The ROSAT Bright Source 1RXS J201607.0+251645: An Active Algol-type Binary

1RXS J201607.0+251645 is identified to be an eclipsing binary. We present the preliminary observations in V band with the 0.6-m telescope for three years and the extensive observations in V and R band with the 0.8-m telescope for six nights, respectively. The light curve of the system is EB type. Five light minimum times were obtained and the orbital period of 0. 388058(±0. 00044) is determined. The photometric solution given by the 2003-version Wilson-Devinney program suggests the binary is a semi-detached system with the photometric mass ratio 0.895(±0.006), which probably comprises a G5 primary and an oversize K5 secondary. The less massive component has completely filled its Roche lobe, while the other almost fills its Roche lobe with the filling factor of 93.4%. The system shows a varying O’Connell effect in its phase folded diagrams from 2005 to 2007, and is X-ray luminous with logLX/Lbol ∼ −3.27. Possible mechanisms to account for these two phenomena are discussed. Finally, we infer the binary may be in thermal oscillation or may evolve into a contact binary.