2000PASP..112.1269T

HS 0907+1902 was recently discovered to be one of a handful of deeply eclipsing dwarf novae with periods longward of the 2-3 hr ``gap.'' This paper presents orbit-resolved spectra and time-series photometry of an eclipse. The apparent velocity amplitude of the M-dwarf secondary is K₂=297±15 km.s^–1. The phase of the radial velocities of the Hα emission-line wings agrees accurately (for once) with the phase of the white dwarf motion deduced from the eclipse, and an estimate of the emission-line velocity amplitude yields K₁=115±7 km.s^–1. The eclipse width is Δφ=0.060±0.005. At face value, these measurements yield mass estimates of M₁=0.99±0.12 M_☉ for the white dwarf and M₂=0.38±0.06 M_☉ for the secondary. The eclipse width and nominal mass ratio constrain the binary inclination i to be 77°.3±0°.9. The influence of systematic uncertainties on these values is discussed; the conclusion that the white dwarf is somewhat more massive than typical field white dwarfs appears to be robust.

The Hα emission-line profile out of eclipse is only slightly double-peaked, but the line shows a strong rotational disturbance in eclipse. Models of the line profile through eclipse using a flat, Keplerian disk do not give a good quantitative match to the observations.