Mass ratio estimates for overcontact binaries using the derivatives of light curves. II. Systems with deep eclipses

Abstract This is the second paper that proposes a simple method for estimating mass ratios using the derivatives of light curves for overcontact binaries. In the first paper (Kouzuma 2023, ApJ, 958, 84), we presented a method to estimate the mass ratios for systems exhibiting a double-peak feature in the second derivatives of their light curves around eclipses. This second paper focuses on overcontact systems that are not addressed in the first paper, that is, systems lacking a double peak in the second derivative. A sample of synthetic light curves for overcontact binaries consists of 89670, covering a parameter space typical of overcontact systems. On the basis of a recent study that proposed a new classification scheme using light-curve derivatives up to the fourth order, the sample light curves were classified. We found that time intervals between two local extrema in the derivatives are associated with the mass ratio in systems that exhibit a high degree of eclipse obscuration. Using regression analysis for the identified associations, we derived empirical formulae to estimate the mass ratio and its associated uncertainty. The application of our proposed method to real overcontact binary data demonstrated its effectiveness in providing reliable estimates for both values.