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

TL;DR

This paper reports the first identification of the eclipsing binary 1RXS J201607.0+251645 as an active Algol-type system, providing detailed photometric analysis, orbital parameters, and discussing its evolutionary status.

Contribution

It presents the first identification and detailed photometric analysis of an active Algol-type binary, including orbital parameters and potential evolutionary pathways.

Findings

Orbital period of 0.388058 days determined.

Binary is semi-detached with a mass ratio of 0.895.

System shows a varying O'Connell effect and is X-ray luminous.

Abstract

1RXS J201607.0251645 is identified to be an eclipsing binary for the first time. 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 0.388058d(0.00044d) 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 comprise a G5 primary and an oversize K5 secondary. The less massive component has completely filled up 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 log(LXLbol)3.27. Possible mechanisms to account for these two phenomena are discussed. Finally, we infer the binary may be in thermal oscillation predicted by thermal relaxation oscillation (TRO) theory or may evolve into a contact binary.