T-Lyr1-17236: A Long-Period Low-Mass Eclipsing Binary

TL;DR

This paper reports the discovery of a long-period low-mass eclipsing binary system, which serves as a crucial test case for understanding the mass-radius discrepancy in low-mass stars and the role of magnetic activity.

Contribution

It presents the first well-characterized long-period low-mass eclipsing binary, offering new insights into stellar magnetic activity's impact on stellar models.

Findings

System has a 8.4-day orbital period with component masses of 0.68 and 0.52 solar masses.

Preliminary properties suggest consistency with current stellar models.

Longer period implies weaker magnetic activity, supporting the magnetic activity hypothesis.

Abstract

We describe the discovery of a 0.68+0.52 solar mass eclipsing binary (EB) with an 8.4-day orbital period, found through a systematic search of ten fields of the Trans-atlantic Exoplanet Survey (TrES). Such long-period low-mass EBs constitute critical test cases for resolving the long standing discrepancy between the theoretical and observational mass-radius relations at the bottom of the main sequence. It has been suggested that this discrepancy may be related to strong stellar magnetic fields, which are not properly accounted for in current theoretical models. All previously well-characterized low-mass main sequence EBs have periods of a few days or less, and their components are therefore expected to be rotating rapidly as a result of tidal synchronization, thus generating strong magnetic fields. In contrast, the binary system described here has a period that is over three times longer than previously characterized low-mass main sequence EBs, and its components rotate relatively slowly. It is therefore expected to have a weaker magnetic field and to better match the assumptions of theoretical stellar models. Our follow-up observations of this EB yield preliminary stellar properties that suggest it is indeed consistent with current models. If further observations confirm a low level of activity in this system, these determinations would provide support for the hypothesis that the mass-radius discrepancy is at least partly due to magnetic activity.