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

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. High-quality long-cadence observations, newly obtained from the Kepler K2 C5 and C18 campaigns, and two radial velocity curves were combined and analysed simultaneously, assuming a multispot model. The masses, radii and luminosities of the component stars have been precisely obtained as , , , , and, with a separation of . The distance of the system is determined to be pc, which is consistent with the Gaia Data Release 2 result. Long-term detailed period variation analysis of the system indicates a period decrease of 7.9x10(-7) d yr(-1). The results suggest that the cooler component is on the red giant branch (RGB) and the hotter component is still on the main sequence.