Testing Binary Population Synthesis Models with Hot Subdwarfs

TL;DR

This paper evaluates binary star evolution models by comparing predicted populations of hot subdwarfs with observed data, highlighting the potential for discovering hidden populations through wide-field surveys.

Contribution

It introduces a method to distinguish observable and hidden hot subdwarfs in binary systems and assesses the completeness of current catalogs.

Findings

Current catalogs may be incomplete, missing hidden sdB populations.

Wide-field surveys like 2MASS, SDSS, and GALEX can help identify hidden sdBs.

Models successfully explain short-period sdB systems but less so for long-period ones.

Abstract

Models of binary star interactions have been successful in explaining the origin of field hot subdwarf (sdB) stars in short period systems, but longer-period systems that formed via Roche-lobe overflow (RLOF) mass transfer from the present sdB to its companion have received less attention. We map sets of initial binaries into present-day binaries that include sdBs and main-sequence stars, distinguishing "observable" sdBs from "hidden" ones. We aim to find out whether (1) the existing catalogues of sdBs are sufficiently fair samples of all the kinds of sdB binaries that theory predicts; or instead whether (2) large predicted hidden populations mandate the construction of new catalogues, perhaps using wide-field imaging surveys such as 2MASS, SDSS, and Galex. We also report on a pilot study to identify hidden subdwarfs, using 2MASS and GALEX data.