Takanori Ichikawa | Searcharxiv

arXiv2021

Misaligned Circumstellar Disks and Orbital Motion of the Young Binary XZ Tau

We report our analyses of the multi-epoch (2015-2017) 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 deg for XZ Tau A and ~ 130 deg 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+0.025-0.034, a = 0''.172+0''.002-0''.003, and ω = -54.2+2.0-4.7 deg) 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.

astro-ph.SR↗

arXiv2020

The First VERA Astrometry Catalog

We present the first astrometry catalog from the Japanese VLBI (very long baseline interferometer) project VERA (VLBI Exploration of Radio Astrometry). We have compiled all the astrometry results from VERA, providing accurate trigonometric annual parallax and proper motion measurements. In total, 99 maser sources are listed in the VERA catalog. Among them, 21 maser sources are newly reported while the rest of 78 sources are referred to previously published results or those in preparation for forthcoming papers. The accuracy in the VERA astrometry are revisited and compared with those from the other VLBI astrometry projects such as BeSSeL (The Bar and Spiral Structure Legacy) Survey and GOBELINS (the Gould's Belt Distances Survey) with the VLBA (Very Long Baseline Array). We have confirmed that most of the astrometry results are consistent with each other, and the largest error sources are due to source structure of the maser features and their rapid variation, along with the systematic calibration errors and different analysis methods. Combined with the BeSSeL results, we estimate the up-to-date fundamental Galactic parameter of $R_{0}=7.92\pm0.16_{\rm{stat.}}\pm0.3_{\rm{sys.}}$~kpc and $Ω_{\odot}=30.17\pm0.27_{\rm{stat.}}\pm0.3_{\rm{sys.}}$~km~s$^{-1}$~kpc$^{-1}$, where $R_{0}$ and $Ω_{\odot}$ are the distance from the Sun to the Galactic center and the Sun's angular velocity of the Galactic circular rotation, respectively.

astro-ph.GA↗