The effective temperature -- radius relationship of M-dwarfs

Abstract

M-dwarf stars provide very favourable conditions to find habitable worlds beyond our solar system. The estimation of the fundamental parameters of the transiting exoplanets rely on the accuracy of the theoretical predictions for radius and effective temperature of the host M-dwarf, hence the importance of multiple empirical tests of very low-mass star (VLM) models, the theoretical counterpart of M-dwarfs. Recent determinations of mass, radius and effective temperature of a sample of M-dwarfs of known metallicity have disclosed a supposed discontinuity in the effective temperature-radius diagram corresponding to a stellar mass of about 0.2Mo, that has been ascribed to the transition from partially convective to fully convective stars. In this paper we compare existing VLM models to these observations, and find that theory does not predict any discontinuity at around 0.2Mo, rather a smooth change of slope of the effective temperature-radius relationship around this mass value. The appearance of a discontinuity 5is due to naively fitting the empirical data with linear segments. Also, its origin is unrelated to the transition to fully convective structures. We find that this feature is instead an empirical signature for the transition to a regime where electron degeneracy provides an important contribution to the stellar EOS, and constitutes an additional test of the consistency of the theoretical framework for VLM models.

5 pages, 6 figures, Astronomy and Astrophysics in press

References in corpus (8)

• The Transiting Exoplanet Survey Satellite
• New evolutionary models for pre-main sequence and main sequence low-mass stars down to the hydrogen-burning limit
• A terrestrial planet candidate in a temperate orbit around Proxima Centauri
• How to Constrain Your M Dwarf: measuring effective temperature, bolometric luminosity, mass, and radius
• Updated Electron-Conduction Opacities: The Impact on Low-Mass Stellar Models
• An Earth-sized Planet in the Habitable Zone of a Cool Star
• Reevaluating the Mass-Radius Relation for Low-Mass, Main Sequence Stars
• A discontinuity in the $T_{\mathrm{eff}}$-radius relation of M-dwarfs

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