A 0.24+0.18 M double-lined eclipsing binary from the HATSouth survey

Abstract

We report the discovery and characterization of a new M-dwarf binary, with component masses and radii of M<inf>1</inf> = 0.244+0.003<inf>-0.003</inf> M<inf>⊙</inf>, R<inf>1</inf> = 0.261+0.006<inf>-0.009</inf> R<inf>⊙</inf>, M<inf>2</inf> = 0.179+0.002<inf>-0.001</inf> M<inf>⊙</inf>, R<inf>2</inf> = 0.218+0.007<inf>-0.011</inf> R<inf>⊙</inf>, and orbital period of ~4.1 d. The M-dwarf binary HATS551Š027 (LP 837Š20) was identified as an eclipsing binary by the HATSouth survey, and characterized by a series of high-precision photometric observations of the eclipse events, and spectroscopic determinations of the atmospheric parameters and radial velocity orbits. HATS551-027 is one of few systems with both stellar components lying in the fully convective regime of very low mass stars, and can serve as a test for stellar interior models. The radius of HATS551-027A is consistent with models to 1σ, whilst HATS551-027B is inflated by 9 per cent at 2σ significance. We measure the effective temperatures for the two stellar components to be T<inf>eff, 1</inf> = 3190 ± 100 K and T<inf>eff, 2</inf> = 2990 ± 110 K; both are slightly cooler than theoretical models predict, but consistent with other M-dwarfs of similar masses that have previously been studied. We also measure significant H α emission from both components of the binary system, and discuss this in the context of the correlation between stellar activity and the discrepancies between the observed and model temperatures. Show more