Absolute Properties of the Main-Sequence Eclipsing Binary Star BP Vulpeculae

Abstract

We present 5236 differential observations in the V filter measured by a robotic telescope, as well as radial velocities from spectroscopic observations, of the detached, eccentric 1.9 day double-lined eclipsing binary star BP Vul. Absolute dimensions of the components are determined with high precision (better than 1% in the masses and radii) for the purpose of testing various aspects of theoretical modeling. We obtain 1.737 ± 0.015 M⊙ and 1.852 ± 0.014 R⊙ for the primary, and 1.408 ± 0.009 M⊙ and 1.489 ± 0.014 R⊙ for the secondary. The effective temperatures and interstellar reddening of the stars are accurately determined from uvbyβ photometry: 7700 ± 150 K for the primary, 6800 ± 150 K for the secondary—corresponding to spectral types of A7m and F2m—and 0.022 mag for Eb-y. The metallic-lined character of the stars is revealed by high-resolution spectroscopy and uvbyβ photometry. Spectral line widths give rotational velocities that are synchronous with the orbital motion for the secondary component, but subsynchronous for the primary component, in a slightly eccentric orbit (e = 0.0345). Apsidal motion based on times of minimum light appears to be negative with a period of about 75 years based on recent observations of minima, but this result is not confirmed by the radial velocity measurements, and it is indeterminate when older photographic and visual data are included. The components of BP Vul are main-sequence stars with an age of about 1 Gyr according to models.