We present the discovery of NGTS J214358.5-380102, an eccentric M-dwarf binary discovered by the Next Generation Transit Survey. The system period of 7.618 days is greater than many known eclipsing M-dwarf binary systems. Its orbital eccentricity of 0.323−0.0037+0.0014, is large relative to the period and semi-major axis of the binary. Global modelling of photometry and radial velocities indicate stellar masses of MA=0.426−0.0049+0.0056, MB=0.455−0.0052+0.0058 and stellar radii RA=0.461−0.025+0.038RB=0.411−0.039+0.027, respectively. Comparisons with stellar models for low mass stars show that one star is consistent with model predictions whereas the other is substantially oversized. Spectral analysis of the system suggests a primary of spectral type M3V, consistent with both modelled masses and radii, and with SED fitting of NGTS photometry. As the most eccentric eclipsing M-dwarf binary known, NGTS J214358.5-380102 provides an interesting insight into the strength of tidal effects in the circularisation of stellar orbits.
@article{arxiv.2003.14314,
title = {NGTS J214358.5-380102 -- NGTS discovery of the most eccentric known eclipsing M-Dwarf binary system},
author = {Jack S. Acton and Michael R. Goad and Liam Raynard and Sarah L. Casewell and James A. G. Jackman and Richard D. Alexander and David R. Anderson and Daniel Bayliss and Edward M. Bryant and Matthew R. Burleigh and Claudia Belardi and Benjamin F. Cooke and Phillip Eigmüller and Samuel Gill and James S. Jenkins and Monika Lendl and Tom Louden and James McCormac and Maximiliano Moyano and Louise D. Nielsen and Rosanna H. Tilbrook and Stéphane Udry and Christopher A. Watson and Richard G. West and Peter J. Wheatley and Jose I. Vines},
journal= {arXiv preprint arXiv:2003.14314},
year = {2020}
}