Hydrodynamical models of the $\beta$ Lyr A circumstellar disc

Abstract

We study dynamics of circumstellar discs, with a focus on the $\beta$ Lyrae A binary system. This system with ongoing mass transfer has been extensively observed, using photometry, spectroscopy and interferometry. All these observations were recently interpreted using a radiation-transfer kinematic model. We modified the analytical Shakura-Sunyaev models for a general opacity prescription, and derived radial profiles of various quantities. These profiles were computed for the fixed accretion rate, $\dot{M}=2\times 10^{-5}{M}_{\odot }{\mathrm{yr}}^{-1}$, inferred from the observed rate of change of the binary period. More general models were computed numerically, using 1-dimensional radiative hydrodynamics, accounting for viscous, radiative as well as irradiation terms. The initial conditions were taken from the analytical models. To achieve the accretion rate, the surface density~$\Sigma$ must be much higher (of the order of $10^4\mathrm{kg}{\mathrm{m}}^{-2}$ for the viscosity parameter $\alpha =0.1$) than in the kinematic model. Viscous dissipation and radiative cooling in the optically thick regime lead to a high midplane temperature~$T$ (up to $10^5\mathrm{K}$). The accretion disc is still gas pressure dominated with the opacity close to Kramers one. To reconcile temperature profiles with observations, we had to distinguish three different temperatures: midplane, atmospheric and irradiation. The latter two are comparable to observations (30000 to 12000 $K$). We demonstrate that the aspect ratio~$H$ of 0.08 can be achieved in a hydrostatic equilibrium, as opposed to previous works considering the disc to be vertically unstable.

17 pages, 26 figures, Accepted to Astronomy & Astrophysics

References in corpus (9)

• Accretion disc viscosity: how big is alpha?
• First Resolved Images of the Eclipsing and Interacting Binary Beta Lyrae
• Eccentricity excitation and merging of planetary embryos heated by pebble accretion
• The B-type Binaries Characterisation Programme II. VFTS 291: A stripped star from a recent mass transfer phase
• Birth of a Be star: an APOGEE search for Be stars forming through binary mass transfer
• Radiative scale-height and shadows in protoplanetary disks
• Model for the long and orbital brightness variability of the $\beta$ Lyrae type binary OGLE-BLG-ECL-157529
• V4142 Sgr: a Double Periodic Variable with an accretor surrounded by the accretion-disk's atmosphere
• New Galactic $\beta$ Lyrae-type Binaries Showing Superorbital Photometric Cycles