A subgiant donor of mass fills its Roche lobe and transfers mass because its envelope…

PHYSICS · Subjective · Fermi University Physics · Astrophysics & Cosmology · Stellar death and compact objects · Stellar death and compact objects

Stars from the Inside, Ch Accretion power: mass transfer, discs and the weighing of black holes

Problem

A subgiant donor of mass

M_1 = 1.5\,M_\odot

fills its Roche lobe and transfers mass because its envelope expands as it crosses toward the giant branch, on a timescale

t_{\rm exp} = 5\times10^{7}\,\mathrm{yr}

. Estimate the mass-transfer rate driven by this expansion, using the order-of-magnitude estimate

\dot M \sim M_1/t_{\rm exp}

. Give the answer in both

M_\odot\,\mathrm{yr^{-1}}

and

\mathrm{kg\,s^{-1}}