Eclipse studies of the dwarf nova HT Cassiopeiae. I - Observations and system parameters

Abstract

Optical eclipses are used to investigate the structure of the dwarf nova HT Cas. We present high-speed multicolor light curves covering four eclipses at UBR in 1982 September and 12 eclipses at UBVR in 1983 November-December. From the latter we derive high-quality mean light curves that cleanly separate the white dwarf and accretion disk eclipses. The bright spot is weak or absent during our observations, but a 0.3 mag orbital modulation, centered on mid-eclipse, is seen in the U-band. We define a purely photometric model of the system using contact timings of the white dwarf from the data presented here and measurements of the bright spot eclipses in other data (published by Patterson in 1981). This model features Mw = 0.61 ± 0.04 M⊙, MR = 0.09 ± 0.02 M⊙ (q = 0.15 ± 0.03), and i = 81° ± 1°. We predict KR = 389 ± 4 km s-1 1.6 σ below the measured value of 430 ± 25 km s-1, from the absorption lines of the secondary star, and Kw = 58 ± 11 km s-1, 4.5 σ below the measured value of 115 ± 6 km s-1 from the accretion disk's emission lines. Based on such comparisons, we find good internal consistency among the available constraints apart from the emission-line radial velocity curves, which are suspect because they are 30° out of phase with the eclipse.