Statistical Analysis of the OGLE Collection of Eclipsing Binaries: Temperature Ratio of A-type Contact Binary Systems
Abstract
A contact binary star system consists of two stars orbiting each other so closely that they share a common atmosphere. Binnendijk (1970) divided contact binaries into W and A-types based on the relative depths of the eclipses. W-types show a shallower eclipse when the smaller (and hence less massive) star is in front, while A-types show the reverse. This is interpreted to mean the smaller star is warmer (temperature ratio > 1) for W type and cooler (temperature ratio < 1) for A type, although the cause for difference of either sort is not known. We explored the statistical properties of these two subtypes through an analysis of the OGLE collection of eclipsing binaries. Soszynski et al. (2016) presented an astonishing 450,000 eclipsing and ellipsoidal variables from the OGLE survey. From this sample we selected 184,000 likely contact binary systems based on light curve shape. We computed a grid of PHOEBE contact binary light curves as a function of mass ratio, fillout factor, temperature ratio, and inclination angle. We performed least squares fits to the entire sample to determine the statistical distribution of these four physical parameters. (The strength of third light and time of zero orbital phase were also fit, although these change the scale and zero time of the light curve, not the shape.) Plotting our results as a function of orbital period confirm earlier findings that A-types dominate longer periods. The large extent of the catalog allows us to extend those findings out to periods of 1.4 days. We also find that mass ratios are relatively and fillout factors very high for A types. We correct the temperature ratio for gravity darkening and find typical corrected ratios are nearly unity. This makes sense given the deep contact indicated by large fillout factors. This work was supported by NSF grant 1716622. L. Binnendijk 1970, Vistas in Astronomy, 12, 217. I. Soszynski. et al. 2016, Acta Astronomica, 66, 405.
- Publication:
-
American Astronomical Society Meeting Abstracts #235
- Pub Date:
- January 2020
- Bibcode:
- 2020AAS...23511406B