The EBLM project X. Benchmark masses, radii and temperatures for two fully convective M-dwarfs using K2

TL;DR

This study presents precise measurements of two fully convective M-dwarfs using K2 data, highlighting the importance of model uncertainties in stellar parameter determination.

Contribution

The paper provides benchmark masses, radii, and temperatures for two M-dwarfs and assesses the impact of model uncertainties on these measurements.

Findings

Masses measured with better than 5% precision

Radii determined with better than 3% precision

Model uncertainty is comparable to statistical uncertainty

Abstract

M-dwarfs are the most abundant stars in the galaxy and popular targets for exoplanet searches. However, their intrinsic faintness and complex spectra inhibit precise characterisation. We only know of dozens of M-dwarfs with fundamental parameters of mass, radius and effective temperature characterised to better than a few per cent. Eclipsing binaries remain the most robust means of stellar characterisation. Here we present two targets from the Eclipsing Binary Low Mass (EBLM) survey that were observed with K2: EBLM J0055-00 and EBLM J2217-04. Combined with HARPS and CORALIE spectroscopy, we measure M-dwarf masses with precisions better than 5%, radii better than 3% and effective temperatures on order 1%. However, our fits require invoking a model to derive parameters for the primary star. By investigating three popular models, we determine that the model uncertainty is of similar magnitude to the statistical uncertainty in the model fits. Therefore, whilst these can be considered benchmark M-dwarfs, we caution the community to consider model uncertainty when pushing the limits of precise stellar characterisation.