Modelling the Break in the Specific Angular Momentum within the Envelope-Disk Transition Zone
Academia Sinica Institute of Astronomy and Astrophysics（中央研究院天文及天文物理研究所）；Canadian Institute for Theoretical Astrophysics, University of Toronto（多伦多大学加拿大理论天体物理研究所）；The University of Western Ontario, Department of Physics and Astronomy（韦仕敦大学（西安大略大学）物理与天文系）；Institut für Astro- und Teilchenphysik, Universität Innsbruck（因斯布鲁克大学天文与粒子物理研究所）；Department of Astrophysics, University of Vienna（维也纳大学天体物理系）；Research Institute of Physics, Southern Federal University（南联邦大学物理研究所）；Korea Astronomy and Space Science Institute（韩国天文与空间科学研究所）；Division of Astronomy and Space Science, University of Science and Technology（韩国科学技术院天文与空间科学学部）
Indrani Das, Shantanu Basu, Nagayoshi Ohashi, Eduard Vorobyov, Yusuke Aso
The observations of protostellar systems show a transition in the radial profile of specific angular momentum (and rotational velocity), evolving from $j\sim{\rm constant}$ ($v_ϕ\sim r^{-1}$) in the infalling-rotating envelope to $j\propto r^{1/2}$ ($v_ϕ\sim r^{-1/2}$) in the Keplerian disk. We employ global MHD disk simulations of gravitational collapse starting from a supercritical prestellar core, that forms a disk and envelope structure in a self-consistent manner, in order to determine the physics of the Envelope-Disk Transition Zone (ENDTRANZ). Our numerical results show the transition from the infalling-rotating envelope to Keplerian disk happens through a jump in the $j-r$ profile over a finite radial range, which is characterized by the positive local gravitational torques. The outer edge of the ENDTRANZ is identified where the radial infall speed ($v_r$) begins a sharp decline in magnitude and $j$ begins a transition from $j\sim{\rm constant}$ toward $j\sim r^{1/2}$. Moving radially inward, the centrifugal radius ($r_{\rm CR}$) is defined where $v_ϕ$ first transitions to Keplerian velocity at the disk's edge. Farther inward of $r_{\rm CR}$, model disk develops a super-Keplerian rotation due to self-gravity. The inner edge of the ENDTRANZ is defined at the centrifugal barrier ($r_{\rm CB}$) where $v_r$ drops to negligible values. Inside $r_{\rm CB}$, a net negative gravitational torque drives mass accretion onto the protostar. On observational grounds, we identify a jump in the observed $j-r$ profile in L1527 IRS for the first time using the ALMA eDisk data. Comparison with the numerical radial behavior from our MHD disk simulations suggests the observed $j-r$ jump can be used as a kinematical tracer for the existence of ENDTRANZ. Our results offer insights into the observable imprint of angular momentum redistribution mechanisms during star-disk formation.
Atmospheric Signatures of Common Envelope Evolution in White Dwarf Planets
Massachusetts Institute of Technology（麻省理工学院）；University of Texas at Austin（德克萨斯大学奥斯汀分校）；University of Wisconsin-Madison（威斯康星大学麦迪逊分校）；University of California, Santa Cruz（加州大学圣克鲁兹分校）
Nonlinear internal waves breaking in stellar radiation zones. Parametrisation for the transport of angular momentum: bridging geophysical to stellar fluid dynamics
