2020RAA....20...62A

We present the results of our study of the eclipsing binary systems CSS J112237.1+395219, LINEAR 1286561 and LINEAR 2602707 based on new CCD B, V, R_c and I_c complete light curves. The ultra-short period nature of these stars, as reported by Drake et al., is confirmed and the system's periods are revised. The light curves were modeled using the 2003 version of the Wilson-Devinney code. When necessary, cool spots on the surface of the primary component were introduced to account for asymmetries in the light curves. As a result, we found that CSS J112237.1+395219 is a W UMa type contact binary system belonging to W subclass with a mass ratio of q = 1.61 and a shallow degree of contact of 14.8% where the primary component is hotter than the secondary one by 500 K. LINEAR 1286561 and LINEAR 2602707 are detached binary systems with mass ratios q = 3.467 and q = 0.987 respectively. These detached systems are low-mass M-type eclipsing binaries with similar temperatures. The marginal contact, fill-out factor and temperature difference between components of CSS J112237.1+395219 suggest that this system may be at a key evolutionary state predicted by thermal relaxation oscillation (TRO) theory. From the estimated absolute parameters, we conclude that our systems share common properties with other ultra-short period binaries.