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Title: Global MHD Simulations of Accretion Disks in Cataclysmic Variables (CVs). II. The Relative Importance of MRI and Spiral Shocks

Abstract

We perform global three-dimensional MHD simulations of unstratified accretion disks in cataclysmic variables (CVs). By including mass inflow via an accretion stream, we are able to evolve the disk to a steady state. We investigate the relative importance of spiral shocks and the magnetorotational instability (MRI) in driving angular momentum transport and how each depend on the geometry and strength of the seed magnetic field and the Mach number of the disk (where Mach number is the ratio of the azimuthal velocity and the sound speed of gas). We use a locally isothermal equation of state and adopt temperature profiles that are consistent with CV disk observations. Our results indicate that the relative importance of spiral shocks and MRI in driving angular momentum transport is controlled by the gas Mach number and the seed magnetic field strength. MRI and spiral shocks provide comparable efficiency of angular momentum transport when the disk Mach number is around 10 and the seed magnetic field has plasma β=400 (where β is the ratio of gas pressure and magnetic pressure). The MRI dominates whenever the seed field strength, or the disk Mach number, is increased. Among all of our simulations, the effective viscosity parameter α{sub eff}∼0.016--0.1 after MRImore » saturates and the disk reaches steady state. Larger values of α{sub eff} are favored when the seed magnetic field has vertical components or the flow has stronger magnetization (1/β). Our models all indicate that the role of MRI in driving angular momentum transport thus mass accretion in CV disks is indispensable, especially in cool disks with weak spiral shocks.« less

Authors:
;  [1];  [2]
  1. Dept. of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States)
  2. Department of Physics and Astronomy, University of Nevada, Las Vegas, 4505 South Maryland Parkway, Las Vegas, NV 89154 (United States)
Publication Date:
OSTI Identifier:
22872703
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 841; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCRETION DISKS; ANGULAR MOMENTUM; COMPARATIVE EVALUATIONS; COMPUTERIZED SIMULATION; EFFICIENCY; EQUATIONS OF STATE; MACH NUMBER; MAGNETIC FIELDS; MAGNETIZATION; MAGNETOHYDRODYNAMICS; MASS; NMR IMAGING; NOVAE; PLASMA; SEEDS; SOUND WAVES; THREE-DIMENSIONAL CALCULATIONS; VISCOSITY

Citation Formats

Ju, Wenhua, Stone, James M., and Zhu, Zhaohuan. Global MHD Simulations of Accretion Disks in Cataclysmic Variables (CVs). II. The Relative Importance of MRI and Spiral Shocks. United States: N. p., 2017. Web. doi:10.3847/1538-4357/AA705D.
Ju, Wenhua, Stone, James M., & Zhu, Zhaohuan. Global MHD Simulations of Accretion Disks in Cataclysmic Variables (CVs). II. The Relative Importance of MRI and Spiral Shocks. United States. https://doi.org/10.3847/1538-4357/AA705D
Ju, Wenhua, Stone, James M., and Zhu, Zhaohuan. 2017. "Global MHD Simulations of Accretion Disks in Cataclysmic Variables (CVs). II. The Relative Importance of MRI and Spiral Shocks". United States. https://doi.org/10.3847/1538-4357/AA705D.
@article{osti_22872703,
title = {Global MHD Simulations of Accretion Disks in Cataclysmic Variables (CVs). II. The Relative Importance of MRI and Spiral Shocks},
author = {Ju, Wenhua and Stone, James M. and Zhu, Zhaohuan},
abstractNote = {We perform global three-dimensional MHD simulations of unstratified accretion disks in cataclysmic variables (CVs). By including mass inflow via an accretion stream, we are able to evolve the disk to a steady state. We investigate the relative importance of spiral shocks and the magnetorotational instability (MRI) in driving angular momentum transport and how each depend on the geometry and strength of the seed magnetic field and the Mach number of the disk (where Mach number is the ratio of the azimuthal velocity and the sound speed of gas). We use a locally isothermal equation of state and adopt temperature profiles that are consistent with CV disk observations. Our results indicate that the relative importance of spiral shocks and MRI in driving angular momentum transport is controlled by the gas Mach number and the seed magnetic field strength. MRI and spiral shocks provide comparable efficiency of angular momentum transport when the disk Mach number is around 10 and the seed magnetic field has plasma β=400 (where β is the ratio of gas pressure and magnetic pressure). The MRI dominates whenever the seed field strength, or the disk Mach number, is increased. Among all of our simulations, the effective viscosity parameter α{sub eff}∼0.016--0.1 after MRI saturates and the disk reaches steady state. Larger values of α{sub eff} are favored when the seed magnetic field has vertical components or the flow has stronger magnetization (1/β). Our models all indicate that the role of MRI in driving angular momentum transport thus mass accretion in CV disks is indispensable, especially in cool disks with weak spiral shocks.},
doi = {10.3847/1538-4357/AA705D},
url = {https://www.osti.gov/biblio/22872703}, journal = {Astrophysical Journal},
issn = {0004-637X},
number = 1,
volume = 841,
place = {United States},
year = {2017},
month = {5}
}