Mass-ratio distribution of contact binary stars

Overall, our sample includes about 300 late-type and 200 early-type contact binary candidates. We model the amplitude distribution assuming that mass ratios are described by a power law with an exponent $b$ and a cut off at q_min_. We find q_min_=0.087^+0.024^_-0.015_ for late-type contact binaries with periods longer than 0.3 days.

For late-type binaries with shorter periods, we find q_min_=0.246^+0.029^_-0.046_, but the sample is small. For early type contact binary stars with periods shorter than 1 day, we obtain q_min_=0.030^+0.018^_-0.022_. These results indicate a dependence of q_min_ on the structure of the components and are broadly compatible with previous theoretical predictions.

We do not find any clear trends in b. Our method can be easily extended to large samples of contact binaries from TESS and other space-based surveys.