Constraining Roche-Lobe Overflow Models Using the Hot-Subdwarf Wide Binary Population

TL;DR

This paper investigates the formation of hot subdwarf stars through binary interactions, specifically stable Roche-lobe overflow, by comparing theoretical models with observed wide binary populations to improve understanding of stellar evolution.

Contribution

It presents an analysis of binary population synthesis models for hot subdwarfs and discusses potential improvements to better match observations.

Findings

Identifies key observables for testing RLOF models

Highlights discrepancies between models and observed populations

Proposes refinements to binary interaction assumptions

Abstract

One of the important issues regarding the final evolution of stars is the impact of binarity. A rich zoo of peculiar, evolved objects are born from the interaction between the loosely bound envelope of a giant, and the gravitational pull of a companion. However, binary interactions are not understood from first principles, and the theoretical models are subject to many assumptions. It is currently agreed upon that hot subdwarf stars can only be formed through binary interaction, either through common envelope ejection or stable Roche-lobe overflow (RLOF) near the tip of the red giant branch (RGB). These systems are therefore an ideal testing ground for binary interaction models. With our long term study of wide hot subdwarf (sdB) binaries we aim to improve our current understanding of stable RLOF on the RGB by comparing the results of binary population synthesis studies with the observed population. In this article we describe the current model and possible improvements, and which observables can be used to test different parts of the interaction model.