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

Abstract

We present an unbiased orbit solution and mass determination of the components of the eclipsing binary NY Vir as a critical test for the formation scenarios of subdwarf B stars. We obtained high-resolution time series VLT/UVES spectra and high-speed multicolour VLT/ULTRACAM photometric observations of NY Vir, a rapidly pulsating subdwarf B star in a short period eclipsing binary. 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 $\alpha$-formalism. These two models have an sdB primary of 0.466 \msol and 0.389 \msol, respectively. Finally, we report the detection of the Rossiter-McLaughlin effect for NY Vir.