A rare reflection effect eclipsing sdB plus 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 86.6A degrees. The derived primary mass for 2M 1533+3759, 0.376 +/- 0.055 M (aS (TM)), is significantly lower than the canonical mass (0.48 M (aS (TM))) found for most previously investigated sdB stars. This implies an initial progenitor mass > 1.8 M (aS (TM)), at least a main sequence A star and perhaps even one massive enough to undergo non-degenerate helium ignition.