Binary Evolution: Roche Lobe Overflow and Blue Stragglers

TL;DR

This paper reviews the theoretical mechanisms of mass transfer via Roche lobe overflow in binary systems, explaining how it leads to blue straggler formation and comparing predictions with observations.

Contribution

It provides a comprehensive overview of the classification, response types, and stability criteria of Roche lobe overflow, and discusses its role in blue straggler formation.

Findings

Theoretical responses depend on envelope type and timescale.

Stability of mass transfer influences blue straggler formation.

Comparison with observed systems supports the theory.

Abstract

One of the principal mechanisms that is responsible for the origin of blue stragglers is mass transfer that takes place while one of the binary companions overfills its Roche lobe. In this Chapter, we overview the theoretical understanding of mass transfer via Roche lobe overflow: classification, how both the donor and of the accretor respond to the mass transfer on different timescales (adiabatic response, equilibrium response, superadiabatic response, time-dependent response) for different types of their envelopes (convective and radiative). These responses, as well as the assumption on how liberal the process is, are discussed in terms of the stability of the ensuing mass transfer. The predictions of the theory of mass transfer via Roche lobe overflow are then briefly compared with the observed mass-transferring systems with both degenerate and non-degenerate donors. We conclude with the discussion which cases of mass transfer and which primordial binaries could be responsible for blue stragglers formation via Roche lobe overflow, as well as how this can be enhanced for blue stragglers formed in globular clusters.