Convection Enhances Magnetic Turbulence in AM CVn Accretion Disks
| Autor: | Peter H. Hauschildt, Matthew S. B. Coleman, Shigenobu Hirose, Omer Blaes |
|---|---|
| Rok vydání: | 2018 |
| Předmět: |
Physics
Convection Opacity 010308 nuclear & particles physics White dwarf FOS: Physical sciences Astronomy and Astrophysics Astrophysics Effective temperature 01 natural sciences Accretion (astrophysics) Astrophysics - Solar and Stellar Astrophysics Space and Planetary Science Magnetorotational instability 0103 physical sciences Thermal Astrophysics::Solar and Stellar Astrophysics Magnetohydrodynamics 010303 astronomy & astrophysics Astrophysics::Galaxy Astrophysics Solar and Stellar Astrophysics (astro-ph.SR) |
| DOI: | 10.48550/arxiv.1803.04381 |
| Popis: | We present the results of local, vertically stratified, radiation magnetohydrodynamic shearing box simulations of magnetorotational instability (MRI) turbulence for a (hydrogen poor) composition applicable to accretion disks in AM CVn type systems. Many of these accreting white dwarf systems are helium analogues of dwarf novae (DNe). We utilize frequency-integrated opacity and equation of state tables appropriate for this regime to accurately portray the relevant thermodynamics. We find bistability of thermal equilibria in the effective temperature, surface mass density plane typically associated with disk instabilities. Along this equilibrium curve (i.e. the S-curve) we find that the stress to thermal pressure ratio $\alpha$ varied with peak values of $\sim 0.15$ near the tip of the upper branch. Similar to DNe, we found enhancement of $\alpha$ near the tip of the upper branch caused by convection; this increase in $\alpha$ occurred despite our choice of zero net vertical magnetic flux. Two notable differences we find between DN and AM CVn accretion disk simulations are that AM CVn disks are capable of exhibiting persistent convection in outburst, and ideal MHD is valid throughout quiescence for AM CVns. In contrast, DNe simulations only show intermittent convection, and non-ideal MHD effects are likely important in quiescence. By combining our previous work with these new results, we also find that convective enhancement of the MRI is anticorrelated with mean molecular weight. Comment: 15 pages, 10 figures, accepted for publication in ApJ |
| Databáze: | OpenAIRE |
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