Period-luminosity-colour relation for early-type contact binaries

Abstract

This work describes the analysis of 64 early-type, massive contact or near-contact eclipsing systems from the Large Magellanic Cloud discovered by the third phase of the Optical Gravitational Lensing Experiment (OGLE-III). It presents the determination of the period- luminosity-colour relation followed by these objects, that is different from the one previously known for late-type W UMa stars. The relation for massive stars has a significantly steeper dependence on the colour, which is related to a much higher bolometric correction, however it is shallower in the period term. This leads to the conclusion, that the relation for the total population of main-sequence contact binaries is non-linear. When studied separately, genuinely contact and near-contact systems follow two slightly different relations.