Faculty Profiles - TSUKAMOTO Yusuke

Papers - TSUKAMOTO Yusuke

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Uchimura H., Kudoh T., Tsukamoto Y. . “Ashfall” Induced by Molecular Outflow in Protostar Evolution. II. Analytical Study on the Maximum Size of Dust Grains Lifted by Outflows . Astrophysical Journal984 ( 2 ) 2025.5Reviewed

Language：Japanese Publisher：Astrophysical Journal

In this paper, we study the dust dynamics in the molecular outflow using an analytical magnetohydrodynamical outflow model. Specifically, we investigate the maximum size of dust grains a d ,max that can be lifted by the outflow and whether they can escape into interstellar space. We also investigate the dependence of the maximum size of the dust grains on various outflow parameters, such as the mass ejection rate of the outflow M ̇ , the disk size rdisk, the mass of the central protostar M*, and the internal dust density ρmat. We find the empirical formula for the maximum dust size as a function of the outflow parameters. Parameter a d ,max depends on the parameters as a d ,max ∝ M ̇ 1.0 r disk − 0.44 M * − 0.82 ρ mat − 1.0 . We also find that the dust grains with sizes of 100 μm to 1 mm can be lifted by the outflow and can distribute well outside of the disk when the mass ejection rate of the outflow has a value of 10−7 to 10−6 M⊙ yr−1. This result is consistent with recent observations that show a correlation between the mass ejection rate of the outflow and the spectral index β of the dust opacity at the envelope scale.

DOI： 10.3847/1538-4357/adc806

Fukihara H., Takaishi D., Misugi Y., Sasaki M., Tsukamoto Y. . A statistical approach to interpreting polarized dust emission of filamentary molecular clouds toward an estimate of 3D magnetic field structure . Publications of the Astronomical Society of Japan77 ( 2 ) 277 - 287 2025.4Reviewed

Language：Japanese Publisher：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 RFWHM, 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 RFWHM from the density and magnetic field structure obtained in the 3D-MHD simulations. We find that the mean and variance of RFWHM 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 RFWHM 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

Ohashi S., Muto T., Tsukamoto Y., Kataoka A., Tsukagoshi T., Momose M., Fukagawa M., Sakai N. . Observationally derived magnetic field strength and 3D components in the HD 142527 disk . Nature Astronomy9 ( 4 ) 526 - 534 2025.4Reviewed

Language：Japanese Publisher：Nature Astronomy

The magnetic fields in protoplanetary disks around young stars play an important role in disk evolution and planet formation. Measuring the polarized thermal emission from magnetically aligned grains is a reliable method for tracing magnetic fields. However, it has been difficult to observe magnetic fields from dust polarization in protoplanetary disks because other polarization mechanisms involving grown dust grains become efficient. Here we report multi-wavelength (0.87, 1.3, 2.1 and 2.7 mm) observations of polarized thermal emission in the protoplanetary disk around HD 142527, which shows a lopsided dust distribution. We revealed that smaller dust particles still exhibit magnetic alignment in the southern part of the disk. Furthermore, angular offsets between the observed magnetic field and the disk azimuthal direction were discovered. These offsets can be used to measure the relative strengths of each component of a three-dimensional magnetic field (radial (Br), azimuthal (Bϕ) and vertical (Bz)). Applying this method, we derived the magnetic field around a 200 au radius from the protostar as ∣Br∣:∣Bϕ∣:∣Bz∣ ≈ 0.26:1:0.23 with a strength of ~0.3 mG. Our observations provide some key parameters of magnetic activities, including the plasma beta, which has had to be assumed in theoretical studies. In addition, the radial and vertical angular momentum transfers were found to be comparable, which poses a challenge to theoretical studies of protoplanetary disks.

DOI： 10.1038/s41550-024-02454-x

Wu J., Qiu K., Poidevin F., Bastien P., Liu J., Ching T.C., Bourke T.L., Ward-Thompson D., Pattle K., Johnstone D., Koch P.M., Arzoumanian D., Lee C.W., Fanciullo L., Onaka T., Hwang J., Le Gouellec V.J.M., Soam A., Tamura M., Tahani M., Eswaraiah C., Li H.B., Berry D., Furuya R.S., Coudé S., Kwon W., Lin S.J., Wang J.W., Hasegawa T., Lai S.P., Byun D.Y., Chen Z., Chen H.R.V., Chen W.P., Chen M., Cho J., Choi Y., Choi Y., Choi M., Chrysostomou A., Chung E.J., Dai S., Di Francesco J., Diep P.N., Doi Y., Duan H.Y., Duan Y., Eden D., Fiege J., Fissel L.M., Franzmann E., Friberg P., Friesen R., Fuller G., Gledhill T., Graves S., Greaves J., Griffin M., Gu Q., Han I., Hayashi S., Hoang T., Houde M., Inoue T., Inutsuka S.I., Iwasaki K., Jeong I.G., Könyves V., Kang J.H., Kang M., Karoly J., Kataoka A., Kawabata K., Kim S., Kim M.R., Kim K.H., Kim K.T., Kim J., Kim H., Kim G., Kirchschlager F., Kirk J., Kobayashi M.I.N., Kusune T., Kwon J., Lacaille K., Law C.Y., Lee H., Lee C.F., Lee S.S., Lee J.E., Li D., Li D., Li G., Liu S.Y., Liu T., Liu H.L., Lu X., Lyo A.R., Mairs S. . A Tale of Three: Magnetic Fields along the Orion Integral-shaped Filament as Revealed by the JCMT BISTRO Survey . Astrophysical Journal Letters977 ( 2 ) 2024.12

Language：Japanese Publisher：Astrophysical Journal Letters

As part of the B-fields In Star-forming Region Observations survey, we present James Clerk Maxwell Telescope (JCMT) 850 μm polarimetric observations toward the Orion integral-shaped filament (ISF) that covers three portions known as OMC-1, OMC-2, and OMC-3. The magnetic field threading the ISF seen in the JCMT POL-2 map appears as a tale of three: pinched for OMC-1, twisted for OMC-2, and nearly uniform for OMC-3. A multiscale analysis shows that the magnetic field structure in OMC-3 is very consistent at all the scales, whereas the field structure in OMC-2 shows no correlation across different scales. In OMC-1, the field retains its mean orientation from large to small scales but shows some deviations at small scales. Histograms of relative orientations between the magnetic field and filaments reveal a bimodal distribution for OMC-1, a relatively random distribution for OMC-2, and a distribution with a predominant peak at 90o for OMC-3. Furthermore, the magnetic fields in OMC-1 and OMC-3 both appear to be aligned perpendicular to the fibers, which are denser structures within the filament, but the field in OMC-2 is aligned along with the fibers. All these suggest that gravity, turbulence, and magnetic field are each playing a leading role in OMC-1, 2, and 3, respectively. While OMC-2 and 3 have almost the same gas mass, density, and nonthermal velocity dispersion, there are on average younger and fewer young stellar objects in OMC-3, providing evidence that a stronger magnetic field will induce slower and less efficient star formation in molecular clouds.

DOI： 10.3847/2041-8213/ad93d2

Choi Y., Kwon W., Pattle K., Arzoumanian D., Bourke T.L., Hoang T., Hwang J., Koch P.M., Sadavoy S., Bastien P., Furuya R., Lai S.P., Qiu K., Ward-Thompson D., Berry D., Byun D.Y., Chen H.R.V., Chen W.P., Chen M., Chen Z., Ching T.C., Cho J., Choi M., Choi Y., Coudé S., Chrysostomou A., Chung E.J., Dai S., Debattista V., Di Francesco J., Diep P.N., Doi Y., Duan H.Y., Duan Y., Eswaraiah C., Fanciullo L., Fiege J., Fissel L.M., Franzmann E., Friberg P., Friesen R., Fuller G., Gledhill T., Graves S., Greaves J., Griffin M., Gu Q., Han I., Hasegawa T., Houde M., Hull C.L.H., Inoue T., Inutsuka S.I., Iwasaki K., Jeong I.G., Johnstone D., Karoly J., Könyves V., Kang J.H., Kang M., Kataoka A., Kawabata K., Kemper F., Kim J., Kim S., Kim G., Kim K.H., Kim M.R., Kim K.T., Kim H., Kirchschlager F., Kirk J., Kobayashi M.I.N., Kusune T., Kwon J., Lacaille K., Law C.Y., Lee C.W., Lee H., Lee C.F., Lee J.E., Lee S.S., Li D., Li D., Li G., Li H.B., Lin S.J., Liu H.L., Liu T., Liu S.Y., Liu J., Longmore S., Lu X., Lyo A.R., Mairs S., Matsumura M., Matthews B., Moriarty-Schieven G., Nagata T., Nakamura F. . The JCMT BISTRO Survey: The Magnetic Fields of the IC 348 Star-forming Region . Astrophysical Journal977 ( 1 ) 2024.12

Language：Japanese Publisher：Astrophysical Journal

We present 850 μm polarization observations of the IC 348 star-forming region in the Perseus molecular cloud as part of the B-fields In STar-forming Region Observation survey. We study the magnetic properties of two cores (HH 211 MMS and IC 348 MMS) and a filamentary structure of IC 348. We find that the overall field tends to be more perpendicular than parallel to the filamentary structure of the region. The polarization fraction decreases with intensity, and we estimate the trend by power law and the mean of the Rice distribution fittings. The power indices for the cores are much smaller than 1, indicative of possible grain growth to micron size in the cores. We also measure the magnetic field strengths of the two cores and the filamentary area separately by applying the Davis-Chandrasekhar-Fermi method and its alternative version for compressed medium. The estimated mass-to-flux ratios are 0.45-2.20 and 0.63-2.76 for HH 211 MMS and IC 348 MMS, respectively, while the ratios for the filament are 0.33-1.50. This result may suggest that the transition from subcritical to supercritical conditions occurs at the core scale (∼0.05 pc) in the region. In addition, we study the energy balance of the cores and find that the relative strength of turbulence to the magnetic field tends to be stronger for IC 348 MMS than for HH 211 MMS. The result could potentially explain the different configurations inside the two cores: a single protostellar system in HH 211 MMS and multiple protostars in IC 348 MMS.

DOI： 10.3847/1538-4357/ad88ed

Tsukamoto Y. . Co-evolution of dust grains and protoplanetary disks. II. Structure and evolution of protoplanetary disks: An analytical approach . Publications of the Astronomical Society of Japan76 ( 4 ) 674 - 687 2024.8

Language：Japanese Publisher：Publications of the Astronomical Society of Japan

In our previous study (Tsukamoto et al. 2023b, PASJ, 75, 835), we investigated the formation and early evolution of protoplanetary disks with 3D non-ideal magnetohydrodynamics simulations considering dust growth, and found that the modified equations of the conventional steady accretion disk model that consider magnetic braking, dust growth, and ambipolar diffusion reproduce the disk structure (such as density and vertical magnetic field) obtained from simulations very well. In this paper, as a sequel to our previous study, we analytically investigate the structure and evolution of protoplanetary disks corresponding to Class 0/I young stellar objects using the modified steady accretion disk model combining an analytical model of envelope accretion. We estimate that the disk radius is several astronomical units at the disk formation epoch and increases to several hundred astronomical units at the end of the accretion phase. The disk mass is estimated to be 0.01 ≲ Mdisk ≲ 0.1 M⊙ for a disk with a radius of several tens of astronomical units and a mass accretion rate of Ṁdisk ∼ 10−6 M⊙ yr−1. These estimates seems to be consistent with recent observations. We also found that, with typical disk ionization rates (ζ ≳ 10−19 s−1) and a moderate mass accretion rate (Ṁdisk ≳ 10−8 M⊙ yr−1), magnetorotational instability is suppressed in the disk because of low plasma β and efficient ambipolar diffusion. We argue that the radial profile of specific angular momentum (or rotational velocity) at the disk outer edge should be continuously connected to that of the envelope if the disk evolves by magnetic braking, and should be discontinuous if the disk evolves by an internal angular momentum transport process such as gravitational instability or magnetorotational instability. Future detailed observations of the specific angular momentum profile around the disk outer edge are important for understanding the angular momentum transport mechanism of protoplanetary disks.

DOI： 10.1093/pasj/psae039

Misugi Y., Inutsuka S.I., Arzoumanian D., Tsukamoto Y. . Evolution of the Angular Momentum of Molecular Cloud Cores in Magnetized Molecular Filaments . Astrophysical Journal963 ( 2 ) 2024.3

Language：Japanese Publisher：Astrophysical Journal

The angular momentum of molecular cloud cores plays a key role in the star formation process. However, the evolution of the angular momentum of molecular cloud cores formed in magnetized molecular filaments is still unclear. In this paper, we perform 3D magnetohydrodynamics simulations to reveal the effect of the magnetic field on the evolution of the angular momentum of molecular cloud cores formed through filament fragmentation. As a result, we find that the angular momentum decreases by 30% and 50% at the mass scale of 1 M ⊙ in the case of weak and strong magnetic field, respectively. By analyzing the torques exerted on fluid elements, we identify the magnetic tension as the dominant process for angular momentum transfer for mass scales ≲3 M ⊙ for the strong magnetic field case. This critical mass scale can be understood semianalytically as the timescale of magnetic braking. We show that the anisotropy of the angular momentum transfer due to the presence of a strong magnetic field changes the resultant angular momentum of the core only by a factor of 2. We also find that the distribution of the angle between the rotation axis and the magnetic field does not show strong alignment even just before the first core formation. Our results also indicate that the variety of the angular momentum of the cores is inherited from the difference in the phase of the initial turbulent velocity field. The variety could contribute to the diversity in size and other properties of protoplanetary disks recently reported by observations.

DOI： 10.3847/1538-4357/ad1990

Takaishi D., Tsukamoto Y., Kido M., Takakuwa S., Misugi Y., Kudoh Y., Suto Y. . Formation of Unipolar Outflow and Protostellar Rocket Effect in Magnetized Turbulent Molecular Cloud Cores . Astrophysical Journal963 ( 1 ) 2024.3

Language：Japanese Publisher：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

Tsukamoto Y., Machida M.N., Inutsuka S.I. . Co-evolution of dust grains and protoplanetary disks . Publications of the Astronomical Society of Japan75 ( 5 ) 835 - 852 2023.10

Language：Japanese Publisher：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 α. 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

Kobayashi Y., Takaishi D., Tsukamoto Y. . Cosmic ray ionization rate versus dust fraction: Which plays a crucial role in the early evolution of the circumstellar disc? . Monthly Notices of the Royal Astronomical Society521 ( 2 ) 2661 - 2669 2023.5Reviewed

Language：Japanese Publisher：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

Hwang J., Kim J., Pattle K., Lee C.W., Koch P.M., Johnstone D., Tomisaka K., Whitworth A., Furuya R.S., Kang J.H., Lyo A.R., Chung E.J., Arzoumanian D., Park G., Kwon W., Kim S., Tamura M., Kwon J., Soam A., Han I., Hoang T., Kim K.H., Onaka T., Eswaraiah C., Ward-Thompson D., Liu H.L., Tang X., Chen W.P., Matsumura M., Hoang T.D., Chen Z., Le Gouellec V.J.M., Kirchschlager F., Poidevin F., Bastien P., Qiu K., Hasegawa T., Lai S.P., Byun D.Y., Cho J., Choi M., Choi Y., Choi Y., Jeong I.G., Kang M., Kim H., Kim K.T., Lee J.E., Lee S.S., Lee Y.H., Lee H., Kim M.R., Yoo H., Yun H.S., Chen M., Di Francesco J., Fiege J., Fissel L.M., Franzmann E., Houde M., Lacaille K., Matthews B., Sadavoy S., Moriarty-Schieven G., Tahani M., Ching T.C., Dai Y.S., Duan Y., Gu Q., Law C.Y., Li D., Li D., Li G., Li H.B., Liu T., Lu X., Qian L., Wang H., Wu J., Xie J., Yuan J., Zhang C.P., Zhang G., Zhang Y., Zhou J., Zhu L., Berry D., Friberg P., Graves S., Liu J., Mairs S., Parsons H., Rawlings M., Doi Y., Hayashi S., Hull C.L.H., Inoue T., Inutsuka S.I., Iwasaki K., Kataoka A. . The JCMT BISTRO Survey: A Spiral Magnetic Field in a Hub-filament Structure, Monoceros R2 . Astrophysical Journal941 ( 1 ) 2022.12Reviewed

Language：Japanese Publisher：Astrophysical Journal

We present and analyze observations of polarized dust emission at 850 μm toward the central 1 × 1 pc hub-filament structure of Monoceros R2 (Mon R2). The data are obtained with SCUBA-2/POL-2 on the James Clerk Maxwell Telescope (JCMT) as part of the B-fields in Star-forming Region Observations survey. The orientations of the magnetic field follow the spiral structure of Mon R2, which are well described by an axisymmetric magnetic field model. We estimate the turbulent component of the magnetic field using the angle difference between our observations and the best-fit model of the underlying large-scale mean magnetic field. This estimate is used to calculate the magnetic field strength using the Davis–Chandrasekhar–Fermi method, for which we also obtain the distribution of volume density and velocity dispersion using a column density map derived from Herschel data and the C18O (J = 3 - 2) data taken with HARP on the JCMT, respectively. We make maps of magnetic field strengths and mass-to-flux ratios, finding that magnetic field strengths vary from 0.02 to 3.64 mG with a mean value of 1.0 ± 0.06 mG, and the mean critical mass-to-flux ratio is 0.47 ± 0.02. Additionally, the mean Alfvén Mach number is 0.35 ± 0.01. This suggests that, in Mon R2, the magnetic fields provide resistance against large-scale gravitational collapse, and the magnetic pressure exceeds the turbulent pressure. We also investigate the properties of each filament in Mon R2. Most of the filaments are aligned along the magnetic field direction and are magnetically subcritical.

DOI： 10.3847/1538-4357/ac99e0

Ching T.C., Qiu K., Li D., Ren Z., Lai S.P., Berry D., Pattle K., Furuya R., Ward-Thompson D., Johnstone D., Koch P.M., Lee C.W., Hoang T., Hasegawa T., Kwon W., Bastien P., Eswaraiah C., Wang J.W., Kim K.H., Hwang J., Soam A., Lyo A.R., Liu J., Le Gouellec V.J.M., Arzoumanian D., Whitworth A., Di Francesco J., Poidevin F., Liu T., Coudé S., Tahani M., Liu H.L., Onaka T., Li D., Tamura M., Chen Z., Tang X., Kirchschlager F., Bourke T.L., Byun D.Y., Chen M., Chen H.R.V., Chen W.P., Cho J., Choi Y., Choi Y., Choi M., Chrysostomou A., Chung E.J., Dai Y.S., Diep P.N., Doi Y., Duan Y., Duan H.Y., Eden D., Fanciullo L., Fiege J., Fissel L.M., Franzmann E., Friberg P., Friesen R., Fuller G., Gledhill T., Graves S., Greaves J., Griffin M., Gu Q., Han I., Hayashi S., Houde M., Hull C.L.H., Inoue T., Inutsuka S.I., Iwasaki K., Jeong I.G., Könyves V., Kang J.H., Kang M., Karoly J., Kataoka A., Kawabata K., Kemper F., Kim J., Kim M.R., Kim S., Kim H., Kim K.T., Kim G., Kirk J., Kobayashi M.I.N., Kusune T., Kwon J., Lacaille K., Law C.Y., Lee S.S., Lee H., Lee J.E., Lee C.F., Lee Y.H., Li G. . The JCMT BISTRO-2 Survey: Magnetic Fields of the Massive DR21 Filament . Astrophysical Journal941 ( 2 ) 2022.12Reviewed International coauthorship

Language：Japanese Publisher：Astrophysical Journal

We present 850 μm dust polarization observations of the massive DR21 filament from the B-fields In STar-forming Region Observations (BISTRO) survey, using the POL-2 polarimeter and the SCUBA-2 camera on the James Clerk Maxwell Telescope. We detect ordered magnetic fields perpendicular to the parsec-scale ridge of the DR21 main filament. In the subfilaments, the magnetic fields are mainly parallel to the filamentary structures and smoothly connect to the magnetic fields of the main filament. We compare the POL-2 and Planck dust polarization observations to study the magnetic field structures of the DR21 filament on 0.1-10 pc scales. The magnetic fields revealed in the Planck data are well-aligned with those of the POL-2 data, indicating a smooth variation of magnetic fields from large to small scales. The plane-of-sky magnetic field strengths derived from angular dispersion functions of dust polarization are 0.6-1.0 mG in the DR21 filament and ∼0.1 mG in the surrounding ambient gas. The mass-to-flux ratios are found to be magnetically supercritical in the filament and slightly subcritical to nearly critical in the ambient gas. The alignment between column density structures and magnetic fields changes from random alignment in the low-density ambient gas probed by Planck to mostly perpendicular in the high-density main filament probed by James Clerk Maxwell Telescope. The magnetic field structures of the DR21 filament are in agreement with MHD simulations of a strongly magnetized medium, suggesting that magnetic fields play an important role in shaping the DR21 main filament and subfilaments.

DOI： 10.3847/1538-4357/ac9dfb

Tsukamoto Y., Okuzumi S. . Impact of Dust Size Distribution Including Large Dust Grains on Magnetic Resistivity: An Analytical Approach . Astrophysical Journal934 ( 1 ) 2022.7Reviewed

Authorship：Lead author Language：Japanese Publisher：Astrophysical Journal

This paper investigates the impact of dust size distribution on magnetic resistivity. In particular, we focus on its impact when the maximum dust size significantly increases from a submicron level. The first half of the paper describes our calculation method for magnetic resistivity based on the model of Draine & Sutin and shows that the method reproduces the results of more realistic chemical reaction network calculations reasonably well. Then, we describe the results of the resistivity calculations for dust distributions with large maximum dust grains. Our results show that resistivity tends to decrease with dust growth, which is particularly true when the dust size power exponent q is q = 2.5. On the other hand, the decrease is less pronounced when the dust size power exponent q is q = 3.5, i.e., when the small dust is also responsible for the dust cross section. Our results suggest that detailed dust coagulation and fragmentation processes play a vital role in the magnetic resistivities in protostar formation.

DOI： 10.3847/1538-4357/ac7b7b

Tsukamoto Y. . Formation and early evolution of protoplanetary disk determined by the interaction between magnetic field and weakly ionized plasma . Planetary People - The Japanese Society for Planetary Sciences31 ( 1 ) 6 - 17 2022.3Invited Reviewed

Kwon W., Pattle K., Sadavoy S., Hull C.L.H., Johnstone D., Ward-Thompson D., Francesco J.D., Koch P.M., Furuya R., Doi Y., Le Gouellec V.J.M., Hwang J., Lyo A.R., Soam A., Tang X., Hoang T., Kirchschlager F., Eswaraiah C., Fanciullo L., Kim K.H., Onaka T., Könyves V., Kang J.H., Lee C.W., Tamura M., Bastien P., Hasegawa T., Lai S.P., Qiu K., Berry D., Arzoumanian D., Bourke T.L., Byun D.Y., Chen W.P., Chen H.R.V., Chen M., Chen Z., Ching T.C., Cho J., Choi Y., Choi M., Chrysostomou A., Chung E.J., Coudé S., Dai S., Diep P.N., Duan Y., Duan H.Y., Eden D., Fiege J., Fissel L.M., Franzmann E., Friberg P., Friesen R., Fuller G., Gledhill T., Graves S., Greaves J., Griffin M., Gu Q., Han I., Hatchell J., Hayashi S., Houde M., Inoue T., Inutsuka S.I., Iwasaki K., Jeong I.G., Kang M., Karoly J., Kataoka A., Kawabata K., Kemper F., Kim K.T., Kim G., Kim M.R., Kim S., Kim J., Kirk J., Kobayashi M.I.N., Kusune T., Kwon J., Lacaille K., Law C.Y., Lee C.F., Lee Y.H., Lee H., Lee J.E., Lee S.S., Li D., Li D., Li H.B., Lin S.J., Liu S.Y., Liu H.L., Liu J., Liu T., Lu X., Mairs S., Matsumura M. . B-fields in Star-forming Region Observations (BISTRO): Magnetic Fields in the Filamentary Structures of Serpens Main . Astrophysical Journal926 ( 2 ) 2022.2Reviewed International coauthorship

Language：Japanese Publisher：Astrophysical Journal

We present 850 μm polarimetric observations toward the Serpens Main molecular cloud obtained using the POL-2 polarimeter on the James Clerk Maxwell Telescope as part of the B-fields In STar-forming Region Observations survey. These observations probe the magnetic field morphology of the Serpens Main molecular cloud on about 6000 au scales, which consists of cores and six filaments with different physical properties such as density and star formation activity. Using the histogram of relative orientation (HRO) technique, we find that magnetic fields are parallel to filaments in less-dense filamentary structures where NH2<0.93×1022 cm-2 (magnetic fields perpendicular to density gradients), while they are perpendicular to filaments (magnetic fields parallel to density gradients) in dense filamentary structures with star formation activity. Moreover, applying the HRO technique to denser core regions, we find that magnetic field orientations change to become perpendicular to density gradients again at NH2≈4.6×1022 cm-2. This can be interpreted as a signature of core formation. At NH2≈16×1022 cm-2, magnetic fields change back to being parallel to density gradients once again, which can be understood to be due to magnetic fields being dragged in by infalling material. In addition, we estimate the magnetic field strengths of the filaments (B POS = 60-300 μG)) using the Davis-Chandrasekhar-Fermi method and discuss whether the filaments are gravitationally unstable based on magnetic field and turbulence energy densities.

DOI： 10.3847/1538-4357/ac4bbe

Tsukamoto Y. . "ashfall" Induced by Molecular Outflow in Protostar Evolution . Astrophysical Journal Letters920 ( 2 ) 2021.10Reviewed

Authorship：Lead author Language：Japanese Publisher：Astrophysical Journal Letters

Dust growth and its associated dynamics play key roles in the first phase of planet formation in young stellar objects. Observations have detected signs of dust growth in very young protoplanetary disks. Furthermore, signs of planet formation, gaps in the disk at a distance of several tens of au from the central protostar, are also reported. From a theoretical point of view, however, planet formation in the outer regions is difficult due to the rapid inward drift of dust, called the radial drift barrier. Here, on the basis of three-dimensional magnetohydrodynamical simulations of disk evolution with dust growth, we propose a mechanism called the "ashfall"phenomenon, induced by a powerful molecular outflow driven by a magnetic field that may circumvent the radial drift barrier. We find that the large dust that grows to a size of about a centimeter in the inner region of a disk is entrained by an outflow from the disk. Then, large dust decoupled from gas is ejected from the outflow due to centrifugal force, enriching the grown dust in the envelope and eventually falls onto the outer edge of the disk. The overall process is similar to the behavior of ashfall from volcanic eruptions. In the ashfall phenomenon, the Stokes number of dust increases by reaccreting to the less dense disk outer edge. This may allow the dust grains to overcome the radial drift barrier. Consequently, the ashfall phenomenon can provide a crucial assist for making the formation of the planetesimals in outer regions of the disk possible, and hence the formation of wide-orbit planets and gaps.

DOI： 10.3847/2041-8213/ac2b2f

Takaishi D. . A new formation scenario of a counter-rotating circumstellar disk: Spiral-arm accretion from a circumbinary disk in a triple protostar system . Publications of the Astronomical Society of Japan73 ( 5 ) L25 - L30 2021.10Reviewed

Language：Japanese Publisher：Publications of the Astronomical Society of Japan

We present the evolution of rotational directions of circumstellar disks in a triple protostar system simulated from a turbulent molecular cloud core with no magnetic field. We find a new formation pathway of a counter-rotating circumstellar disk in such triple systems. The tertiary protostar forms via the circumbinary disk fragmentation and the initial rotational directions of all three circumstellar disks are almost parallel to that of the orbital motion of the binary system. Their mutual gravito-hydrodynamical interaction for the subsequent ∼104 yr greatly disturbs the orbit of the tertiary, and the rotational directions of the tertiary disk and star are reversed due to the spiral-arm accretion of the circumbinary disk. The counter-rotation of the tertiary circumstellar disk continues to the end of the simulation (∼6.4 × 104 yr after its formation), implying that the counter-rotating disk is long-lived. This new formation pathway during the disk evolution in Class 0/I young stellar objects possibly explains the counter-rotating disks recently discovered by ALMA.

DOI： 10.1093/pasj/psab084

Ichikawa T. . Misaligned circumstellar disks and orbital motion of the young binary xz tau . Astrophysical Journal919 ( 1 ) 2021.9Reviewed

Language：Japanese Publisher：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

Lyo A.R. . The JCMT BISTRO survey: An 850/450μm polarization study of NGC 2071IR in Orion B . Astrophysical Journal918 ( 2 ) 2021.9Reviewed

Language：Japanese Publisher：Astrophysical Journal

We present the results of simultaneous 450 μm and 850 μm polarization observations toward the massive star-forming region NGC 2071IR, a target of the BISTRO (B-fields in STar-forming Region Observations) Survey, using the POL-2 polarimeter and SCUBA-2 camera mounted on the James Clerk Maxwell Telescope. We find a pinched magnetic field morphology in the central dense core region, which could be due to a rotating toroidal disklike structure and a bipolar outflow originating from the central young stellar object IRS 3. Using the modified Davis–Chandrasekhar–Fermi method, we obtain a plane-of-sky magnetic field strength of 563 ± 421 μG in the central ∼0.12 pc region from 850 μm polarization data. The corresponding magnetic energy density of 2.04 × 10-8 erg cm-3 is comparable to the turbulent and gravitational energy densities in the region. We find that the magnetic field direction is very well aligned with the whole of the IRS 3 bipolar outflow structure. We find that the median value of polarization fractions is 3.0% at 450 μm in the central 3′ region, which is larger than the median value of 1.2% at 850 μm. The trend could be due to the better alignment of warmer dust in the strong radiation environment. We also find that polarization fractions decrease with intensity at both wavelengths, with slopes, determined by fitting a Rician noise model of 0.59 ± 0.03 at 450 μm and 0.36 ± 0.04 at 850 μm, respectively. We think that the shallow slope at 850 μm is due to grain alignment at the center being assisted by strong radiation from the central young stellar objects.

DOI： 10.3847/1538-4357/ac0ce9

Tsukamoto Y. . Conditions for Justifying Single-fluid Approximation for Charged and Neutral Dust Fluids and a Smoothed Particle Magnetohydrodynamics Method for Dust-Gas Mixture . Astrophysical Journal913 ( 2 ) 2021.6Reviewed

Authorship：Lead author Language：Japanese Publisher：Astrophysical Journal

We describe a numerical scheme for magnetohydrodynamics simulations of dust-gas mixture by extending smoothed particle magnetohydrodynamics. We employ the single-species particle approach to describe dust-gas mixture with several modifications from the previous studies. We assume that the charged and neutral dust can be treated as single-fluid, that the electromagnetic force acts on the gas, and that that acting on the charged dust is negligible. The validity of these assumptions in the context of protostar formation is not obvious and is extensively evaluated. By investigating the electromagnetic force and electric current with terminal velocity approximation, it is found that as the dust size increases, the contribution of dust to them becomes smaller and negligible. We conclude that our assumption that the electromagnetic force on the dusts is negligible is valid for the dust size with a d ⪆ 10 μm. On the other hand, they do not produce the numerical artifact for the dust a d ≲ 10 μm in the envelope and disk, where the perfect coupling between gas and dust is realized. However, we also found that our assumptions may break down in outflow (or under an environment with very strong magnetic field and low density) for the dust a d ≲ 10 μm. We conclude that our assumptions are valid in almost all cases where macroscopic dust dynamics is important in the context of protostar formation. We conduct numerical tests of dusty waves, dusty magnetohydrodynamics shocks, and gravitational collapse of magnetized cloud cores with our simulation code. The results show that our numerical scheme well reproduces the dust dynamics in the magnetized medium.

DOI： 10.3847/1538-4357/abf5db

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