arXiv subjects

Kazuhiro Kanagawa

Publications and source records attributed to Kazuhiro Kanagawa.

21 records · Page 2Linked to original sources

arXiv2023

Multiple Rings and Asymmetric Structures in the Disk of SR 21

Crescent-like asymmetric dust structures discovered in protoplanetary disks indicate dust aggregations. Thus, the research on them helps us understand the planet formation process. Here we analyze the ALMA data of the protoplanetary disk around the T-Tauri star SR 21, which has asymmetric structures detected in previous sub-millimeter observations. Imaged at ALMA Band 6 (1.3 mm) with a spatial resolution of about 0.$\arcsec$04, the disk is found to consist of two rings and three asymmetric structures, with two of the asymmetric structures being in the same ring. Compared to the Band 6 image, the Band 3 (2.7 mm) image also shows the three asymmetric structures but with some clumps. The elongated asymmetric structures in the outer ring could be due to the interactions of a growing planet. By fitting the Band 3 and Band 6 dust continuum data, two branches of solutions of maximum dust size in the disk are suggested: one is larger than 1 mm, and the other is smaller than 300 $μm$. High-resolution continuum observations at longer wavelengths as well as polarization observations can help break the degeneracy. We also suggest that the prominent spiral previously identified in VLT/SPHERE observations to the south of the star at 0.$\arcsec$25 may be the scattered light counterpart of the Inner Arc, and the structure is a dust-trapping vortex in nature. The discovered features in SR 21 make it a good target for studying the evolution of asymmetric structures and planet formation.

astro-ph.EP↗

arXiv2019

The detection of dust gap-ring structure in the outer region of the CR Cha protoplanetary disk

We observe the dust continuum at 225 GHz and CO isotopologue (12CO, 13CO, and C18O) J=2-1 emission lines toward the CR Cha protoplanetary disk using the Atacama Large Millimeter/Submillimeter Array (ALMA). The dust continuum image shows a dust gap-ring structure in the outer region of the dust disk. A faint dust ring is also detected around 120 au beyond the dust gap. The CO isotopologue lines indicate that the gas disk is more extended than the dust disk. The peak brightness temperature of the 13CO line shows a small bump around 130 au while 12CO and C18O lines do not show. We investigate two possible mechanisms for reproducing the observed dust gap-ring structure and a gas temperature bump. First, the observed gap structure can be opened by a Jupiter mass planet using the relation between the planet mass and the gap depth and width. Meanwhile, the radiative transfer calculations based on the observed dust surface density profile show that the observed dust ring could be formed by dust accumulation at the gas temperature bump, that is, the gas pressure bump produced beyond the outer edge of the dust disk.

astro-ph.EP↗

arXiv2018

Slowing Down Type II Migration of Gas Giants to Match Observational Data

The mass and semimajor axis distribution of gas giants in exoplanetary systems obtained by radial velocity surveys shows that super-jupiter-mass planets are piled up at > 1 au, while jupiter/sub-jupiter-mass planets are broadly distributed from ~0.03 au to beyond 1 au. This feature has not been explained by theoretical predictions. In order to reconcile this inconsistency, we investigate evolution of gas giants with a new type II migration formula by Kanagawa et al. (2018), by comparing the migration, growth timescales of gas giants, and disk lifetime and by population synthesis simulation. While the classical migration model assumes that a gas giant opens up a clear gap in the protoplanetary disk and the planet migration tied to the disk gas accretion, recent high-resolution simulations show that the migration of gap-opening planets is decoupled from the disk gas accretion and Kanagawa et al. (2018) proposed that type II migration speed is no other than type I migration speed with the reduced disk gas surface density in the gap. We show that with this new formula, type II migration is significantly reduced for super-jupiter-mass planets, if the disk accretion is driven by the disk wind as suggested by recent MHD simulations. Population synthesis simulations show that super-jupiter-mass planets remain at > 1 au without any additional ingredient such as disk photoevaporation. Therefore, the mystery of the pile-up of gas giants at > 1 au would be theoretically solved, if the new formula is confirmed and wind-driven disk accretion dominates.

astro-ph.EP↗