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arXiv · 2410.16427

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

Athira Menon·Michal Pawlak·Daniel J. Lennon·Koushik Sen·Norbert Langer
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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.

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Athira Menon, Michal Pawlak, Daniel J. Lennon, Koushik Sen, Norbert Langer. 2024-10-21. A new sample of massive B-type contact binary candidates from the OGLE survey of the Magellanic Clouds. https://doi.org/10.1051/0004-6361%2F202452694

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