Population Synthesis of Hot Subdwarfs: A Parameter Study

TL;DR

This study conducts a comprehensive parameter analysis of binary population synthesis models to understand the formation and characteristics of hot subdwarf binaries, comparing model predictions with observed populations.

Contribution

It introduces a detailed grid of binary evolution models with varied assumptions, exploring their impact on the predicted hot subdwarf populations and matching observations.

Findings

Multiple parameter sets can reproduce observed sdB binary subpopulations.

Period distribution of sdB + early F dwarf binaries provides insights into mass transfer scenarios.

Model assumptions significantly influence the predicted population characteristics.

Abstract

Binaries that contain a hot subdwarf (sdB) star and a main sequence companion may have interacted in the past. This binary population has historically helped determine our understanding of binary stellar evolution. We have computed a grid of binary population synthesis models using different assumptions about the minimum core mass for helium ignition, the envelope binding energy, the common envelope ejection efficiency, the amount of mass and angular momentum lost during stable mass transfer, and the criteria for stable mass transfer on the red giant branch and in the Hertzsprung gap. These parameters separately and together can significantly change the entire predicted population of sdBs. Nonetheless, several different parameter sets can reproduce the observed subpopulation of sdB + white dwarf and sdB + M dwarf binaries, which has been used to constrain these parameters in previous studies. The period distribution of sdB + early F dwarf binaries offers a better test of different mass transfer scenarios for stars that fill their Roche lobes on the red giant branch.