The M-dwarf Ultraviolet Spectroscopic Sample I. Determining Stellar Parameters for Field Stars

TL;DR

This paper introduces a Bayesian framework for accurately determining fundamental parameters of M-dwarf stars using empirical calibrations, and applies it to a new ultraviolet spectroscopic sample to study stellar structure transitions.

Contribution

It presents a novel Bayesian method for simultaneous stellar parameter estimation and introduces the MUSS sample for low-mass stars with UV data.

Findings

New M-dwarf mass-radius relation with 3.1% scatter.

Defined a low-mass main sequence in the solar neighborhood.

Identified the transition point from fully to partly convective interiors at 0.337 M_sun.

Abstract

Accurate stellar properties are essential for precise stellar astrophysics and exoplanetary science. In the M-dwarf regime, much effort has gone into defining empirical relations that can use readily accessible observables to assess physical stellar properties. Often, these relations for the quantity of interest are cast as a non-linear function of available data; however, in Bayesian modeling the reverse is needed. In this article, we introduce a new Bayesian framework to self-consistently and simultaneously apply multiple empirical calibrations to fully characterize the mass, luminosity, radius, and effective temperature of a field age M-dwarf. This framework includes a new M-dwarf mass-radius relation with a scatter of 3.1% at fixed mass. We further introduce the M-dwarf Ultraviolet Spectroscopic Sample (MUSS), and apply our methodology to provide consistent stellar parameters for these nearby low-mass stars, selected as having available spectroscopic data in the ultraviolet. These targets are of interest largely as either exoplanet hosts or benchmarks in multi-wavelength stellar activity. We use the field MUSS stars to define a low-mass main sequence in the solar neighborhood through Gaussian Process (GP) regression. These results enable us to empirically measure a feature in the GP derivative at $\mathcal{M}_{b} = 0.337 \pm ^{0.013}_{0.026}$ $M_{\odot}$ that indicates where the M-dwarf Ultraviolet Spectroscopic Sample transitions from fully to partly convective interiors.