  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.
