Volume 396, Number 3, December IV 2002
|Page(s)||877 - 884|
|Section||Interstellar and circumstellar matter|
|Published online||05 December 2002|
A 2.4–12 μm spectrophotometric study with ISO of Cygnus X-3 in quiescence*
DAPNIA/Service d'Astrophysique, CEA-Saclay, 91191 Gif-sur-Yvette Cedex, France
2 Konkoly Observatory, PO Box 67, 1525 Budapest, Hungary
3 Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
4 Université Paris VII, France
Corresponding author: L. Koch-Miramond, email@example.com
Accepted: 28 June 2002
We present mid-infrared spectrophotometric results obtained with the ISO on the peculiar X-ray binary Cygnus X-3 in quiescence, at orbital phases 0.83 to 1.04. The 2.4–12 μm continuum radiation observed with ISOPHOT-S can be explained by thermal free-free emission in an expanding wind with, above 6.5 μm, a possible additional black-body component with temperature K and radius 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+B0.5 binary system, when rescaled at the same 10 kpc distance as Cygnus X-3. A rough mass loss estimate assuming a WN wind gives ~ yr-1. A line at ~4.3 μm with a more than 4.3 σ detection level, and with a dereddened flux of 126 mJy, is interpreted as the expected He I 3p–3s line at 4.295 μm, a prominent line in the WR 147 spectrum. These results are consistent with a Wolf-Rayet-like companion to the compact object in Cyg X-3 of WN8 type, a later type than suggested by earlier works.
Key words: stars: binaries: close / stars: individual: Cyg X-3 / stars: Wolf-Rayet / stars: mass-loss / infrared: stars
© ESO, 2002
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