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We present mid-infrared spectrophotometric results obtained with the ISO onthe peculiar X-ray binary Cygnus X-3 in quiescence, at orbital phases 0.83 to1.04. The 2.4-12 microns continuum radiation observed with ISOPHOT-S can beexplained by thermal free-free emission in an expanding wind with, above 6.5microns, a possible additional black-body component with temperature T ~ 250 Kand radius R ~ 5000 solar radii at 10 kpc, likely due to thermal emission bycircumstellar dust. The observed brightness and continuum spectrum closelymatch that of the Wolf-Rayet star WR 147, a WN8+B0.5 binary system, whenrescaled at the same 10 kpc distance as Cygnus X-3. A rough mass loss estimateassuming a WN wind gives ~ 1.2 10^{-4} M(sun)/yr. A line at ~ 4.3 microns witha 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 prominentline in the WR 147 spectrum. These results are consistent with aWolf-Rayet-like companion to the compact object in Cygnus X-3 of WN8 type, alater type than suggested by earlier works.Comment: 8 pages, 10 figures ; Accepted in A&

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