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J. Donisan, M. Audard (Columbia University), M. Güdel (Paul Scherrer Institut)
We present multi-wavelength observations of the Algol-type binary RZ Cassiopeiae with XMM-Newton and the VLA. The campaign occurred in August 2003. The secondary eclipse (K3 IV behind A3 V primary) was placed at the center of the 15-hour radio observation, whereas the XMM-Newton monitored a full 1.2 day orbital period. The X-ray light curve shows significant modulation, but does not show evidence of a deep eclipse although the X-ray flux indicates a shallow minimum close to, but after, the time of the optical eclipse. There are, however, indications of a narrow radio eclipse near the time, but before, the time of the optical secondary minimum, apart from more gradual modulation. The spectral slope gets slightly shallower during the radio eclipse. The above suggests different, extended coronal structures emitting in radio and in X-rays, which is reinforced by the different behavior of the light curves during the entire observation. We analyzed the XMM-Newton EPIC and RGS spectra with multi-temperature collisional plasmas. A dominant, hot (20 MK) plasma was found with some plasma at lower temperatures albeit with smaller emission measures. The He-like O VII triplet showed evidence for a high i/f line ratio, probably due to the UV flux of the A3 primary photoexciting electrons in the forbidden state to the intercombination state. However, the low signal-to-noise ratio prevented us from doing a time-dependent analysis as a function of the orbital phase. The high-resolution X-ray spectrum also shows a strong N VII Ly\alpha line but a weak C VI Ly\alpha line. The strong [N/C] enhancement is explained as a signature of CNO-processed material at the surface of the X-ray emitting secondary which fills its Roche lobe and loses material onto the primary.
Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. J.R.D and M.A. acknowledge support from NASA grant NNG04GA42G. M.G. acknowledges support from the Swiss National Science Foundation.
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Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.