The observed temperature distribution of contact binaries derived from SDSS photometry

Data from the VSX, SDSS DR12, and Gaia DR2 catalogs were combined in order to explore the observed temperature distribution of known contact binaries. Color-temperature relations were applied to calculate the effective temperatures of approximately 20000 binaries and a temperature distribution was built using the results with a precision better than 160 K. The temperature distribution shifts to higher temperatures when increasing the distance of the observed objects. The distribution contains a a previously detected bump in the 6000-7000 K range. It is shown that this second maximum is caused by distant and highly reddened objects that are systematically more luminous than contact binaries in this temperature range. We argue that these objects are other variables, possibly semi-detached binaries, misclassified as contact binaries and that the actual temperature distribution of contact binaries does not contain such a peak.