A rare reflection effect eclipsing sdB+dM binary: 2M 1533+3759

In this paper, we report a rare reflection effect eclipsing sdB+dM binary, 2M 1533+3759. It is the seventh eclipsing sdB+dM binary that has been discovered to date. This system has an orbital period of 0. 16177042 day and a velocity semi-amplitude of 71.1 km s^-1. Using a grid of zero-metallicity NLTE model atmospheres, we derived T_eff=29250 K, log g=5.58 and [He/H]=-2. 37 from spectra taken near the reflection effection minimum. Lightcurve modeling resulted in a system mass ratio of 0. 301 and an orbital inclination angle of 86.6°. The derived primary mass for 2M 1533+3759, 0.376±0.055 M_⊙, is significantly lower than the canonical mass (0.48 M_⊙) found for most previously investigated sdB stars. This implies an initial progenitor mass >1.8 M_⊙, at least a main sequence A star and perhaps even one massive enough to undergo non-degenerate helium ignition.