On the accretion disc and evolutionary stage of beta Lyrae

TL;DR

This study models beta Lyrae's light curve considering stellar components and an accretion disc, revealing its evolutionary stage, physical parameters, and mass transfer dynamics, consistent with a quasi-conservative mass exchange in a rapid transfer phase.

Contribution

It provides a detailed physical and evolutionary model of beta Lyrae, including the accretion disc structure and mass transfer rate, based on light curve fitting and comparison with evolutionary models.

Findings

System is at 23 million years, in rapid mass transfer phase.

Mass transfer rate is approximately 1.58 x 10^-5 Msun/year.

The accretion disc contributes 22% to the V-band light at quadrature.

Abstract

We modeled the V-band light curve of beta Lyrae with two stellar components plus an optically thick accretion disc around the gainer assuming a semidetached configuration. We present the results of this calculation, giving physical parameters for the stars and the disc, along with general system dimensions. We discuss the evolutionary stage of the system finding the best match with one of the evolutionary models of Van Rensbergen et al. According to this model, the system is found at age 2.30E7 years, in the phase of rapid mass transfer, the second one in the life of this binary, in a Case-B mass-exchange stage with dM/dt = 1.58E-5 Msun/year. This result, along with the reported rate of orbital period change and observational evidence of mass loss, suggests that the mass transfer in beta Lyrae, is quasi-conservative. The best model indicates that beta Lyrae finished a relatively large mass loss episode 31400 years ago. The light curve model that best fit the observations has inclination angle i = 81 degree, M1 = 13.2 Msun, M2 = 3.0 Msun, R1 = 6.0 Rsun and R2 = 15.2 Rsun. The disc contributes 22% to the total V-band light curve at quadrature, has a radius of 28.3 Rsun and the outer edge thickness is 11.2 Rsun. The light curve model is significantly better with two bright regions in the disc rim with temperatures 10% and 20% higher than the disc outer edge temperature. We compare our results with earlier studies of this interacting binary.