Absolute properties of RU Cnc revisited: An active RS CVn-type eclipsing binary with a red giant branch and a main sequence components

Abstract

We present observations and analysis of an RS CVn-type double-lined eclipsing binary system, RU Cnc. The system has been observed for over a century. The high-quality long-cadence \emph{Kepler} K2 C5 and C18, newly obtained observations, and two radial velocity curves were combined and analyzed simultaneously assuming multi-spot model. The masses, radii and luminosities of the component stars are precisely obtained as $M_\textrm{c} = 1.386\pm0.044\, M_{_\odot}$, $M_\textrm{h} = 1.437 \pm 0.046\, M{_\odot}$, $R_\textrm{h} = 2.39\pm 0.07\, R{_\odot}$, $R_\textrm{c} = 5.02 \pm 0.08\, R{_\odot}$, $L_\textrm{h} = 11.4\pm 1.2\, L{_\odot}$, $L_\textrm{c} = 12.0 \pm 1.0\, L{_\odot}$ and with a separation of $\textrm{a} = 27.914 \pm 0.016\, R{_\odot}$. The distance of the system is determined to be $380\pm 57\,$ pc which is consistent with the Gaia DR2 result. Long-term detailed period variation analysis of the system indicate a period decrease of $7.9\times10^{-7}$ days per year. The results suggest the cooler component to be on the red giant branch (RGB) and the hotter one to be still on the main sequence.