An Eclipsing Binary Comprising Two Active Red Stragglers of Identical Mass and Synchronized Rotation: A Post-Mass-Transfer System or Just Born That Way?
Keivan G. Stassun (1), Guillermo Torres (2), Marina Kounkel (1),, Benjamin M. Tofflemire (3), Emily Leiner (4), Dax L. Feliz (5), Don M. Dixon, (1), Robert D. Mathieu (6), Natalie Gosnell (7), Michael Gully-Santiago (3), ((1) Vanderbilt University, (2) Harvard-Smithsonian CfA

TL;DR
This paper reports the discovery of an equal-mass eclipsing binary of two active red straggler stars with synchronized rotation, exploring whether their properties result from post-mass-transfer evolution or their initial formation.
Contribution
It presents the first detailed characterization of a red straggler binary with synchronized rotation and discusses possible evolutionary scenarios including mass transfer or initial formation conditions.
Findings
Both stars have nearly identical masses of 1.419 Msun.
Stars show signs of magnetic activity, rapid rotation, and synchronization.
Models with spots can reproduce observed stellar parameters.
Abstract
We report the discovery of 2M0056-08 as an equal-mass eclipsing binary (EB), comprising two red straggler stars (RSSs) with an orbital period of 33.9 d. Both stars have masses of 1.419 Msun, identical to within 0.2%. Both stars appear to be in the early red-giant phase of evolution; however, they are far displaced to cooler temperatures and lower luminosities compared to standard stellar models. The broadband spectral energy distribution shows NUV excess and X-ray emission, consistent with chromospheric and coronal emission from magnetically active stars; indeed, the stars rotate more rapidly than typical red giants and they evince light curve modulations due to spots. These modulations also reveal the stars to be rotating synchronously with one another. There is evidence for excess FUV emission and long-term modulations in radial-velocities; it is not clear whether these are also…
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Taxonomy
TopicsStellar, planetary, and galactic studies · Astronomy and Astrophysical Research · Astro and Planetary Science
