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Astron. Astrophys. 348, 170-174 (1999)

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BeppoSAX broad-band observations of Gamma Cassiopeiae

A. Owens 1, T. Oosterbroek 1, A.N. Parmar 1, R. Schulz 2, J.A. Stüwe 3 and F. Haberl 4

1 Astrophysics Division, Space Science Department of ESA, ESTEC, 2200 AG Noordwijk, The Netherlands
2 Solar System Division, Space Science Department of ESA, ESTEC, 2200 AG Noordwijk, The Netherlands
3 Astronomisches Institut der Ruhr-Universität Bochum, Germany
4 Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse, D-85748 Garching, Germany

Received 11 February 1999 / Accepted 28 April 1999

Abstract

We report broad-band X-ray measurements of the Be star [FORMULA] Cassiopeiae by the BeppoSAX X-ray astronomy satellite. The observations took place on 1998 July, 18-23. The 0.1-200 keV X-ray spectrum is reasonably well fit by an optically thin thermal plasma model of temperature 12.5[FORMULA]0.6 keV with significant residuals around 0.3 keV and 1 keV. The former is interpreted as the variable soft component reported by ROSAT, although there is no evidence for variability at the 5% level. For a blackbody interpretation, the fitted temperature is 100[FORMULA] eV, in agreement with the ROSAT value of 200[FORMULA] 10 eV. However, a MEKAL interpretation gives a significantly lower temperature of (48[FORMULA]11 eV). The fitted abundances are about half solar values, in agreement with previous measurements. At higher energies, the spectrum does not require non-thermal components and the observation of a line at 6.8 keV supports the ASCA interpretation of the source as an accreting white dwarf. Assuming a source distance of 188 pc, the bolometric luminosity in the 2-10 keV band is 6[FORMULA]1032 ergs s-1. Simultaneous optical measurements by the Wendelstein Observatory near Munich, indicate that the source continues to be in a late but rather normal Be phase, with no obvious signs of a transition to the Be-shell phase. The measured magnitudes at B, V and R wavelengths of 2.18[FORMULA]0.06, 2.23[FORMULA]0.02 and 2.36[FORMULA]0.03, respectively, confirm this.

Key words: stars: individual: fl Cas – stars: emission-line, Be – stars: white dwarfs – X-rays: stars

Send offprint requests to: Alan Owens (aowens@astro.estec. esa.nl)

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© European Southern Observatory (ESO) 1999

Online publication: July 16, 1999
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