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Published November 10, 2008 | Published
Journal Article Open

T-Lyr1-17236 : a long-period low-mass eclipsing binary


We describe the discovery of a 0.68+0.52 M⊙ eclipsing binary (EB) with an 8.4 day orbital period, found through a systematic search of 10 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 more than 3 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.

Additional Information

© 2008 The American Astronomical Society. Received 2008 April 4; accepted 2008 July 22. We would like to thank Joel Hartman and Doug Mink for their help in operating a few of the software analysis tools used for this paper, and we would like to thank Sarah Dykstra for her editorial assistance. Valeri Hambaryan provided expert assistance in examining archival ROSAT images of T-Lyr1-17236, for which we are grateful, and we thank the referee for a number of helpful comments that have improved the paper. G. T. acknowledges partial support from NSF grant AST 07-08229 and NASA's MASSIF SIM Key Project (BLF57-04). This research has made use of NASA's Astrophysics Data System Bibliographic Services, as well as the SIMBAD database operated at CDS, Strasbourg, France. This publication also used data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center, California Institute of Technology, and is funded by NASA and the National Science Foundation. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among Caltech, the University of California, and NASA. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.

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