A short-period binary OGLE-BLG-ELL-006503 showing slow variations in brightness

TL;DR

This study analyzes 28 years of data on a binary star system, revealing long-term brightness variations likely caused by large stellar spots and orbital period changes linked to magnetic activity.

Contribution

It provides the first detailed long-term analysis of brightness and orbital variations in the binary OGLE-BLG-ELL-006503, highlighting magnetic activity effects.

Findings

Brightness variations are driven by large photospheric spots.

Orbital period change suggests mass redistribution and magnetic reconfiguration.

System likely consists of late-type, tidally-deformed stars.

Abstract

Analysis of 28 years of OGLE project data for the 0.404 day period binary OGLE BLG ELL-006503 (V1231 Sco) shows a superposition of tidal-interaction variations of about 0.07 magnitude in the I-band onto a time-scale 5-10 year, 0.15-0.17 magnitude brightness drift. Seasonal light-curves suggest that this long-term variability is driven by large photospheric spots (approx 0.3 stellar radii) that exhibit a tendency to orient themselves relative to the tidal interaction line. The eclipse time O-C residuals reveal an orbital period change characterized by a timescale of approximately 2x10^6 years, suggesting a mild mass redistribution, potentially linked to global magnetic fields reconfiguration. Gaia parallax and absolute magnitude estimates indicate a system consisting of solar-type stars. The lack of eclipses and extreme spot activity suggest the binary may consist of late-type, tidally-deformed stars rather than a typical W UMa-type system.