The binary properties of the pulsating subdwarf B eclipsing binary PG 1336-018 (NY Virginis) ^*

¹ Institute for Astronomy, K.U. Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium e-mail: maja.vuckovic@ster.kuleuven.be
² Department of Astrophysics, Institute of Mathematics, Astrophysics and Particle Physics (IMAPP), Radboud University, 6500 GL Nijmegen, The Netherlands
³ Armagh Observatory, College Hill, Armagh, BT61 9DG Northern Ireland
⁴ Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH, UK
⁵ Department of Physics, University of Warwick, Coventry CV4 7AL, UK

Received: 26 January 2007
Accepted: 24 May 2007

Abstract

Aims. We present an unbiased orbit solution and mass determination of the components of the eclipsing binary PG 1336-018 as a critical test for the formation scenarios of subdwarf B stars.

Methods. We obtained high-resolution time series VLT/UVES spectra and high-speed multicolour VLT/ULTRACAM photometric observations of PG 1336-018, a rapidly pulsating subdwarf B star in a short period eclipsing binary.

Results. Combining the radial velocity curve obtained from the VLT/UVES spectra with the VLT/ULTRACAM multicolour lightcurves, we determined numerical orbital solutions for this eclipsing binary. Due to the large number of free parameters and their strong correlations, no unique solution could be found, only families of solutions. We present three solutions of equal statistical significance, two of which are compatible with the primary having gone through a core He-flash and a common-envelope phase described by the α-formalism. These two models have an sdB primary of 0.466  and 0.389 , respectively. Finally, we report the detection of the Rossiter-McLaughlin effect for PG 1336-018.