KIC 5640750 - Long Period Giant Eclipsing Binary

Kian Jek:

The eclipse seen is truly humongous - we are looking at a 6.7 day eclipse (or approx. 160 hours) with a depth of 6.6%! There appears to be another eclipse right at the end of Q11, with a depth of about 1.8%. Just catching a glimpse of this other eclipse is fortuitous because it allows us to get an estimate of the stellar parameters of this EB.

For a giant EB with a total or annular eclipse, the flat-bottomed eclipse is generally the secondary eclipse, where the secondary is occulted by the giant primary. Since it is deeper than the primary eclipse (the one at the end of the data), we can surmise that the secondary must be brighter than the primary. We don't know what the period is, but it must be >1098 days. A reasonable estimate would be approx. 1300 days or longer, and if the primary is 10.365x Sol, then the secondary could be a 1.45x Rsol, Type F star with a Teff of 6300, with an orbit whose semi-major axis is ~ 3 to 3.5 AU. A binary with this configuration will give the observed depths of 6.67% and 1.8% for the secondary and primary eclipses.

You can track the progress of this eclipsing binary star system here.