The mass-radius relationship for very low mass stars: Four new discoveries from the HATSouth Survey

G. Zhou, D. Bayliss, J. D. Hartman, G. A. Bakos, K. Penev, Z. Csubry, T. G. Tan, A. Jordán, L. Mancini, M. Rabus, R. Brahm, N. Espinoza, M. Mohler-Fischer, S. Ciceri, V. Suc, B. Csák, T. Henning, B. Schmidt

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51 Scopus citations


We report the discovery of four transiting F-M binary systems with companions between 0.1 and 0.2M⊙ in mass by the HATSouth survey. These systems have been characterized via a global analysis of the HATSouth discovery data, combined with high-resolution radial velocities and accurate transit photometry observations. We determined the masses and radii of the component stars using a combination of two methods: isochrone fitting of spectroscopic primary star parameters and equating spectroscopic primary star rotation velocity with spin-orbit synchronization. These new very low mass companions are HATS550- 016B (0.110+0.005 -0.006M⊙, 0.147+0.003 -0.004 R⊙), HATS551-019B (0.17+0.01 -0.01M⊙, 0.18+0.01 -0.01 R⊙), HATS551-021B (0.132+0.014 -0.005M⊙, 0.154+0.006 -0.008 R⊙) and HATS553-001B (0.20+0.01 -0.02M⊙, 0.22+0.01 -0.01 R⊙). We examine our sample in the context of the radius anomaly for fully convective low-mass stars. Combining our sample with the 13 other well-studied very low mass stars, we find a tentative 5 per cent systematic deviation between the measured radii and theoretical isochrone models.

Original languageEnglish (US)
Pages (from-to)2831-2844
Number of pages14
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
StatePublished - Jan 2014

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Binaries
  • Eclipsing - stars
  • Low-mass.


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