Convection in axially symmetric accretion discs with microscopic transport coefficients
Abstract
The vertical structure of stationary thin accretion discs is calculated from the energy balance equation with heat generation due to microscopic ion viscosity η and electron heat conductivity κ, both depending on temperature. In the optically thin discs it is found that for the heat conductivity increasing with temperature, the vertical temperature gradient exceeds the adiabatic value at some height, suggesting convective instability in the upper disc layer. There is a critical Prandtl number, Pr = 4/9, above which a Keplerian disc become fully convective. The vertical density distribution of optically thin laminar accretion discs as found from the hydrostatic equilibrium equation cannot be generally described by a polytrope but in the case of constant viscosity and heat conductivity. In the optically thick discs with radiation heat transfer, the vertical disc structure is found to be convectively stable for both absorptiondominated and scatteringdominated opacities, unless a very steep dependence of the viscosity coefficient on temperature is assumed. A polytropiclike structure in this case is found for Thomson scatteringdominated opacity.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 January 2017
 DOI:
 10.1093/mnras/stw2348
 arXiv:
 arXiv:1609.03799
 Bibcode:
 2017MNRAS.464..410M
 Keywords:

 accretion;
 accretion discs;
 convection;
 Astrophysics  High Energy Astrophysical Phenomena;
 Physics  Fluid Dynamics
 EPrint:
 8 pages, 3 figures, published in MNRAS