク： http://ads.nao.ac.jp/abs/2014MNRAS.438.2278M

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/mnras/stt1684

その他リンク： http://ads.nao.ac.jp/abs/2013MNRAS.436.1667T

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/mnras/stt1524

その他リンク： http://ads.nao.ac.jp/abs/2013MNRAS.435.3283M

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0004-637X/770/1/71

その他リンク： http://ads.nao.ac.jp/abs/2013ApJ...770...71T

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/2041-8205/750/2/L29

その他リンク： http://ads.nao.ac.jp/abs/2012ApJ...750L..29S

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1111/j.1365-2966.2011.20336.x

その他リンク： http://ads.nao.ac.jp/abs/2012MNRAS.421..588M

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0004-637X/747/1/47

その他リンク： http://ads.nao.ac.jp/abs/2012ApJ...747...47T

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1111/j.1365-2966.2011.19081.x

その他リンク： http://ads.nao.ac.jp/abs/2011MNRAS.416..591T

記述言語：英語   掲載種別：研究論文（学術雑誌）  

その他リンク： http://ads.nao.ac.jp/abs/2011PASJ...63..555M

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

出版者・発行元：Astrophysical Journal  

We perform a long-term simulation of star and disk formation using three-dimensional nonideal magnetohydrodynamics. The simulation starts from a prestellar cloud and proceeds through the long-term evolution of the circumstellar disk until ∼1.5 × 105 yr after protostar formation. The disk has size ≲50 au and little substructure in the main accretion phase because of the action of magnetic braking and the magnetically driven outflow to remove angular momentum. The main accretion phase ends when the outflow breaks out of the cloud, causing the envelope mass to decrease rapidly. The outflow subsequently weakens as the mass accretion rate also weakens. While the envelope-to-disk accretion continues, the disk grows gradually and develops transient spiral structures, due to gravitational instability. When the envelope-to-disk accretion ends, the disk becomes stable and reaches a size ≳300 au. In addition, about 30% of the initial cloud mass has been ejected by the outflow. A significant finding of this work is that after the envelope dissipates a revitalization of the wind occurs, and there is mass ejection from the disk surface that lasts until the end of the simulation. This mass ejection (or disk wind) is generated because the magnetic pressure significantly dominates both the ram pressure and thermal pressure above and below the disk at this stage. Using the angular momentum flux and mass-loss rate estimated from the disk wind, the disk dissipation timescale is estimated to be ∼106 yr.

DOI： 10.3847/1538-4357/ad4997

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出版者・発行元：Monthly Notices of the Royal Astronomical Society: Letters  

The detection of Keplerian rotation is rare among Class 0 protostellar systems. We have investigated the high-density tracer HCN as a probe of the inner disc in a Class 0 proto-brown dwarf candidate. Our ALMA high angular resolution observations show the peak in the HCN (3-2) line emission arises from a compact component near the proto-brown dwarf with a small bar-like structure and a deconvolved size of ∼50 au. Radiative transfer modelling indicates that this HCN feature is tracing the innermost, dense regions in the proto-brown dwarf where a small Keplerian disc is expected to be present. The limited velocity resolution of the observations, however, makes it difficult to confirm the rotational kinematics of this feature. A brightening in the HCN emission towards the core centre suggests that HCN can survive in the gas phase in the inner, dense regions of the proto-brown dwarf. In contrast, modelling of the HCO+ (3-2) line emission indicates that it originates from the outer pseudo-disc/envelope region and is centrally depleted. HCN line emission can reveal the small-scale structures and can be an efficient observational tool to study the inner disc properties in such faint compact objects where spatially resolving the disc is nearly impossible.

DOI： 10.1093/mnrasl/slae044

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記述言語：英語  

DOI： 10.1002/smtd.202301163

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PubMed

出版者・発行元：Astrophysical Journal  

We report Atacama Large Millimeter/submillimeter Array/Atacama Compact Array observations of a high-density region of the Corona Australis cloud forming a young star cluster, and the results of resolving internal structures. In addition to embedded Class 0/I protostars in the continuum, a number of complex dense filamentary structures are detected in the C18O and SO lines by the 7 m array. These are substructures of the molecular clump that are detected by the total power array as extended emission. We identify 101 and 37 filamentary structures with widths of a few thousand astronomical units in C18O and SO, respectively, which are called feathers. The typical column density of the feathers in C18O is about 1022 cm−2, and the volume density and line mass are ∼105 cm−3 and a few M ☉ pc−1, respectively. This line mass is significantly smaller than the critical line mass expected for cold and dense gas. These structures have complex velocity fields, indicating a turbulent interior. The number of feathers associated with Class 0/I protostars is only ∼10, indicating that most of them do not form stars but rather are transient structures. The formation of feathers can be interpreted as a result of colliding gas flow because the morphology is well reproduced by MHD simulations, and this is supported by the presence of H i shells in the vicinity. The colliding gas flows may accumulate gas and form filaments and feathers, and trigger the active star formation of the R CrA cluster.

DOI： 10.3847/1538-4357/ad40a6

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Astrophysical Journal  

The principal regular satellites of gas giants are thought to be formed by the accumulation of solid materials in circumplanetary disks (CPDs). While there has been significant progress in the study of satellite formation in CPDs, details of the supply of satellite building blocks to CPDs remain unclear. We perform the orbital integration of solid particles in the protoplanetary disk (PPD) approaching a planet, considering the gas drag force by using the results of three-dimensional hydrodynamical simulations of a local region around the planet. We investigate the planetary mass dependence of the capture positions and the capture rates of dust particles accreting onto the CPD. We also examine the degree of dust retention in the accreting gas onto the CPD, which is important for determining the ratio of the dust-to-gas inflow rates, a key parameter in satellite formation. We find that the degree of dust retention increases with increasing planetary mass for a given dust scale height in the PPD. In the case of a small planet (M p = 0.2M Jup), most particles with insufficient initial altitudes in the PPD are isolated from the gas in the accreting region. On the other hand, in the case of a massive planet (M p = 1M Jup), dust particles can be coupled to the vertically accreting gas, even when the dust scale height is about 10%-30% of the gas scale height. The results of this study can be used for models of dust delivery and satellite formation in the CPDs of gas giants of various masses, including exoplanets.

DOI： 10.3847/1538-4357/ad4035

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その他リンク： https://iopscience.iop.org/article/10.3847/1538-4357/ad4035/pdf

掲載種別：研究論文（学術雑誌）   出版者・発行元：Astrophysical Journal  

We present the results of our mosaic observations of a single Class 0 protostar IRAS 15398−3359 with the Atacama Compact Array in the CO J = 2-1 line. The new observations covering a ∼ 2 ′ square region reveal elongated redshifted and blueshifted components, which are located at distances of ∼30″-75″ on the northern and southern sides of the protostar, respectively, in addition to the previously observed primary and secondary outflows. These elongated components exhibit Hubble-law-like velocity structures, i.e., an increase of velocity with increasing distance from the protostar, suggesting that they comprise the third outflow associated with the protostar. Besides, a new redshifted component is detected at radii of ∼40″-75″ on the northwestern side of the protostar. This redshifted component also exhibits a Hubble-law-like velocity profile, which could be a counterpart of the secondary outflow mostly detected at blueshifted velocities in a previous study. The three outflows are all misaligned by ∼20°-90°, and the dynamical timescale of the primary outflow is shorter than those of the other outflows, approximately by an order of magnitude. These facts hint that the outflow launch direction has significantly changed with time. The outflow direction may change if the rotational axis and the magnetic field are misaligned or if the dense core is turbulent. We favor the second scenario as the origin of the multiple outflows in IRAS 15398−3359, based on a comparison between the observational results and numerical simulations.

DOI： 10.3847/1538-4357/ad34b7

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Astrophysical Journal  

Recent Atacama Large Millimeter/submillimeter Array (ALMA) observations have revealed an increasing number of compact protostellar disks with radii of less than a few tens of astronomical units and that young Class 0/I objects have an intrinsic size diversity. To deepen our understanding of the origin of such tiny disks, we have performed highest-resolution configuration observations with ALMA at a beam size of ∼0.″03 (4 au) on the very low-luminosity Class 0 protostar embedded in the Taurus dense core MC 27/L1521F. The 1.3 mm continuum measurement successfully resolved a tiny, faint (∼1 mJy) disk with a major axis length of ∼10 au, one of the smallest examples in the ALMA protostellar studies. In addition, we detected spike-like components in the northeastern direction at the disk edge. Gravitational instability or other fragmentation mechanisms cannot explain the structures, given the central stellar mass of ∼0.2 M ⊙ and the disk mass of ≳10−4 M ⊙. Instead, we propose that these small spike structures were formed by a recent dynamic magnetic flux transport event due to interchange instability that would be favorable to occur if the parental core has a strong magnetic field. The presence of complex arc-like structures on a larger (∼2000 au) scale in the same direction as the spike structures suggests that the event was not single. Such episodic, dynamical events may play an important role in maintaining the compact nature of the protostellar disk in the complex gas envelope during the main accretion phase.

DOI： 10.3847/1538-4357/ad2f9a

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Astrophysical Journal  

Outflows play a pivotal role in star formation as one of its most visible markers and a means of transporting mass, momentum, and angular momentum from the infalling gas into the surrounding molecular cloud. Their wide reach (at least thousands of astrnomical units) is a contrast to typical disk sizes (∼10–100 au). We employ high-resolution three-dimensional nested-grid nonideal magnetohydrodynamic (MHD) simulations to study outflow properties in the Class 0 phase. We find that no disk wind is driven from the extended centrifugal disk that has weak magnetic coupling. The low-velocity winds emerge instead from the infalling magnetic pseudodisk. Much of the disk actually experiences an infall of matter rather than outflowing gas. Some of the pseudodisk wind (PD-wind) moves inward to regions above the disk and either falls onto the disk or proceeds upward. The upward flow gives the impression of a disk wind above a certain height even if the gas is originally emerging from the pseudodisk. The PD-wind has the strongest flow coming from a disk interaction zone that lies just outside the disk and is an interface between the inwardly advected magnetic field of the pseudodisk and the outwardly diffusing magnetic field of the disk. The low-velocity wind exhibits the features of a flow driven by the magnetic pressure gradient force in some regions and those of a magnetocentrifugal wind in other regions. We interpret the structure and dynamics of the outflow zone in terms of the basic physics of gravity, angular momentum, magnetic fields, and nonideal MHD.

DOI： 10.3847/1538-4357/ad1bf3

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出版者・発行元：Monthly Notices of the Royal Astronomical Society  

Spirals and streamers are the hallmarks of mass accretion during the early stages of star formation. We present the first observations of a large-scale spiral and a streamer towards a very young brown dwarf candidate in its early formation stages. These observations show, for the first time, the influence of external environment that results in asymmetric mass accretion via feeding filaments on to a candidate proto-brown dwarf in the making. The impact of the streamer has produced emission in warm carbon-chain species close to the candidate proto-brown dwarf. Two contrasting scenarios, a pseudo-disc twisted by core rotation and the collision of dense cores, can both explain these structures. The former argues for the presence of a strong magnetic field in brown dwarf formation while the latter suggests that a minimal magnetic field allows large-scale spirals and clumps to form far from the candidate proto-brown dwarf.

DOI： 10.1093/mnras/stae724

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Astrophysical Journal  

We present molecular line observations of the protostellar outflow associated with HH270mms1 in the Orion B molecular cloud with ALMA. The 12CO (J = 3−2) emissions show that the outflow velocity structure consists of four distinct components of low (≲10 km s−1), intermediate (∼10-25 km s−1) and high (≳40 km s−1) velocities in addition to the entrained gas velocity (∼25-40 km s−1). The high- and intermediate-velocity flows have well-collimated structures surrounded by the low-velocity flow. The chain of knots is embedded in the high-velocity flow or jet, which is the evidence of episodic mass ejections induced by time-variable mass accretion. We could detect the velocity gradients perpendicular to the outflow axis in both the low- and intermediate-velocity flows. We confirmed the rotation of the envelope and disk in the 13CO and C17O emission and found that their velocity gradients are the same as those of the outflow. Thus, we concluded that the velocity gradients in the low- and intermediate-velocity flows are due to the outflow rotation. Using observational outflow properties, we estimated the outflow launching radii to be 67.1-77.1 au for the low-velocity flow and 13.3-20.8 au for the intermediate-velocity flow. Although we could not detect the rotation in the jets due to the limited spatial resolution, we estimated the jet launching radii to be (2.36-3.14) × 10−2 au using the observed velocity of each knot. Thus, the jet is driven from the inner disk region. We could identify the launching radii of distinct velocity components within a single outflow with all the prototypical characteristics expected from recent theoretical works.

DOI： 10.3847/1538-4357/ad19ce

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Astrophysical Journal  

We present ∼0.″2 (∼80 au) resolution observations of the CO(2-1) and SiO(5-4) lines made with the Atacama large millimeter/submillimeter array toward an extremely young intermediate-mass protostellar source (t dyn < 1000 yr), MMS 1 located in the Orion Molecular Cloud-3 region. We have successfully imaged a very compact CO molecular outflow associated with MMS 1, having deprojected lobe sizes of ∼1800 au (redshifted lobe) and ∼2800 au (blueshifted lobe). We have also detected an extremely compact (≲1000 au) and collimated SiO protostellar jet within the CO outflow. The maximum deprojected jet speed is measured to be as high as 93 km s−1. The SiO jet wiggles and displays a chain of knots. Our detection of the molecular outflow and jet is the first direct evidence that MMS 1 already hosts a protostar. The position-velocity diagram obtained from the SiO emission shows two distinct structures: (i) bow shocks associated with the tips of the outflow, and (ii) a collimated jet, showing the jet velocities linearly increasing with the distance from the driving source. Comparisons between the observations and numerical simulations quantitatively share similarities such as multiple-mass ejection events within the jet and Hubble-like flow associated with each mass ejection event. Finally, while there is a weak flux decline seen in the 850 μm light curve obtained with the James Clerk Maxwell Telescope/SCUBA 2 toward MMS 1, no dramatic flux change events are detected. This suggests that there has not been a clear burst event within the last 8 yr.

DOI： 10.3847/1538-4357/ad2268

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Astrophysical Journal  

We present the Atacama Large Millimeter/submillimeter Array observations of linearly polarized 1.1 mm continuum emission at ∼0.″14 (55 au) resolution and CO (J = 2−1) emission at ∼1.″5 (590 au) resolution toward one prestellar (MMS 4), four Class 0 (MMS 1, MMS 3, MMS 5, and MMS 6), one Class I (MMS 7), and one flat-spectrum (MMS 2) sources in the Orion Molecular Cloud 3 region. The dust disk-like structures and clear CO outflows are detected toward all sources except for MMS 4. The diameters of these disk-like structures, ranging from 16 to 97 au, are estimated based on the deconvolved full width half maximum (FWHM) values obtained from the multi-Gaussian fitting. Polarized emissions are detected toward MMS 2, MMS 5, MMS 6, and MMS 7, while no polarized emission is detected toward MMS 1, MMS 3, and MMS 4. MMS 2, MMS 5, and MMS 7 show organized polarization vectors aligned with the minor axes of the disk-like structures, with mean polarization fractions ranging from 0.6% to 1.2%. The strongest millimeter source, MMS 6, exhibits complex polarization orientations and a remarkably high polarization fraction of ∼10% around the Stokes I peak, and 15%-20% on the arm-like structure, as reported by Takahashi et al. (2019). The origins of the polarized emission, such as self-scattering and dust alignment due to the magnetic field or radiative torque, are discussed for individual sources. Some disk-like sources exhibit a polarized intensity peak shift toward the nearside of the disk, which supports that the polarized emission originates from self-scattering.

DOI： 10.3847/1538-4357/ad182d

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Astrophysical Journal  

WL 17 is a Class I object and was considered to have a ring–hole structure. We analyzed the structure around WL 17 to investigate the detailed properties of this object. We used Atacama Large Millimeter/submillimeter Array archival data, which have a higher angular resolution than previous observations. We investigated the WL 17 system with the 1.3 mm dust continuum and 12CO and C18O (J = 2–1) line emissions. The dust continuum emission showed a clear ring structure with inner and outer edges of ∼11 and ∼21 au, respectively. In addition, we detected an inner disk of <5 au radius enclosing the central star within the ring, the first observation of this structure. Thus, WL 17 has a ring–gap structure, not a ring–hole structure. We did not detect any marked emission in either the gap or inner disk, indicating that there is no sign of a planet, circumplanetary disk, or binary companion. We identified the source of both blueshifted and redshifted outflows based on the 12CO emission, which is clearly associated with the disk around WL 17. The outflow mass ejection rate is ∼3.6 × 10‑7 M ⊙ yr‑1 and the dynamical timescale is as short as ∼104 yr. The C18O emission showed that an inhomogeneous infalling envelope, which can induce episodic mass accretion, is distributed in the region within ∼1000 au from the central protostar. With these new findings, we can constrain the scenarios of planet formation and dust growth in the accretion phase of star formation.

DOI： 10.3847/1538-4357/ad12b5

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DOI： 10.1016/j.jnucmat.2023.154786

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DOI： 10.1051/0004-6361/202244692

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DOI： 10.1051/0004-6361/202244690

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Astrophysical Journal  

Abstract

We present the detection of a secondary outflow associated with a Class I source, Ser-emb 15, in the Serpens Molecular Cloud. We reveal two pairs of molecular outflows consisting of three lobes, that is, primary and secondary outflows, using Atacama Large Millimeter/submillimeter Array ¹²CO and SiO line observations at a resolution of ∼318 au. The secondary outflow is elongated approximately perpendicular to the axis of the primary outflow in the plane of the sky. We also identify two compact structures, Sources A and B, within an extended structure associated with Ser-emb 15 in the 1.3 mm continuum emission at a resolution of ∼40 au. The projected sizes of Sources A and B are 137 au and 60 au, respectively. Assuming a dust temperature of 20 K, we estimate the dust mass to be 2.4 × 10⁻³M_⊙ for Source A and 3.3 × 10⁻⁴M_⊙ for Source B. C¹⁸O line data imply rotational motion around the extended structure, but we cannot resolve rotational motion in Source A and/or B because the angular and frequency resolutions are insufficient. Therefore, we cannot conclude whether Ser-emb 15 is a single or binary system. Thus, either Source A or Source B could drive the secondary outflow. We discuss two scenarios that might explain the driving mechanism of the primary and secondary outflows: the Ser-emb 15 system is (1) a binary system composed of Sources A and B, or (2) a single-star system composed of Source A alone. In either case, the system could be a suitable target for investigating the disk and/or binary formation processes in complicated environments. Detecting these outflows should contribute to understanding complex star-forming environments, which may be common in the star formation processes.

DOI： 10.3847/1538-4357/ad0132

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その他リンク： https://iopscience.iop.org/article/10.3847/1538-4357/ad0132/pdf

記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Astrophysical Journal Letters  

Transferring a significant fraction of the magnetic flux from a dense cloud core is essential in the star formation process. A ringlike structure produced by magnetic flux loss has been predicted theoretically, but no observational identification has been presented. We have performed ALMA observations of the Class I protostar IRS 2 in the Corona Australis star-forming region and resolved a distinctive gas ring in the C18O (J = 2-1) line emission. The center of this gas ring is ∼5000 au away from the protostar, with a diameter of ∼7000 au. The radial velocity of the gas is ≲ 1 km s−1 blueshifted from that of the protostar, with a possible expanding feature judged from the velocity-field (moment 1) map and position-velocity diagram. These features are either observationally new or have been discovered but not discussed in depth because they are difficult to explain by well-studied protostellar phenomena such as molecular outflows and accretion streamers. A plausible interpretation is a magnetic wall created by the advection of magnetic flux, which is theoretically expected in the Class 0/I phase during star formation as a removal mechanism of magnetic flux. Similar structures reported in the other young stellar sources could likely be candidates formed by the same mechanism, encouraging us to revisit the issue of magnetic flux transport in the early stages of star formation from an observational perspective.

DOI： 10.3847/2041-8213/acfca9

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出版者・発行元：Progress of Theoretical and Experimental Physics  

The detections of gravitational waves (GW) by the LIGO/Virgo collaborations provide various possibilities for both physics and astronomy. We are quite sure that GW observations will develop a lot, both in precision and in number, thanks to the continuous work on the improvement of detectors, including the expected new detector, KAGRA, and the planned detector, LIGO-India. On this occasion, we review the fundamental outcomes and prospects of gravitational wave physics and astronomy. We survey the development, focusing on representative sources of gravitational waves: binary black holes, binary neutron stars, and supernovae. We also summarize the role of gravitational wave observations as a probe of new physics.

DOI： 10.1093/ptep/ptab042

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Astrophysical Journal  

Abstract

Recent millimeter/submillimeter facilities have revealed the physical properties of filamentary molecular clouds in relation to high-mass star formation. A uniform survey of the nearest, face-on star-forming galaxy, the Large Magellanic Cloud (LMC), complements the Galactic knowledge. We present ALMA survey data with a spatial resolution of ∼0.1 pc in the 0.87 mm continuum and HCO⁺ (4–3) emission toward 30 protostellar objects with luminosities of 10⁴–10^5.5L_⊙ in the LMC. The spatial distributions of the HCO⁺ (4–3) line and thermal dust emission are well correlated, indicating that the line effectively traces dense, filamentary gas with an H₂ volume density of ≳10⁵ cm⁻³ and a line mass of ∼10³–10⁴M_⊙ pc⁻¹. Furthermore, we obtain an increase in the velocity line widths of filamentary clouds, which follows a power-law dependence on their H₂ column densities with an exponent of ∼0.5. This trend is consistent with observations toward filamentary clouds in nearby star-forming regions within ≲1 kpc from us and suggests enhanced internal turbulence within the filaments due to surrounding gas accretion. Among the 30 sources, we find that 14 are associated with hub-filamentary structures, and these complex structures predominantly appear in protostellar luminosities exceeding ∼5 × 10⁴L_⊙. The hub-filament systems tend to appear in the latest stages of their natal cloud evolution, often linked to prominent H ii regions and numerous stellar clusters. Our preliminary statistics suggest that the massive filaments accompanied by hub-type complex features may be a necessary intermediate product in forming extremely luminous high-mass stellar systems capable of ultimately dispersing the parent cloud.

DOI： 10.3847/1538-4357/acefb7

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その他リンク： https://iopscience.iop.org/article/10.3847/1538-4357/acefb7/pdf

DOI： 10.3847/2041-8213/acdb60

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Publications of the Astronomical Society of Japan  

We propose a new evolutionary process for protoplanetary disks, the co-evolution of dust grains and protoplanetary disks, revealed by dust-gas two-fluid non-ideal magnetohydrodynamics simulations considering the growth of dust grains and associated changes in magnetic resistivity. We found that the dust growth significantly affects disk evolution by changing the coupling between the gas and the magnetic field. Moreover, once the dust grains grow sufficiently large and the adsorption of charged particles on to them becomes negligible, the physical quantities (e.g., density and magnetic field) of the disk are well described by characteristic power laws. In this disk structure, the radial profile of density is steeper and the disk mass is smaller than those of the model ignoring dust growth. We analytically derive these power laws from the basic equations of non-ideal magnetohydrodynamics. The analytical power laws are determined only by observable physical quantities, e.g., central stellar mass and mass accretion rate, and do not include difficult-to-determine parameters, e.g., the viscous parameter & alpha;. Therefore, our model is observationally testable and this disk structure is expected to provide a new perspective for future studies on protostar and disk evolution.

DOI： 10.1093/pasj/psad040

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Astrophysical Journal  

Abstract

Intermediate-mass black holes (with ≥10⁵M_⊙) are promising candidates for the origin of supermassive black holes (with ∼10⁹M_⊙) in the early universe (redshift z ∼ 6). Chon & Omukai first pointed out direct collapse black hole (DCBH) formation in metal-enriched atomic-cooling halos (ACHs), which relaxes the DCBH formation criterion. On the other hand, Hirano et al. showed that magnetic effects promote DCBH formation in metal-free ACHs. We perform a set of magnetohydrodynamical simulations to investigate star formation in magnetized ACHs with metallicities Z/Z_⊙ = 0, 10⁻⁵, and 10⁻⁴. Our simulations show that the mass accretion rate onto the protostars becomes lower in metal-enriched ACHs than in metal-free ACHs. However, many protostars form from gravitationally and thermally unstable metal-enriched gas clouds. Under such circumstances, the magnetic field rapidly increases as magnetic field lines wind up due to the spin of protostars. The region with the amplified magnetic field expands outwards due to the orbital motion of protostars and the rotation of the accreting gas. The amplified magnetic field extracts angular momentum from the accreting gas, promotes the coalescence of low-mass protostars, and increases the mass growth rate of the primary protostar. We conclude that the magnetic field amplification is always realized in metal-enriched ACHs regardless of the initial magnetic field strength, which affects the DCBH formation criterion. In addition, we find a qualitatively different trend from the previous unmagnetized simulations in that the mass growth rate is maximal for extremely metal-poor ACHs with Z/Z_⊙ = 10⁻⁵.

DOI： 10.3847/1538-4357/acda94

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その他リンク： https://iopscience.iop.org/article/10.3847/1538-4357/acda94/pdf

記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Monthly Notices of the Royal Astronomical Society  

We investigate the influence of dust particle size evolution on non-ideal magnetohydrodynamic (MHD) effects during the collapsing phase of star-forming cores, taking both the turbulence intensity in the collapsing cloud core and the fragmentation velocity of dust particles as parameters. When the turbulence intensity is small, the dust particles do not grow significantly, and the non-ideal MHD effects work efficiently in high-density regions. The dust particles rapidly grow in a strongly turbulent environment, while the efficiency of non-ideal MHD effects in such an environment depends on the fragmentation velocity of the dust particles. When the fragmentation velocity is small, turbulence promotes coagulation growth and collisional fragmentation of dust particles, producing small dust particles. In this case, the adsorption of charged particles on the dust particle surfaces becomes efficient and the abundance of charged particles decreases, making non-ideal MHD effects effective at high densities. On the other hand, when the fragmentation velocity is high, dust particles are less likely to fragment, even if the turbulence is strong. In this case, the production of small dust particles becomes inefficient and non-ideal MHD effects become less effective. We also investigate the effect of the dust composition on the star and disc formation processes. We constrain the turbulence intensity of a collapsing core and the fragmentation velocity of dust for circumstellar disc formation due to the dissipation of the magnetic field.

DOI： 10.1093/mnras/stad1241

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Monthly Notices of the Royal Astronomical Society  

We present results from the first molecular line survey to search for the fundamental complex organic molecule, methanol (CH3OH), in 14 Class 0/I proto-brown dwarfs (proto-BDs). IRAM 30-m observations over the frequency range of 92-116 and 213-280 GHz have revealed emission in 14 CH3OH transition lines, at upper state energy level, Eupper ∼7-49 K, and critical densities, ncrit of 105-109 cm−3. The most commonly detected lines are at Eupper < 20 K, while 11 proto-BDs also show emission in the higher excitation lines at Eupper ∼21-49 K and ncrit ∼ 105 to 108 cm−3. In comparison with the brown dwarf formation models, the high excitation lines likely probe the warm (∼25-50 K) corino region at ∼10-50 au in the proto-BDs, while the low-excitation lines trace the cold (<20 K) gas at ∼50-150 au. The column density for the cold component is an order of magnitude higher than the warm component. The CH3OH ortho-to-para ratios range between ∼0.3 and 2.3. The volume-averaged CH3OH column densities show a rise with decreasing bolometric luminosity among the proto-BDs, with the median column density higher by a factor of ∼3 compared to low-mass protostars. Emission in high-excitation (Eupper > 25 K) CH3OH lines together with the model predictions suggest that a warm corino is present in ∼78 per cent of the proto-BDs in our sample. The remaining shows evidence of only the cold component, possibly due to the absence of a strong, high-velocity jet that can stir up the warm gas around it.

DOI： 10.1093/mnras/stad1329

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Astronomical Journal  

The Subaru telescope is currently performing a strategic program (SSP) using the high-precision near-infrared (NIR) spectrometer IRD to search for exoplanets around nearby mid/late M dwarfs via radial velocity (RV) monitoring. As part of the observing strategy for the exoplanet survey, signatures of massive companions such as RV trends are used to reduce the priority of those stars. However, this RV information remains useful for studying the stellar multiplicity of nearby M dwarfs. To search for companions around such "deprioritized" M dwarfs, we observed 14 IRD-SSP targets using Keck/NIRC2 with pyramid wave-front sensing at NIR wavelengths, leading to high sensitivity to substellar-mass companions within a few arcseconds. We detected two new companions (LSPM J1002+1459 B and LSPM J2204+1505 B) and two new candidates that are likely companions (LSPM J0825+6902 B and LSPM J1645+0444 B), as well as one known companion. Including two known companions resolved by the IRD fiber injection module camera, we detected seven (four new) companions at projected separations between similar to 2 and 20 au in total. A comparison of the colors with the spectral library suggests that LSPM J2204+1505 B and LSPM J0825+6902 B are located at the boundary between late M and early L spectral types. Our deep high-contrast imaging for targets where no bright companions were resolved did not reveal any additional companion candidates. The NIRC2 detection limits could constrain potential substellar-mass companions (similar to 10-75 M (Jup)) at 10 au or further. The failure with Keck/NIRC2 around the IRD-SSP stars having significant RV trends makes these objects promising targets for further RV monitoring or deeper imaging with the James Webb Space Telescope to search for smaller-mass companions below the NIRC2 detection limits.

DOI： 10.3847/1538-3881/acbf37

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Astrophysical Journal  

Abstract

We report on an Atacama Large Millimeter/submillimeter Array study of the Class I or II intermediate-mass protostar DK Cha in the Chamaeleon II region. The ¹²CO(J = 2–1) images have an angular resolution of ∼1″ (∼250 au) and show high-velocity blueshifted (≳70 km s⁻¹) and redshifted (≳50 km s⁻¹) emissions, which have 3000 au scale crescent-shaped structures around the protostellar disk traced in the 1.3 mm continuum. Because the high-velocity components of the CO emission are associated with the protostar, we concluded that the emission traces the pole-on outflow. The blueshifted outflow lobe has a clear layered velocity gradient with a higher-velocity component located on the inner side of the crescent shape, which can be explained by a model of an outflow with a higher velocity in the inner radii. Based on the directly driven outflow scenario, we estimated the driving radii from the observed outflow velocities and found that the driving region extends over 2 orders of magnitude. The ¹³CO emission traces a complex envelope structure with arc-like substructures with lengths of ∼1000 au. We identified the arc-like structures as streamers because they appear to be connected to a rotating infalling envelope. DK Cha is useful for understanding characteristics that are visible by looking at nearly face-on configurations of young protostellar systems, providing an alternative perspective for studying the star formation process.

DOI： 10.3847/1538-4357/acb930

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その他リンク： https://iopscience.iop.org/article/10.3847/1538-4357/acb930/pdf

記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Monthly Notices of the Royal Astronomical Society  

We calculate the evolution of cloud cores embedded in different envelopes to investigate environmental effects on the mass accretion rate on to protostars. As the initial state, we neglect the magnetic field and cloud rotation, and adopt star-forming cores composed of two parts: a centrally condensed core and an outer envelope. The inner core has a critical Bonnor-Ebert density profile and is enclosed by the outer envelope. We prepare 15 star-forming cores with different outer envelope densities and gravitational radii, within which the gas flows into the collapsing core, and calculate their evolution until ∼2 × 105 yr after protostar formation. The mass accretion rate decreases as the core is depleted when the outer envelope density is low. In contrast, the mass accretion rate is temporarily enhanced when the outer envelope density is high and the resultant protostellar mass exceeds the initial mass of the centrally condensed core. Some recent observations indicate that the mass of pre-stellar cores is too small to reproduce the stellar mass distribution. Our simulations show that the mass inflow from outside the core contributes greatly to protostellar mass growth when the core is embedded in a high-density envelope, which could explain the recent observations.

DOI： 10.1093/mnras/stac3819

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DOI： 10.1093/pasj/psac045

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DOI： 10.1093/pasj/psac103

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Astrophysical Journal  

Abstract

We present a high-angular resolution (∼1″) and wide-field ($2uildrel{,prime}over{.} 9 imes 1uildrel{,prime}over{.} 9$) image of the 1.3 mm continuum, CO(J = 2–1) and SiO(J = 5–4) line emissions toward an embedded protocluster, FIR 3, FIR 4, and FIR 5, in the Orion Molecular Cloud 2 obtained from the Atacama Large Millimeter/submillimeter Array. We identify 51 continuum sources, 36 of which are newly identified in this study. Their dust masses, projected sizes, and H₂ gas number densities are estimated to be 3.8 × 10⁻⁵–1.1 × 10⁻²M_⊙, 290–2000 au, and 6.4 × 10⁶–3.3 × 10⁸ cm⁻³, respectively. The results of a Jeans analysis show that ∼80% of the protostellar sources and ∼15% of the prestellar sources are gravitationally bound. We identify 12 molecular outflows traced in the CO(J = 2–1) emission, six of which are newly detected. We spatially resolve shocked gas structures traced by the SiO(J = 5–4) emission in this region for the first time. We identify shocked gas originating from outflows and other shocked regions. These results provide direct evidence of an interaction between dust condensation, FIR 4, and an energetic outflow driven by HOPS-370 located within FIR 3. A comparison of the outflow dynamical timescales, fragmentation timescales, and protostellar ages shows that the previously proposed triggered star formation scenario in FIR 4 is not strongly supported. We also discuss the spatial distribution of filaments identified in our continuum image by comparing it with a previously identified hub-fiber system in the N₂H⁺ line.

DOI： 10.3847/1538-4357/aca7c9

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その他リンク： https://iopscience.iop.org/article/10.3847/1538-4357/aca7c9/pdf

出版者・発行元：Monthly Notices of the Royal Astronomical Society  

We calculate the evolution of a star-forming cloud core using a three-dimensional resistive magnetohydrodynamics simulation, treating dust grains as Lagrangian particles, to investigate the dust motion in the early star formation stage. We prepare six different-sized set of dust particles in the range ad = 0.01-1000 μm, where ad is the dust grain size. In a gravitationally collapsing cloud, a circumstellar disk forms around a protostar and drives a protostellar outflow. Almost all the small dust grains (ad 10-100 μm) initially distributed in the region θ0 45° are ejected from the center by the outflow, where θ0 is the initial zenith angle relative to the rotation axis, whereas only a small number of the large dust grains (a d gtrsim 100 μm) distributed in the region are ejected. All other grains fall onto either the protostar or disk without being ejected by the outflow. Regardless of the dust grain size, the behavior of the dust motion is divided into two trends after dust particles settle into the circumstellar disk. The dust grains reaching the inner disk region from the upper envelope preferentially fall onto the protostar, while those reaching the outer disk region or disk outer edge from the envelope can survive without an inward radial drift. These surviving grains can induce dust growth. Thus, we expect that the outer disk regions could be a favored place of planet formation.

DOI： 10.1093/mnras/stac3503

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Proceedings of the International Astronomical Union  

We report on a direct comparison of VLBI maser data and ALMA thermal-emission data for the high-mass protostar G353.273+0.641. We detected a gravitationally-unstable disk by dust and a high-velocity jet traced by a thermal CO line by ALMA long-baselines (LB). 6.7 GHz CH3OH masers trace infalling streamlines inside the disk. The innermost maser ring indicates another compact accretion disk of 30 au. Such a nested system could be caused by angular momentum transfer by the spiral arms. 22 GHz H2O masers trace the jet-accelerating region, which are directly connecting the CO jet and the protostar. The recurrent maser flares imply episodic jet ejections per 1–2 yr, while typical separation of CO knots indicates a variation of outflow rate per 100 yr. Our study demonstrates that VLBI maser observations are still a powerful tool to explore detailed structures nearby high-mass protostars by combining ALMA LB.

DOI： 10.1017/s1743921323003216

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Publications of the Astronomical Society of Japan  

Understanding the initial conditions of star formation requires both
observational studies and theoretical works taking into account the magnetic
field, which plays an important role in star formation processes. Herein, we
study the young nearby dense cloud core L1521 F ($n$(H$_2$) $sim 10^{4-6}$
cm$^{-3}$) in the Taurus Molecular Cloud. This dense core hosts a 0.2 $M_odot$
protostar, categorized as a Very Low Luminosity Objects with complex velocity
structures, particularly in the vicinity of the protostar. To trace the
magnetic field within the dense core, we conducted high sensitivity
submillimeter polarimetry of the dust continuum at $lambda$= 850 $mu$m and
450 $mu$m using the POL-2 polarimeter situated in front of the SCUBA-2
submillimeter bolometer camera on James Clerk Maxwell Tetescope. This was
compared with millimeter polarimetry taken at $lambda$= 3.3 mm with ALMA. The
magnetic field was detected at $lambda$= 850 $mu$m in the peripheral region,
which is threaded in a north-south direction, while the central region traced
at $lambda$= 450 $mu$m shows a magnetic field with an east-west direction,
i.e., orthogonal to that of the peripheral region. Magnetic field strengths are
estimated to be $sim$70 $mu$G and 200 $mu$G in the peripheral- and
central-regions, respectively, using the Davis-Chandrasekhar-Fermi method. The
resulting mass-to-flux ratio of 3 times larger than that of magnetically
critical state for both regions indicates that L1521 F is magnetically
supercritical, i.e., gravitational forces dominate over magnetic turbulence
forces. Combining observational data with MHD simulations, detailed parameters
of the morphological properties of this puzzling object are derived for the
first time.

DOI： 10.1093/pasj/psac094

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その他リンク： http://arxiv.org/pdf/2211.08988v1

記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Monthly Notices of the Royal Astronomical Society  

The aim of this study is to examine dust dynamics on a large scale and investigate the coupling of dust with gas fluid in the star formation process. We propose a method for calculating the dust trajectory in a gravitationally collapsing cloud, where the dust grains are treated as Lagrangian particles and are assumed to be neutral. We perform the dust trajectory calculations in combination with non-ideal magnetohydrodynamics simulation. Our simulation shows that dust particles with a size of $le 10, {
m mu m}$ are coupled with gas in a star-forming cloud core. We investigate the time evolution of the dust-to-gas mass ratio and the Stokes number, which is defined as the stopping time normalized by the freefall time-scale, and show that large dust grains ($gtrsim 100, {
m mu m}$) have a large Stokes number (close to unity) and tend to concentrate in the central region (i.e. protostar and rotationally supported disc) faster than do small grains ($lesssim 10, {
m mu m}$). Thus, large grains significantly increase the dust-to-gas mass ratio around and inside the disc. We also confirm that the dust trajectory calculations, which trace the physical quantities of each dust particle, reproduce previously reported results obtained using the Eulerian approach.

DOI： 10.1093/mnras/stac2115

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Astrophysical Journal Letters  

Abstract

Protostellar outflows are one of the most outstanding features of star formation. Observational studies over the last several decades have successfully demonstrated that outflows are ubiquitously associated with low- and high-mass protostars in solar-metallicity Galactic conditions. However, the environmental dependence of protostellar outflow properties is still poorly understood, particularly in the low-metallicity regime. Here we report the first detection of a molecular outflow in the Small Magellanic Cloud with 0.2 Z_⊙, using Atacama Large Millimeter/submillimeter Array observations at a spatial resolution of 0.1 pc toward the massive protostar Y246. The bipolar outflow is nicely illustrated by high-velocity wings of CO(3–2) emission at ≳15 km s⁻¹. The evaluated properties of the outflow (momentum, mechanical force, etc.) are consistent with those of the Galactic counterparts. Our results suggest that the molecular outflows, i.e., the guidepost of the disk accretion at the small scale, might be universally associated with protostars across the metallicity range of ∼0.2–1 Z_⊙.

DOI： 10.3847/2041-8213/ac81c1

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その他リンク： https://iopscience.iop.org/article/10.3847/2041-8213/ac81c1/pdf

記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Astrophysical Journal  

The canonical theory of star formation in a magnetized environment predicts the formation of hourglass-shaped magnetic fields during the prestellar collapse phase. In protostellar cores, recent observations reveal complex and strongly distorted magnetic fields in the inner regions that are sculpted by rotation and outflows. We conduct resistive, nonideal magnetohydrodynamic simulations of a protostellar core and employ the radiative transfer code POLARIS to produce synthetic polarization segment maps. A comparison of our mock-polarization maps based on the toroidal-dominated magnetic field in the outflow zone with the observed polarization vectors of SiO lines in Orion Source I shows a reasonable agreement when the magnetic axis is tilted at an angle θ = 15° with respect to the plane of the sky and if the SiO lines have a net polarization parallel to the local magnetic field. Although the observed polarization is from SiO lines and our synthetic maps are due to polarized dust emission, a comparison is useful and allows us to resolve the ambiguity of whether the line polarization is parallel or perpendicular to the local magnetic field direction.

DOI： 10.3847/1538-4357/ac7c0f

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Monthly Notices of the Royal Astronomical Society  

We determine the time-evolution of the dust particle size distribution during the collapse of a cloud core, accounting for both dust coagulation and dust fragmentation, to investigate the influence of dust growth on non-ideal magnetohydrodynamic (MHD) effects. The density evolution of the collapsing core is given by a one-zone model. We assume two types of dust model: dust composed only of silicate (silicate dust) and dust with a surface covered by H2O ice (H2O ice dust). When only considering collisional coagulation, the non-ideal MHD effects are not effective in the high-density region for both the silicate and H2O ice dust cases. This is because dust coagulation reduces the abundance of small dust particles, resulting in less efficient adsorption of charged particles on the dust surface. For the silicate dust case, when collisional fragmentation is included, the non-ideal MHD effects do apply at a high density of nH > 1012 cm-3 because of the abundant production of small dust particles. On the other hand, for the H2O ice dust case, the production of small dust particles due to fragmentation is not efficient. Therefore, for the H2O ice dust case, non-ideal magnetohydrodynamic effects apply only in the range nH ≳ 1014 cm-3, even when collisional fragmentation is considered. Our results suggest that it is necessary to consider both dust collisional coagulation and fragmentation to activate non-ideal magnetohydrodynamic effects, which should play a significant role in the star and disc formation processes.

DOI： 10.1093/mnras/stac1919

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Astrophysical Journal  

Abstract

Gas accretion onto the circumplanetary disks and the source region of accreting gas are important to reveal dust accretion that leads to satellite formation around giant planets. We performed local three-dimensional high-resolution hydrodynamic simulations of an isothermal and inviscid gas flow around a planet to investigate the planetary-mass dependence of the gas accretion bandwidth and gas accretion rate onto circumplanetary disks. We examined cases with various planetary masses corresponding to M_p = 0.05–1M_Jup at 5.2 au, where M_Jup is the current Jovian mass. We found that the radial width of the gas accretion band is proportional to ${M}_{ {
m{p } } }^{1/6}$ for the low-mass regime with M_p ≲ 0.2M_Jup while it is proportional to M_p for the high-mass regime with M_p ≳ 0.2M_Jup. We found that the ratio of the mass accretion rate onto the circumplanetary disk to that into the Hill sphere is about 0.4 regardless of the planetary mass for the cases we examined. Combining our results with the gap model obtained from global hydrodynamic simulations, we derive a semi-analytical formula of mass accretion rate onto circumplanetary disks. We found that the mass dependence of our three-dimensional accretion rates is the same as the previously obtained two-dimensional case, although the qualitative behavior of accretion flow onto the circumplanetary disk is quite different between the two cases.

DOI： 10.3847/1538-4357/ac7ddf

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その他リンク： https://iopscience.iop.org/article/10.3847/1538-4357/ac7ddf/pdf

記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Astrophysical Journal Letters  

Abstract One critical remaining issue that is unclear in the initial mass function of the first (Population III) stars is the final fate of secondary protostars that formed in the accretion disk—specifically, whether they merge or survive. We focus on the magnetic effects on the formation of the first star under a cosmological magnetic field. We perform a suite of ideal magnetohydrodynamic simulations for 1000 yr after the first protostar formation. Instead of the sink particle technique, we employ a stiff equation of state approach to represent the magnetic field structure connecting protostars. Ten years after the first protostar formation in the cloud initialized with B₀ = 10⁻²⁰ G at n₀ = 10⁴ cm⁻³, the magnetic field strength around the protostars has amplified from pico- to kilo-Gauss, which is the same strength as the present-day star. The magnetic field rapidly winds up since the gas in the vicinity of the protostar (≤10 au) has undergone several tens of orbital rotations in the first decade after protostar formation. As the mass accretion progresses, the vital magnetic field region extends outward, and magnetic braking eliminates the fragmentation of the disk that would happen in an unmagnetized model. On the other hand, assuming a gas cloud with a small angular momentum, this amplification might not work because the rotation would be slower. However, disk fragmentation would not occur in that case. We conclude that the exponential amplification of the cosmological magnetic field strength, about 10⁻¹⁸ G, eliminates disk fragmentation around Population III protostars.

DOI： 10.3847/2041-8213/ac85e0

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その他リンク： https://iopscience.iop.org/article/10.3847/2041-8213/ac85e0/pdf

DOI： 10.1021/acs.jpcc.1c08739

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Astronomical Journal  

Detailed chemical analyses of M dwarfs are scarce but necessary to constrain the formation environment and internal structure of planets being found around them. We present elemental abundances of 13 M dwarfs (2900 < T (eff) < 3500 K) observed in the Subaru/IRD planet search project. They are mid- to late-M dwarfs whose abundance of individual elements has not been well studied. We use the high-resolution (similar to 70,000) near-infrared (970-1750 nm) spectra to measure the abundances of Na, Mg, Si, K, Ca, Ti, V, Cr, Mn, Fe, and Sr by the line-by-line analysis based on model atmospheres, with typical errors ranging from 0.2 dex for [Fe/H] to 0.3-0.4 dex for other [X/H]. We measure radial velocities from the spectra and combine them with Gaia astrometry to calculate the Galactocentric space velocities UVW. The resulting [Fe/H] values agree with previous estimates based on medium-resolution K-band spectroscopy, showing a wide distribution of metallicity (-0.6 < [Fe/H] < +0.4). The abundance ratios of individual elements [X/Fe] are generally aligned with the solar values in all targets. While the [X/Fe] distributions are comparable to those of nearby FGK stars, most of which belong to the thin-disk population, the most metal-poor object, GJ 699, could be a thick-disk star. The UVW velocities also support this. The results raise the prospect that near-infrared spectra of M dwarfs obtained in the planet search projects can be used to grasp the trend of elemental abundances and the Galactic stellar population of nearby M dwarfs.

DOI： 10.3847/1538-3881/ac3ee0

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出版者・発行元：arXiv  

We present our current understanding of the formation and early evolution of protostars, protoplanetary disks, and the driving of outflows as dictated by the interplay of magnetic fields and partially ionized gas in molecular cloud cores. In recent years, the field has witnessed enormous development through sub-millimeter observations which in turn have constrained models of protostar formation. As a result of these observations % that the observations provided, the state-of-the-art theoretical understanding of the formation and evolution of young stellar objects is described. In particular, we emphasize the importance of the coupling, decoupling, and re-coupling between weakly ionized gas and the magnetic field on appropriate scales. This highlights the complex and intimate relationship between gravitational collapse and magnetic fields in young protostars.

DOI： 10.48550/ARXIV.2209.13765

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記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/2041-8213/ac2b2f

記述言語：その他  

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/mnras/stab2626

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/abfdbb

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/ac0913

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/ac069f

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/abf5db

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/abb810

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/abe61c

記述言語：その他  

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/abc6fc

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/abbc08

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/2041-8213/ab9ca8

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/ab9ca7

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/ab9f9d

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/2041-8213/ab9d86

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/ab93d0

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/ab959e

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/ab8065

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/ab8065

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/mnras/stz3159

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/ab5284

記述言語：その他  

Driving conditions of protostellar outflows in different star-forming environments

DOI： 10.1093/mnras/stz1079

記述言語：その他  

Origin of misalignments: protostellar jet, outflow, circumstellar disc, and magnetic field

DOI： 10.1093/mnras/stz740

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/aaf1b6

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/mnras/stz1032

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/aae4dc

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/aae153

記述言語：その他  

Evolution of magnetic fields in collapsing star-forming clouds under different environments

DOI： 10.1093/mnras/sty046

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/mnras/stx3070

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/mnras/stx2589

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/2041-8213/aa9701

記述言語：その他   掲載種別：研究論文（学術雑誌）  

ALMA observations of submillimeter H2O and SiO lines in Orion Source I
We present observational results of the submillimeter H2O and SiO lines<br />
toward a candidate high-mass young stellar object Orion Source I using ALMA.<br />
The spatial structures of the high excitation lines at lower-state energies of<br />
>2500 K show compact structures consistent with the circumstellar disk and/or<br />
base of the northeast-southwest bipolar outflow with a 100 au scale. The<br />
highest excitation transition, the SiO (v=4) line at band 8, has the most<br />
compact structure. In contrast, lower-excitation transitions are more extended<br />
than 200 au tracing the outflow. Almost all the line show velocity gradients<br />
perpendicular to the outflow axis suggesting rotation motions of the<br />
circumstellar disk and outflow. While some of the detected lines show broad<br />
line profiles and spatially extended emission components indicative of thermal<br />
excitation, the strong H2O lines at 321 GHz, 474 GHz, and 658 GHz with<br />
brightness temperatures of >1000 K show clear signatures of maser action.

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/aa8e9e

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/aa8264

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/mnras/stx893

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1038/s41550-017-0146

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/aa6a1c

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/836/1/148

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/2041-8213/835/1/L11

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/mnras/stw2256

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/833/2/238

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/0004-637X/826/1/26

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0004-637X/812/1/27

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/2041-8205/810/2/L26

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/mnras/stu2633

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0004-637X/801/2/117

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0004-637X/796/2/131

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/2041-8205/796/1/L17

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0004-637X/793/1/1

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/2041-8205/789/1/L4

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0004-637X/784/2/109

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/mnras/stt2343

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/mnras/stt1684

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0004-637X/770/1/71

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/mnras/sts111

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0004-637X/763/1/6

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0004-637X/761/1/40

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/2041-8205/750/2/L29

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0004-637X/747/1/47

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1111/j.1365-2966.2011.20336.x

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1111/j.1365-2966.2011.19081.x

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/pasj/63.3.555

記述言語：英語  

DOI： 10.1088/2041-8205/732/1/L18

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0004-637X/729/1/42

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DOI： 10.1088/2041-8205/725/2/L239

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0004-637X/724/2/1006

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/2041-8205/718/2/L58

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1111/j.1365-2966.2010.16527.x

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/2041-8205/714/1/L58

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1111/j.1365-2966.2009.15394.x

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0004-637X/703/1/1141

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0004-637X/699/2/L157

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1086/590421

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1086/591074

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1086/590109

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1086/587027

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1086/533434

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1086/528364

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1086/529133

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1086/521779

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1017/S1743921308016906

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1086/504423

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

DOI： 10.1016/j.cpc.2004.06.033

開催年月日： 2012年9月

記述言語：日本語   会議種別：口頭発表（一般）  

開催地：大分大学   国名：日本国  

初代星の形成・進化を理解することは宇宙の進化を理解する上で重要である。 過去の研究から、一つのダークマターハロー中では単一の大質量初代星 が形成されると考えられてきた。 しかし、過去の研究は球対称を仮定していたために、角運動量の 効果を無視していた。その後の3次元シミュレーションも初代星形成直 後までしか計算していなかったために、初代星形成後の円盤形成段階は 調べられていなかった。 近年、シンクセル法などを用いて複数のグループが初代星形成後の進化 の計算を行った。これらの研究は、原始星誕生後に周囲の円盤が分裂して 複数の星が形成しうることを示した。 しかし、これらの計算では、(i)シンクセルが大きすぎるために分裂が盛ん に起こるであろう円盤の内側領域を計算出来ない、または、 (ii)シンクセルを用いない場合には原始星の内部構造まで計算して しまうために長時間計算が出来ないという問題があった。 この研究では、シンクセルを用いずに原始星形成後の長時間 計算を実現した。具体的には、過去の初代星の進化計算から得られた質量と 半径の関係をガスの状態方程式に組み込んだ。この手法により中心星 は質量の増加と共に半径を増大させる。そのため原始星の内部構造を計算 することは出来ないが、原始星周囲の構造を長時間計算することが可能である。 計算の結果、磁場が無い場合には、他の計算で示されているように 激しく分裂が起こり、多数の星が誕生することが分かった。 いくつかの原始星は中心近傍の比較的質量の大きな星に落下する。また、いくつかの 原始星は中心部から放出される。放出される星の最小質量は木星質量程度で ある。他方、初期宇宙に非常に弱い磁場が存在する場合には、磁気制動によって 角運動量が輸送され星周円盤が成長しない。そのため、古典的 描像のようにダークマターハローの中心に単一の大質量星が誕生する。

開催年月日： 2012年3月

会議種別：口頭発表（一般）  

開催地：龍谷大学   国名：日本国  

星や円盤形成の母体となる分子雲は、磁化されておりマイクロガウス程度 の磁場を保持している。星や円盤は、この磁気星間雲 が重力収縮して形成する。星周円盤は、惑星形成の母体でもあるため、 その形成過程を理解することは星形成のみならず惑星形成の観点からも 重要である。 近年、この重力収縮するガス雲中での円盤の形成について「Magnetic Braking Catastrophe」という困難があると指摘されている。 これは、重力収縮の過程、または星形成後のガス降着段階で、磁場の効果 により角運動量が輸送されてしまい回転円盤が出来ないという問題であ る。 円盤が形成するとその回転によって磁力線が強く捻られる。 すると円盤の角運動量は、この磁力線を捻ることによって星間空間に輸送される。 円盤が回転を続ける限り磁力線が捻られ続け角運動量も輸送され続ける。 そのため、星形成過程では回転円盤が出来ないという主張である。 我々は、磁気星間雲中での星周円盤の形成過程を調べるために、磁気散逸 MHD多層格子法を用いて、星形成前の分子雲コアから星が誕生して円盤が 出来る過程の計算を行った。その結果、分子雲の磁場が強い場合でも回転円盤が 出来ることが分かった。円盤形成の初期段階では、周囲に十分なガスが 残っているために、円盤の角運動量は磁力線を通じて円盤周囲のガス に輸送される。しかし、分子雲が十分進化して、分子雲内のガスが円盤に落下し 円盤ガスよりも軽くなると角運動量を効率的に輸送できなくなる。従って、 分子雲のガスが枯渇しつつある段階では回転円盤の形成が可能となる。 さらに、初期にガス雲が重力的に非常に不安定であり円盤へのガス降着率が 大きい場合には、磁場による角運動量輸送率よりもガス降着によって持ち込 まれる角運動量の方が大きくなり、中心星が非常に若い段階でも十分に大き く重い円盤が出来ることが分かった。

開催年月日： 2011年9月

会議種別：口頭発表（一般）  

開催地：鹿児島大学   国名：日本国  

系外惑星の観測は、主星の重元素量が多い程、惑星が存在する確率が高いこと を示している。 コア・アクリーションシナリオに従うと、このような 重元素量が多い円盤中では固体コアが出来やすくガス惑星も誕生しやす いことが分かる。そのため、主星の重元素量と惑星頻度の関係は、 惑星がコア・アクリーションによって誕生したことの間接的な証拠であると 考えられている。 他方、もう一つの惑星形成シナリオである重力不安定シナリオでは、ダスト や重元素量の違いは、ガス惑星の形成にはほとんど影響を与えないと考えられ ている。しかし、この重力不安定シナリオを考える場合には、円盤の形成も 考慮する必要がある。 この講演では、円盤のサイズや質量がダストの量(重元素量)と密接に関係しており、 コア・アクリーションシナリオと同様に、金属量が高いほど重い円盤が形成し、 重力不安定によりガス惑星形成が誕生しやすいことを示す。 観測されているような分子雲コアを初期条件として、ガスに含まれるダストの量 をパラメータとして、円盤形成の計算を行った。ダストの存在量の違いは、ガス の熱進化とイオン化度を通して磁場の散逸に影響を与える。計算の結果、ダスト の量が多いほど、重くサイズの大きな円盤が出来ることが分かった。これは、 以下の2つの理由による。 (1)ダスト量が多い程、ガスが光学的に厚くなる密度が低く、初期により大きな円盤 を形成する。 (2)ガス中にダストが豊富に存在する程、ガスのイオン化度が低く 磁場がより散逸して磁場制動 による角運動量輸送が非効率的になり大きな円盤を成長させる。 これらの結果は、星形成前の分子雲コアが重元素を豊富に含むほど、重力不安定 によってガス惑星 が誕生しやすいことを示唆している。

開催年月日： 2011年3月

会議種別：口頭発表（一般）  

開催地：筑波大学   国名：日本国  

その他リンク： http://www.asj.or.jp/nenkai/2011a/

開催年月日： 2010年9月

会議種別：口頭発表（一般）  

開催地：金沢大学   国名：日本国  

その他リンク： http://www.asj.or.jp/nenkai/2010b/

開催年月日： 2010年3月

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開催地：広島大学   国名：日本国  

その他リンク： http://www.asj.or.jp/nenkai/2010a/

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その他リンク： http://www.asj.or.jp/nenkai/2003a/

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