OGLE-LMC-ECL-17782 & OGLE-LMC-ECL-11893: Two Binary Star Systems With Anomalous Eclipsing Disks

A search for eclipsing binaries that host discs

Authors:

Meng et al

Abstract:

We search for systems hosting eclipsing discs using a complete sample of eclipsing binaries (EBs); those previously identified in the third phase of the Optical Gravitational Lensing Experiment (OGLE-III). Within a subsample of 2823 high-cadence, high-photometric precision and large eclipsing depth detached EBs previously identified in the Large Magellanic Cloud (LMC), we find that the skewness and kurtosis of the light-curve magnitude distribution within the primary eclipse can distinguish EBs with a complex-shaped eclipse from those without. Two systems with previously identified eclipsing discs (OGLE-LMC-ECL-11893 and OGLE-LMC-ECL-17782) are identified with near zero skewness (|S| < 0.5) and positive kurtosis. No additional eclipsing disc systems were found in the OGLE-III LMC, Small Magellanic Cloud or Galactic Disc EB light curves. We estimate that the fraction of detached early-type LMC EBs (which have a primary with an I-band magnitude brighter than ≃19 mag) that exhibit atypical eclipses and so could host a disc is approximately 1/1000. As circumstellar disc lifetimes are short, we expected to primarily find eclipsing discs around young stars. In addition, as there is more room for a disc in a widely separated binary and because a disc close to a luminous star would be above the dust sublimation temperature, we expected to primarily find eclipsing discs in long-period binaries. However, OGLE-LMC-ECL-17782 is a 13.3 d period B star system with a transient and hot (∼6000 K, ∼0.1 au radius) disc and Scott et al. estimate an age of 150 Myr for OGLE-LMC-ECL-11893. Both discs are unexpected in the EB sample and impel explanation.