TYC 2675-663-1: a newly discovered W UMa system in an active state

¹ University of Cambridge, Institute of Astronomy, Cambridge CB3 0HA, UK e-mail: mcaballe@ast.cam.ac.uk
² Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, USA
³ IEEC (Institut d'Estudis Espacials de Catalunya), Edif. Nexus-104, Gran Capità 2-4, 08034 Barcelona, Spain
⁴ Leiden Observatory, PO Box 9513, 2300 RA Leiden, The Netherlands
⁵ CAB–LAEX (CSIC-INTA), ESAC Campus, PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain

Received: 4 November 2009
Accepted: 27 January 2010

Abstract

Aims. The recently discovered eclipsing binary system TYC 2675-663-1 is an X-ray source and shows properties in the optical that are similar to the W UMa systems, but are somewhat unusual compared to what is seen in other contact binary systems. The goal of this work is to characterize its properties and investigate its nature by means of detailed photometric and spectroscopic observations.

Methods. We have performed extensive V-band photometric measurements with the INTEGRAL satellite along with ground-based multi-band photometric observations, as well as high-resolution spectroscopic monitoring, from which we have measured the radial velocities of the components. These data have been analyzed to determine the stellar properties, including the absolute masses and radii. Additional low-resolution spectroscopy was obtained to investigate spectral features.

Results. From the measured eclipse timings we determine an orbital period for the binary of P = 0.4223576 ± 0.0000009 days. The light-curve and spectroscopic analyses reveal the observations to be well represented by a model of an overcontact system composed of main-sequence F5 and G7 stars (temperature difference of nearly 1000 K), with the possible presence of a third star. Low-resolution optical spectroscopy reveals a complex H_α emission and other features that are not yet understood. The unusually high mass ratio of q = 0.81 ± 0.05 places it in the rare “H” (high mass ratio) subclass of the W UMa systems, which are presumably on their way to coalescence.