The eclipsing binary star RZ Cassiopeiae^*

II. Spectroscopic monitoring in 2006

¹ Thüringer Landessternwarte Tautenburg, 7778 Tautenburg, Germany e-mail: lehm@tls-tautenburg.de
² Astrophysical Research Center for the Structure and Evolution of the Cosmos, Sejong University, Seoul 143-747, Korea
³ Astronomical Observatory of Odessa National University, Shevchenko Park, Odessa, Ukraine e-mail: davidm@sejong.ac.kr

Received: 17 October 2007
Accepted: 19 December 2007

Abstract

Aims.We test the hypothesis that the oEA star RZ Cas has undergone a transient phase of rapid mass-transfer in 2000/2001.

Methods.We analyze a time series of high-resolution spectra of RZ Cas obtained in 2001 and in 2006 for radial velocity (RV) and line profile variations. Improved orbital solutions are determined using the method of differential corrections. In the RV residuals, after subtracting the orbital solution and low-frequency variations, we search for non-radial pulsations in the high-frequency domain and for an amplitude modulation of the pulsation modes.We model the observed line profiles using a new computer program based on the method of spectroscopic eclipse mapping and investigate the line intensity residuals and the Rossiter-McLaughlin effect.

Results.Between 2001 and 2006, the derived orbital solutions show an increase of the orbital period of the order of 2 seconds that is compatible to the photometrically obtained results. RZ Cas changed its pulsation pattern again. We find at least three pulsation frequencies where one is observed for the first time. All three frequencies show amplitude modulations that are correlated with the position of the star in its orbit. The amplitude amplification around primary minimum is much stronger than in 2001. The modeling of line profiles gives hints to a much more complex and inhomogeneous circumbinary gas density distribution in 2001 compared to 2006. The Rossiter-McLaughlin effect is strongly asymmetric in 2001 and almost normal in 2006.

Conclusions.The findings support the assumption that a rapid mass-transfer episode occurred in RZ Cas in 2000/2001.