WIND-ACCRETION DISKS IN WIDE BINARIES, SECOND-GENERATION PROTOPLANETARY DISKS, AND ACCRETION ONTO WHITE DWARFS

Abstract

Mass transfer from an evolved donor star to its binary companion is a standard feature of stellar evolution in binaries. In wide binaries, the companion star captures some of the mass ejected in a wind by the primary star. The captured material forms an accretion disk. Here, we study the evolution of wind-accretion disks, using a numerical approach which allows us to follow the long term evolution. For a broad range of initial conditions, we derive the radial density and temperature profiles of the disk. In most cases, wind-accretion leads to long-lived stable disks over the lifetime of the AGB donor star. The disks have masses of a few times 10^{-5}-10^{-3} M_sun, with surface density and temperature profiles that follow broken power-laws. The total mass in the disk scales approximately linearly with the viscosity parameter used. Roughly 50% to 80% of the mass falling into the disk accretes onto the central star; the rest flows out through the outer edge of the disk into the stellar wind of the primary. For systems with large accretion rates, the secondary accretes as much as 0.1 M_sun. When the secondary is a white dwarf, accretion naturally leads to nova and supernova eruptions. For all types of secondary star, the surface density and temperature profiles of massive disks resemble structures observed in protoplanetary disks, suggesting that coordinated observational programs might improve our understanding of uncertain disk physics.