A new treatment of mass transfer in stellar population algorithms

In binary systems, mass transfer between stars obscures their earlier history. The changes in surface properties are complex and often crudely simplified in stellar population codes.
In this talk, I present a new approach to derive an improved prescription for mass transfer episodes, developed for the binary_c stellar population algorithm. Relying on a dedicated grid of MESA models, I compute the response of the stellar surface to an accretion pulse (that is the injection of mass over a very short time). This yields a map of the mass-radius exponents, that quantify the stability of the transfer, over the whole parameter space.
I will then discuss future developments, to describe episodic accretion as a series of impulses and quantify the occurrence of common-envelope phases or include periastron mass transfer in eccentric systems more accurately.