We present mid-infrared ( 2–12 \mu m ) spectra of the microquasar SS 433 obtained with the Infrared Space Observatory ( spectroscopic mode of ISOPHOT and ISOCAM ) .
We compare them to the spectra of four Wolf-Rayet stars : WR 78 , WR 134 , WR 136 , and WR 147 in the same wavelength range .
The mid-infrared spectrum of SS 433 mainly shows H i and He i emission lines and is very similar to the spectrum of WR 147 , a WN8 ( h ) +B0.5V binary .
The 2–12 \mu m continuum emission of SS 433 corresponds to optically thin and partially optically thick free-free emission , from which we calculate a mass loss rate of 2 - 3 \times 10 ^ { -4 } M _ { \odot } \mathrm { yr } ^ { -1 } if the wind is homogeneous and a third of these values if it is clumped .
This is consistent with a strong stellar wind from a WN star .
However , following recent studies concluding that the mass donor star of SS 433 is not a Wolf-Rayet star , we propose that this strong wind out flows from a geometrically thick envelope of material that surrounds the compact object like a stellar atmosphere , imitating the Wolf-Rayet phenomenon .
This wind could also wrap the mass donor star , and at larger distances ( \sim 40 AU ) , it might form a dust envelope from which the thermal emission , detected with ISOPHOT at 25 \mu m and 60 \mu m , would originate .
This wind also probably feeds the material that is ejected in the orbital plane of the binary system and that forms the equatorial outflow detected in radio at distances > 100 AU .