Comprehensive photometric investigation of an active early K-type contact system—IL Cancri

Abstract Comprehensive photometric investigation of the early K-type contact binary IL Cnc was carried out. A few light curves from both ground-based telescopes and the Kepler space telescope were obtained (or downloaded) and then analyzed in detail. They are mostly found to be asymmetric and there are even continuously changing O’Connell effects in the light curves from Kepler K2 data, suggesting the system to be highly active. Using the Wilson–Devinney code (version 2013), photometric solutions were derived and then compared. It is found that the calculation of the mass ratio is easily affected by the spot settings. Combining the radial velocities determined from LAMOST median resolution spectral data, the mass ratio of the binary components is found to be M2/M1 = 1.76 ± 0.05. The components are in shallow contact ($f\sim 9\%$) and have a temperature difference about T2 − T1 = −280 ± 20 K. The system is demonstrated to be W-subtype, which may be a common feature of K-type contact binaries. The masses of the binary components were estimated to be $M_1\sim 0.51\, M_{\odot }$ and $M_2\sim 0.90\, M_{\odot }$. The values are in good agreement with that deduced from the parallax data of Gaia. The results suggest that the primary component lacks luminosity compared with the zero main sequence. The Hα spectral line of the primary component is found to be peculiar. Combining newly determined minimum light times with those collected from literature, the orbital period of IL Cnc is studied. It is found that the (O − C) values of the primary minima show sinusoidal variation while those of the secondary do not. The oscillation is more likely to be caused by the starspot activities, yet this assumption needs more data to support.

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