A new sample of massive B-type contact binary candidates from the OGLE survey of the Magellanic Clouds

TL;DR

This study significantly expands the known sample of massive B-type contact binaries in the Magellanic Clouds by analyzing OGLE survey data, providing new insights into their properties and evolutionary states.

Contribution

It introduces a large, well-characterized sample of massive B-type contact binary candidates, derived from OGLE data, and compares observations with theoretical models to understand their evolution.

Findings

Identified 37 bona fide contact binary candidates in the Magellanic Clouds.

Most systems are B-type with periods around 0.6-1 days.

Sample matches predictions from MESA binary evolution models.

Abstract

Massive contact binaries (CBs) are key to understanding close-binary evolution and stellar mergers, yet their study has been limited by the scarcity of observed systems, particularly of B-type binaries expected to dominate this class. We bridge this gap by mining a large sample of massive CB candidates from the OGLE-IV database, increasing their known numbers in the Magellanic Clouds by nearly an order of magnitude. Using main-sequence colour-magnitude limits, an observationally informed period-luminosity-colour relation for CBs, and a high morph-parameter cut ($c\geq0.7$), we identified 68 O- and B-type binaries that exhibit smooth, sinusoidal light curves with nearly equal eclipse depths. We then isolated a bona fide sample of 37 CB candidates (28 in the LMC and 9 in the SMC) that match theoretical colour-magnitude and period distributions derived from an extensive grid of MESA binary models. The bona fide sample, dominated by B-type systems with $P\approx0.6-1$ d, agrees with the predicted population and may contain many $q\approx1$ binaries, as expected from models showing mass equalization preceding temperature equalization during nuclear-timescale contact. Synthetic PHOEBE light curves of contact and near-contact phases of MESA models reveal a degeneracy between these configurations, suggesting possible misidentifications among these systems. Spectroscopic follow-up is required to test these predictions and refine the evolutionary framework of massive CBs.