A 2.4-12 μm spectrophotometric study with ISO of Cygnus X-3 in quiescence

L. Koch-Miramond, P. Ábrahám, Y. Fuchs, J. M. Bonnet-Bidaud, A. Claret

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18 Citations (Scopus)


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 T ∼ 250 K and radius R ∼ 5000 R 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 ∼1.2 × 10-4 Myr-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.

Original languageEnglish
Pages (from-to)877-884
Number of pages8
JournalAstronomy and Astrophysics
Issue number3
Publication statusPublished - Dec 2002



  • Infrared: stars
  • Stars: Wolf-Rayet
  • Stars: binaries: close
  • Stars: individual: Cyg X-3
  • Stars: mass-loss

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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