Formation of massive close binaries I. Detached evolution

Understand

We explore the initial conditions that lead to detached binary evolution of massive pre-MS binaries and ask how large a fraction of the observed binary systems may have been initially formed as low-mass protobinaries and later undergone a significant accretion phase while remaining detached.

• We develop a family of analytic models to describe the orbital separation, $a$, and mass ratio, $q$, evolution.
• For a given mass accretion rate onto the binary system, we define a recipe for distributing this mass between the two components.
• For this we introduce a parameter $\eta$, such that $\frac{\dot{M}_2}{\dot{M}_1}=q^\eta$ at any time, to determine the binary mass ratio evolution.