Comprehensive Photometric Investigation of an Active Early K-type Contact System -- IL Cnc

TL;DR

This study provides a detailed photometric and spectroscopic analysis of the active early K-type contact binary IL Cnc, revealing its physical parameters, activity features, and orbital period variations, contributing to understanding K-type contact systems.

Contribution

It offers the first comprehensive analysis combining ground-based and Kepler data, and refines the system's physical parameters including mass ratio, contact degree, and activity indicators.

Findings

System is a highly active W-subtype K-type contact binary.

Mass ratio determined as 1.76±0.05, with components in shallow contact.

Orbital period shows sinusoidal variation likely due to starspot activity.

Abstract

Comprehensive photometric investigation was carried out to the early K-type contact binary - IL Cnc. 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 effect 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 $M_2/M_1 = 1.76\pm 0.05$. The components are in shallow contact ($f\sim 9\%$) and have a temperature difference about $T_2 - T_1 = -280\pm 20$ 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$_{sun}$ and $M_2\sim 0.90$ M$_{sun}$. 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 H$\alpha$ 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)s of the primary minima show sinusoidal variation while the secondary do not. The oscillation is more likely to be caused by the starspot activities. Yet this assumption needs more data to support.