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Abstract: gamma Cassiopeiae gCas is a B0.5e star with peculiar X-ray emissionproperties and yet the prototype of its own small class. In this paper weexamine the X-ray spectra for a 2004 XMM-Newton observation and a previouslypublished 2001 Chandra observation. In both cases the spectra can be modeledwith 3 or 4 thermal components, which appear be discrete in temperature andspatially distinct. The dominant component, having kT ~ 12 keV contributes most~80-90% of the flux. The secondary components have temperatures in the rangeof 2-3 keV to 0.1 keV; these values can shift in time. Importantly, we findthat the strong absorption of soft X-rays in 2001 is absent in 2004, meaningthat an absorbing column in front of the source has moved off the star or hasbeen removed. Other differences include a reduced Fe abundance from the ionizedlines of the FeKalpha complex even more subsolar than the 2001 observation, adecrease of the Fe K and possibly of the Si K fluorescence features, and fromthe NVII and NeX H-alpha lines, a possible overabundance of N and Ne. Also, wenote common characteristics in both spectra that seem to set gCas apart fromHD110342, another member of this subclass studied in detail. In this sensethese stars have different -personalities.- For example, for gCas rapid X-rayflaring and slower changes in the light curve are only seldomly accompanied byvariations in hardness, and the hot X-ray component remains nearly constant intemperature. Moreover, the light curve shows recurrent -lulls- in flux,suggesting that a relaxation cycle is operates as part of the unknown X-raygeneration process.

Author: Raimundo Lopes de Oliveira 1, Myron A. Smith 2, Christian Motch 3; 1-IAG-USP, Brazil; 2- Catholic University of America, USA; 3-



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