OBSERVATIONS AND ANALYSES OF THE ECCENTRIC ORBIT ECLIPSING BINARY HP DRACONIS

We present results of an analysis of all available data of the double-lined spectroscopic and eclipsing binary HP Draconis. The analyses make use of unpublished radial velocity (RV) and extensive photoelectric photometry data as well as published Hipparcos photometric observations and RV data from Asiago Observatory. The system is eccentric and the current analyses suggest apsidal motion to be present only weakly, but a significant amount of third light is found in all three passbands, B, V, and hip. Relatively high precision has been achieved for the mass and radius among the absolute parameters with fractional error of 0.95% or better: M(1,2) = 1.133 +/- 0.005, 1.094 +/- 0.007 M(circle dot); R(1,2) = 1.371 +/- 0.012, 1.052 +/- 0.010 R(circle dot). Other derived parameters are P = 10.76152 +/- 0.00019 days, a = 26.79 +/- 0.04 R(circle dot), e = 0.0367 +/- 0.0009, omega = 0.693 +/- 0.037, q = 0.966 +/- 004, and Delta T = 105 +/- 5 K. We derive a distance to the system of 77 +/- 3 pc. Comparison with Padova theoretical models for different chemical compositions suggests that the components may be of solar age and roughly solar composition, with the primary component less than half as dense as the secondary component and slightly evolved off the zero-age main sequence.