Ultra-Short-Period Binary Systems in the OGLE Fields Toward the Galactic Bulge

TL;DR

This paper reports the discovery and classification of 242 ultra-short-period binary stars in the Galactic bulge, including the shortest-period M-dwarf binary known, with implications for binary evolution.

Contribution

It provides a new sample of ultra-short-period binaries, including the shortest-period M-dwarf system, and discusses their potential evolutionary pathways.

Findings

242 ultra-short-period binary systems identified

Shortest-period M-dwarf binary candidate discovered

Classification into contact, HW Vir, and cataclysmic variable candidates

Abstract

We present a sample of 242 ultra-short-period (P < 0.22 d) eclipsing and ellipsoidal binary stars identified in the OGLE fields toward the Galactic bulge. Based on the light curve morphology, we divide the sample into candidates for contact binaries and non-contact binaries. In the latter group we distinguish binary systems consisting of a cool main-sequence star and a B-type subdwarf (HW Vir stars) and candidates for cataclysmic variables, including five eclipsing dwarf novae. One of the detected eclipsing binary systems - OGLE-BLG-ECL-000066 - with the orbital period below 0.1 d, likely consists of M dwarfs in a nearly contact configuration. If confirmed, this would be the shortest-period M-dwarf binary system currently known. We discuss possible evolutionary mechanisms that could lead to the orbital period below 0.1 d in an M-dwarf binary.