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 developed a one-dimensional magnetohydrodynamic (MHD) simulation code to investigate the long-term evolution of protoplanetary disks with low computational cost. In this simulation code, the physical processes necessary for protostellar formation and protoplanetary disk evolution, such as magnetic braking, nonideal MHD effects, and angular momentum transport due to viscosity, are implemented. Using this simulation code, we performed the simulations of the long-term evolution of protoplanetary disks starting from the molecular cloud. Our simulation results suggest that the disk size and mass are a few tens of astronomical units and ∼0.01 M<inf>⊙</inf> at 10⁵ yr after protostellar formation. These values were relatively consistent with observations. The disk evolves through magnetic braking, and its radial profiles are consistent with the analytical solutions of previous studies. Our simulation code will be an important tool for studying the long-term evolution of protoplanetary disks.

DOI： 10.3847/1538-4357/adf4ea

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その他リンク： https://iopscience.iop.org/article/10.3847/1538-4357/adf4ea/pdf

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  

In this study, we perform 3D magnetohydrodynamics (MHD) simulations of filamentary molecular clouds. We then generate synthetic observations based on the simulation results. Using these, we investigate how the new polarization data analysis method recently introduced by Doi et al. (2021, ApJ, 923, L9) reflects the magnetic field structure in turbulent filamentary molecular clouds. Doi et al. proposed that the R<inf>FWHM</inf>, the ratio of the full width at half maximum (FWHM) of the polarized intensity (PI) to that of the total intensity (I) can be used to probe the three-dimensional structure of the magnetic field. We calculate the R<inf>FWHM</inf> from the density and magnetic field structure obtained in the 3D-MHD simulations. We find that the mean and variance of R<inf>FWHM</inf> within a filament are smaller and larger, respectively, with a larger inclination of the magnetic field to the plane-of-sky. We also find that both small-scale (<0.1 pc) and large-scale (≳0.1 pc) turbulence affect the polarized intensity of the dust thermal emission. We conclude that future extensive observations of R<inf>FWHM</inf> may be able to quantify the inclination of the magnetic field to the plane-of-sky in the filamentary molecular clouds.

DOI： 10.1093/pasj/psae115

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担当区分：筆頭著者   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  

Observed protostellar outflows exhibit a variety of asymmetrical features, including remarkable unipolar outflows and bending outflows. Revealing the formation and early evolution of such asymmetrical protostellar outflows, especially the unipolar outflows, is essential for a better understanding of the star and planet formation because they can dramatically change the mass accretion and angular momentum transport to the protostars and protoplanetary disks. Here we perform three-dimensional nonideal magnetohydrodynamics simulations to investigate the formation and early evolution of the asymmetrical protostellar outflows in magnetized turbulent isolated molecular cloud cores. We find, for the first time to our knowledge, that the unipolar outflow forms even in the single low-mass protostellar system. The results show that the unipolar outflow is driven in the weakly magnetized cloud cores with the dimensionless mass-to-flux ratios of μ = 8 and 16. Furthermore, we find the protostellar rocket effect of the unipolar outflow, which is similar to the launch and propulsion of a rocket. The unipolar outflow ejects the protostellar system from the central dense region to the outer region of the parent cloud core, and the ram pressure caused by its ejection suppresses the driving of additional new outflows. In contrast, the bending bipolar outflow is driven in the moderately magnetized cloud core with μ = 4. The ratio of the magnetic to turbulent energies of a parent cloud core may play a key role in the formation of asymmetrical protostellar outflows.

DOI： 10.3847/1538-4357/ad187a

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その他リンク： https://iopscience.iop.org/article/10.3847/1538-4357/ad187a/pdf

記述言語：英語   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 study the formation and early evolution of young stellar objects (YSOs) using three-dimensional non-ideal magnetohydrodynamic (MHD) simulations to investigate the effect of cosmic ray ionization rate and dust fraction (or amount of dust grains) on circumstellar disc formation. Our simulations show that a higher cosmic ray ionization rate and a lower dust fraction lead to (i) a smaller magnetic resistivity of ambipolar diffusion, (ii) a smaller disc size and mass, and (iii) an earlier timing of outflow formation and a greater angular momentum of the outflow. In particular, at a high cosmic ray ionization rate, the discs formed early in the simulation are dispersed by magnetic braking on a time-scale of about 104 yr. Our results suggest that the cosmic ray ionization rate has particularly a large impact on the formation and evolution of discs, while the impact of the dust fraction is not significant.

DOI： 10.1093/mnras/stad711

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その他リンク： https://academic.oup.com/mnras/article-pdf/521/2/2661/49570672/stad711.pdf

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 report our analyses of the multi-epoch (2015-2017) Atacama Large Millimeter/submillimeter Array (ALMA) archival data of the Class II binary system XZ Tau at Bands 3, 4, and 6. The millimeter dust-continuum images show compact, unresolved (r 15 au) circumstellar disks (CSDs) around the individual binary stars, XZ Tau A and B, with a projected separation of ∼39 au. The 12CO (2-1) emission associated with those CSDs traces the Keplerian rotations, whose rotational axes are misaligned with each other (P.A. ∼-5° for XZ Tau A and ∼130° for XZ Tau B). The similar systemic velocities of the two CSDs (VLSR ∼ 6.0 km s-1) suggest that the orbital plane of the binary stars is close to the plane of the sky. From the multi-epoch ALMA data, we have also identified the relative orbital motion of the binary. Along with the previous NIR data, we found that the elliptical orbit (e = - 0.742+0.034 0.025, = a 0. 172+0. 003 0. 002, and w = -54 .2+ 4 .7 2.0) is preferable to the circular orbit. Our results suggest that the two CSDs and the orbital plane of the XZ Tau system are all misaligned with each other, and possible mechanisms to produce such a configuration are discussed. Our analyses of the multi-epoch ALMA archival data demonstrate the feasibility of time-domain science with ALMA.

DOI： 10.3847/1538-4357/ac0dc3

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