The EBLM project III. A Saturn-size low-mass star at the hydrogen-burning limit

Abstract

We report the discovery of an eclipsing binary system with mass-ratio q $\sim$ 0.07. After identifying a periodic photometric signal received by WASP, we obtained CORALIE spectroscopic radial velocities and follow-up light curves with the Euler and TRAPPIST telescopes. From a joint fit of these data we determine that EBLM J0555-57 consists of a sun-like primary star that is eclipsed by a low-mass companion, on a weakly eccentric 7.8-day orbit. Using a mass estimate for the primary star derived from stellar models, we determine a companion mass of $85\pm 4M_{\mathrm{Jup}}$ ($0.081M_{\odot }$) and a radius of $0.84_{-0.04}^{+0.14}{R}_{\mathrm{Jup}}$ ($0.084R_{\odot }$) that is comparable to that of Saturn. EBLM J0555-57Ab has a surface gravity $\log g_2=5.50_{-0.13}^{+0.03}$ and is one of the densest non-stellar-remnant objects currently known. These measurements are consistent with models of low-mass stars.

arXiv commentAccepted for publication in A&A, 6 pages, 5 figures

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