Cool subdwarfs are metal-poor low-mass stars that formed during the early stages of the evolution of our Galaxy. Because they are relatively rare in the vicinity of the Sun, we know of few cool subdwarfs in the solar neighbourhood, and none with both the mass and the radius accurately determined. This hampers our understanding of stars at the low-mass end of the main-sequence. Here we report the discovery of SDSSJ235524.29+044855.7 as an eclipsing binary containing a cool subdwarf star, with a white dwarf companion. From the light-curve and the radial-velocity curve of the binary we determine the mass and the radius of the cool subdwarf and we derive its effective temperature and luminosity by analysing its spectral energy distribution. Our results validate the theoretical mass-radius-effective temperature-luminosity relations for low-mass low-metallicity stars.
@article{arxiv.1903.02897,
title = {Accurate mass and radius determinations of a cool subdwarf in an eclipsing binary},
author = {Alberto Rebassa-Mansergas and Steven G. Parsons and Vikram S. Dhillon and Juanjuan Ren and Stuart P. Littlefair and Thomas R. Marsh and Santiago Torres},
journal= {arXiv preprint arXiv:1903.02897},
year = {2019}
}