Changing-Inclination Eclipsing Binary Systems Observed with KELT

A rare subset of eclipsing binary systems are those with observed evidence of changing inclination over time. These systems have a third star causing their orbital evolution, which can be observed as changing eclipse depth over time. There have only been on the order of tens of these changing-inclination eclipsing binary systems identified. Over time, the systems with decreasing eclipse depth will be reclassified as former eclipsing binary systems as the eclipses fade from view, while other systems with previously non-visible eclipses may have newly observed increasing eclipse depths. We examine the light-curves of 10 previously known changing-inclination eclipsing binary systems observed by TESS and the ground-based telescope KELT. Each system presented has 3-9 years of observations from KELT, allowing a comprehensive analysis of the changing eclipse depths in several cases. HS Hya, a system previously analyzed by Davenport et al. 2021, is included in the sample and shows evidence in support of its changing inclination. Other systems’ changing eclipse depths are not as evident, but their variability can be more closely analyzed. We present yearly observations for several systems from KELT that show detectable changing eclipse depths which emphasize a need for continued observation. We find eclipse depths in these systems to be gradually changing over time. This exploration of known inclination-changing systems is a proof of concept for using KELT as a “precovery” resource for studying such systems with space-based facilities like TESS.