Period-Luminosity-Colour Relation for Early-Type Contact Binaries

TL;DR

This paper derives a new period-luminosity-colour relation for early-type contact binaries, revealing differences from late-type stars and indicating a non-linear relation for main sequence contact binaries.

Contribution

It presents the first detailed analysis of the period-luminosity-colour relation for massive early-type contact binaries, highlighting differences from late-type stars and separating genuinely-contact from near-contact systems.

Findings

The relation for massive stars has a steeper colour dependence.

The period term in the relation is shallower for these stars.

The overall relation is non-linear for the entire population.

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 OGLE-III survey. 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.