THE IONIZATION STRUCTURE OF CYGNUS-X-3 - A MASSIVE IRON-DEPLETED COMPANION

We investigate the ionization structure of the stellar wind of the Cyg nus X-3 binary, exposed to luminous X-ray emission from the compact ob ject. Comparing the simulated X-ray spectra with the observed ones, we find that the companion star is fairly massive (5 less than or simila r to M less than or similar to 10 M.), and that iron in the stellar wi nd is somewhat depleted, to 0.1-0.5 times the cosmic abundance. The ph ase-to-phase change of the X-ray spectrum implies that the wind gas is enriched in any one of C, N or O. These results strongly support the recent infrared observation.