Only a few well characterized very low-mass M dwarfs are known today. Our understanding of M dwarfs is vital as these are the most common stars in our solar neighborhood. We aim to characterize the properties of a rare F+dM stellar system for a better understanding of the low-mass end of the Hertzsprung-Russel diagram. We used photometric light curves and radial velocity follow-up measurements to study the binary. Spectro- scopic analysis was used in combination with isochrone fitting to characterize the primary star. The primary star is an early F-type main-sequence star with a mass of (1.493 +- 0.073) Msun and a radius of (1.474 +- 0.040) Rsun. The companion is an M dwarf with a mass of (0.188 +- 0.014) Msun and a radius of (0.234 +- 0.009) Rsun. The orbital period is (1.35121 +- 0:00001)d. The secondary star is among the lowest-mass M dwarfs known to date. The binary has not reached a 1:1 spin-orbit synchronization. This indicates a young main-sequence binary with an age below ~250 Myrs. The mass-radius relation of both components are in agreement with this finding.
@article{arxiv.1602.01575,
title = {An M dwarf Companion to an F-type Star in a young main-sequence binary},
author = {Ph. Eigmüller and J. Eislöffel and Sz. Csizmadia and H. Lehmann and A. Erikson and M. Fridlund and M. Hartmann and A. Hatzes and Th. Pasternacki and H. Rauer and A. Tkachenko and H. Voss},
journal= {arXiv preprint arXiv:1602.01575},
year = {2016}
}