Variability, periodicity, and contact binaries in WISE

The time-series component of Wide-field Infrared Survey Explorer (WISE) is a valuable resource for the study of variable objects. We present an analysis of an all-sky sample of similar to 450 000 AllWISE+NEOWISE infrared light curves of likely variables identified in AllWISE. By computing periodograms of all these sources, we identify similar to 56000 periodic variables. Of these, similar to 42000 are short-period (P < 1 d), near-contact, or contact eclipsing binaries, many of which are on the main sequence. We use the periodic and aperiodic variables to test computationally inexpensive methods of periodic variable classification and identification, utilizing various measures of the probability distribution function of fluxes and of time-scales of variability. The combination of variability measures from our periodogram and non-parametric analyses with infrared colours from WISE and absolute magnitudes, colours, and variability amplitude from Gaia is useful for the identification and classification of periodic variables. Furthermore, we show that the effectiveness of non-parametric methods for the identification of periodic variables is comparable to that of the periodogram but at a much lower computational cost. Future surveys can utilize these methods to accelerate more traditional time-series analyses and to identify evolving sources missed by periodogram-based selections.