Accretion Disks and Long Cycles in β Lyrae-Type Binaries

R. E. Mennickent

doi:10.3390/galaxies10010015

Abstract

In order to inquire about the nature of the accretion disks formed around the more massive companion in binaries with β Lyrae-type light curves, we review literature presenting some physical and observational properties of these systems. In addition, we inspect the photometric time series of three representative eclipsing systems obtained by the Optical Gravitational Lensing Experiment (OGLE) project during the last decades and compare them with β Lyrae. All these three systems show indications of being semidetached with a more massive B-type component and in a mass transfer stage. They also show long photometric cycles, and two of them show changes in the orbital light curve that can be interpreted in terms of structural changes of the accretion disks, eventually driven by variations in the mass transfer rate.

Highlights

The system β Lyrae is an interesting testbed for models of accretion flows by Rochelobe overflow occurring in intermediate mass semidetached binaries
The first detection of interferometric photospheric tidal distortion due to the Roche lobe filling was reported by Zhao et al [4] in β Lyrae, based on interferometry performed with the Center for High Angular Resolution Astronomy (CHARA) array
The light-curve model is significantly better with two bright regions in the disk rim with temperatures 10 and 20 per cent higher than the disk outer edge temperature [8]. β Lyrae is the prototype of eclipsing binaries classified EB according to the shape of their light curves; unequal minima and rounded inter-eclipses shoulders, a signature of a tidally distorted donor star due to the gravitational interaction of the gainer. β Lyrae is an Algol system from the evolutionary point of view, i.e., a system that has reversed its mass ratio as a result of the mass transfer from the initially more massive star onto the initially less massive star

Summary

Introduction

The system β Lyrae is an interesting testbed for models of accretion flows by Rochelobe overflow occurring in intermediate mass semidetached binaries This binary consists of a B8 II “donor” star transferring mass by a gas stream onto a more massive “gainer” star of probably B-type. The first detection of interferometric photospheric tidal distortion due to the Roche lobe filling was reported by Zhao et al [4] in β Lyrae, based on interferometry performed with the Center for High Angular Resolution Astronomy (CHARA) array These authors detected the thick disk surrounding the gainer in H-band images. Hundreds of β Lyrae-type binaries (i.e., those with EB-type light curves) have been found showing long photometric cycles in extensive surveys of variable stars performed in the Galaxy, the Galactic Bulge, and the Magellanic Clouds; they are often named Double Periodic Variables (DPVs) [23,24,25,26]. Contrary to β Lyrae, the orbital period of most of these systems is relatively constant, suggesting a rather mild mass transfer rate or a compensating loss of angular momentum through winds or equatorial outflows [27,28]

The Po-Pl Relationship

Insights on Disks of Systems Showing β Lyrae-Type Light Curves

Light Curve Models for Individual Systems

H J D -2 4 5 0 0 0 0

Findings

Conclusions