We report the discovery of an eclipsing binary – HS~0705+6700 – being an sdB star with a faint companion .
From its light curve the orbital period of 8263.87 s , the mass ratio of the system q = 0.28 , the inclination of 84 \aas@@fstack { \circ } 4 and other system parameters are derived .
The companion does not contribute to the optical light of the system except through a strong reflection effect .
The semi-amplitude of the radial velocity curve K _ { 1 } = 85.8 km s ^ { -1 } and a mass function of f ( m ) = 0.00626 M _ { \odot } are determined .
A spectroscopic analysis of the blue spectra results in T _ { eff } = 28 800 K , \log~ { } g = 5.40 , and \log ( n _ { He } / n _ { H } ) = -2.68 .
These characteristics are typical for sdB stars , as is its mass of 0.48 M _ { \odot } .
According to its mass ( 0.13 M _ { \odot } ) and radius ( 0.19 R _ { \odot } ) , the companion is an M dwarf .
The primary is in a core helium burning phase of evolution , and the system must have gone through a common envelope stage when the primary was near the tip of the red giant branch .