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Published February 10, 2011 | Published
Journal Article Open

The Mass-Radius(-Rotation?) Relation for Low-mass Stars


The fundamental properties of low-mass stars are not as well understood as those of their more massive counterparts. The best method for constraining these properties, especially masses and radii, is to study eclipsing binary systems, but only a small number of late-type (≥M0) systems have been identified and well characterized to date. We present the discovery and characterization of six new M dwarf eclipsing binary systems. The 12 stars in these eclipsing systems have masses spanning 0.38-0.59 M_⊙ and orbital periods of 0.6-1.7 days, with typical uncertainties of ~0.3% in mass and ~0.5%-2.0% in radius. Combined with six known systems with high-precision measurements, our results reveal an intriguing trend in the low-mass regime. For stars with M = 0.35-0.80 M_⊙, components in short-period binary systems (P ≲ 1 day; 12 stars) have radii which are inflated by up to 10% (μ = 4.8% ± 1.0%) with respect to evolutionary models for low-mass main-sequence stars, whereas components in longer-period systems (> 1.5 days; 12 stars) tend to have smaller radii (μ = 1.7% ± 0.7%). This trend supports the hypothesis that short-period systems are inflated by the influence of the close companion, most likely because they are tidally locked into very high rotation speeds that enhance activity and inhibit convection. In summary, very close binary systems are not representative of typical M dwarfs, but our results for longer-period systems indicate that the evolutionary models are broadly valid in the M ~ 0.35-0.80 M_⊙ regime.

Additional Information

© 2011 American Astronomical Society. Received 2010 August 13; accepted 2010 November 5; published 2011 January 19. The authors thank C. Slesnick, G. Herczeg, A.M. Cody, M. Ireland, M. Liu, T. Dupuy, J. Johnson, T. Boyajian, M. López- Morales, and K. Stassun for helpful discussions and suggestions, as well as Mansi Kasliwal for her assistance in scheduling the observations with the Palomar 60" telescope. They also thank the anonymous referee for providing a prompt and helpful review. The analysis in this paper used two existing data analysis pipelines, MAKEE by Tom Barlow and BFall by Slavek Rucinski; the authors gratefully acknowledge their contribution to the field by developing and supporting this software. Some of the data products for this project were provided by a collaboration between the Global Network of Astronomical Telescopes, Inc., and the Moving Object and Transient Event Search System. This work also makes use of data products from 2MASS, which is a joint project of the University of Massachusetts and IPAC/Caltech, funded by NASA and the NSF. A.L.K. was supported by NASA through Hubble Fellowship grant 51257.01 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555. This research was partially supported by a grant to GNAT, Inc., from the American Astronomical Society.

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August 19, 2023
October 23, 2023