QR Andromedae

Lore & Background

QR Andromedae was identified as an eclipsing binary from its light curve, which shows clear eclipsing events where brightness drops from magnitude 12.16 to 13.07, leading to its classification as an Algol variable. Its optical spectrum is peculiar, with strong HeII emission lines, Balmer series, and OVI lines, rather than a typical stellar blackbody. It was one of the super soft X-ray sources discovered by the ROSAT satellite, a rare type observed in the Milky Way.

The system is now commonly accepted to consist of a white dwarf burning matter via nuclear fusion on its surface, sustained by high accretion from a companion star. The companion has a mass between 0.3 and 0.5 solar masses and is thought to be a remnant of a more massive evolved star that fills its Roche lobe. The orbital period is 15.85 hours.

Photographic plates from the Harvard College and Sonneberg observatories have recorded its brightness since the late 19th century. Jochen Greiner and Wolfgang Wenzel constructed a 100-year light curve, finding brightness changes of up to one magnitude on various timescales, proposed to result from unstable mass transfers triggering sporadic hydrogen burning. Eclipses are asymmetrical: ingress is more gradual than egress. The secondary minimum varies in phase and depth, indicating occultation behind a variable part of the disk. Out of eclipse, light flickering is seen, and some observations show a periodicity.

Reader's Guide

QR Andromedae holds significance as the nearest and brightest of the super soft X-ray sources discovered by ROSAT, a rare class in the Milky Way. Its 100-year light curve, constructed by Jochen Greiner and Wolfgang Wenzel from Harvard College and Sonneberg observatory plates, reveals brightness changes of up to one magnitude on various timescales, attributed to unstable mass transfers triggering sporadic hydrogen burning on the white dwarf. The system's asymmetrical eclipses—with gradual ingress and sharper egress—and variable secondary minimum depth and phase indicate that the occultation of the secondary star occurs behind a variable part of the accretion disk. Out-of-eclipse flickering and occasional periodicity further characterize its variability. As an Algol-type eclipsing binary with a white dwarf accreting from a low-mass companion, QR Andromedae provides a nearby laboratory for studying super soft X-ray sources and the dynamics of mass transfer in close binaries.