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.
@article{arxiv.2208.10534,
title = {The EBLM project X. Benchmark masses, radii and temperatures for two fully convective M-dwarfs using K2},
author = {Alison Duck and David V. Martin and Sam Gill and Tayt Armitage and Romy Rodríguez Martínez and Pierre F. L. Maxted and Daniel Sebastian and Ritika Sethi and Matthew I. Swayne and Andrew Collier Cameron and Georgina Dransfield and B. Scott Gaudi and Michael Gillon and Coel Hellier and Vedad Kunovac and Christophe Lovis and James McCormac and Francesco A. Pepe and Don Pollacco and Lalitha Sairam and Alexandre Santerne and Damien Ségransan and Matthew R. Standing and John Southworth and Amaury H. M. J. Triaud and Stephane Udry},
journal= {arXiv preprint arXiv:2208.10534},
year = {2024}
}