The eclipsing LMC star OGLE05155332--6925581: a clue for Double Periodic Variables

TL;DR

This paper studies the binary star OGLE05155332--6925581, revealing it as a semi-detached system with a circumbinary disc, exhibiting complex variability, mass transfer, and long-term periodicity, characteristic of Double Periodic Variables in the Magellanic Clouds.

Contribution

It provides detailed modeling and analysis of OGLE05155332--6925581, identifying its nature as a semi-detached binary with a circumbinary disc and long-term variability mechanisms, advancing understanding of DPVs.

Findings

Binary is semi-detached with mass transfer from less to more massive star.

Presence of a luminous circumprimary disc and Hα emission.

Long cycle variability is circumbinary and not eclipsed.

Abstract

We investigate the nature of OGLE05155332-6925581, one of the brightest members of the enigmatic group of Double Periodic Variables (DPVs) recently found in the Magellanic Clouds. The modeling of archival orbital light curves (LCs), along with the analysis of the radial velocities suggest that this object is a semi--detached binary with the less massive star transferring matter to the more massive and less evolved star, in an Algol--like configuration. We find evidence for additional orbital variability and H$\alpha$ emission, likely caused by an accretion disc around the primary star. As in the case of $\beta Lyr$ the circumprimary disc seems to be more luminous than the primary, but we do not detect orbital period changes. We find that the LC follows a loop in the color--magnitude diagram during the long cycle; the system is redder when brighter and the rising phase is bluer than during decline. Infrared excess is also present. The source of the long--term periodicity is not eclipsed, indicating its circumbinary origin. Strong asymmetries, discrete absorption components (DACs) and a $\gamma$ shift are new and essential observational properties in the infrared H I lines. The DACs strength and RV follow a saw--teeth pattern during the orbital cycle. We suggest that the system experiences supercycles of mass outflow feeding a circumbinary disc. Mass exchange and mass loss could produce comparable but opposite effects in the orbital period on a long time scale, resulting in a quasi--constancy of this parameter.