Résumé du preprint DAPNIA-02-111

A 2.4 - 12 microns spectrophotometric study of Cygnus X-3 in quiescence with ISO
L. Koch-Miramond, P. Abraham, Y. Fuchs, J.M. Bonnet-Bidaud and Arnaud Claret
We present mid-infrared spectrophotometric results obtained with
ISO on the peculiar X-ray binary Cygnus X-3 in quiescence, at 
 orbital phases 0.83 to 1.04. The 2.4-12 microns continuum radiation observed with ISOPHOT-S can be explained by thermal free-free emission in an expanding wind with, above 6.5 microns, a possible additional black-body component with temperature 
T ~ 250 K and radius R ~ 5000 Rsun at 10 kpc, likely due to 
thermal emission by circumstellar dust. 
The observed brightness and continuum spectrum closely 
match that of the Wolf-Rayet star WR 147, a WN8+BO5 binary system, when rescaled at the same 10 kpc distance as Cygnus X-3. A rough mass loss estimate assuming a WN wind gives 
~ 8.10^-5  Msun/yr. A line at ~ 4.3 micron with a more than 4.3 sigma detection level, and with a dereddened flux of 126 mJy, is interpreted as the expected He I 3p-3s line at 4.295 microns, a prominent line in the WR 147 spectrum.  
These results are consistent with a Wolf-Rayet like companion of 
WN8 type to the compact object in Cyg X-3, a later type than 
suggested by earlier works.


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