Ionization structure of Cygnus X-3: iron anomaly in Wolf-Rayet stars?

Ionization structure of the Cygnus X-3 binary system is simulated on the basis of the stellar wind model of the luminosity modulation and the X-ray spectra observed with GINGA satellite. Emergent spectra are compared with observations to derive constraints on the companion mass and metalicity of the stellar wind. The iron edge absorption energy suggests that the companion is fairy massive; M = 7(+3-2)M_sun. Combining the estimated companion mass with the column density of incompletely ionized iron atoms, we find that iron in the stellar wind in somewhat depleted compared with the cosmic abundance; 0.1 #propor to# 0.5 times the cosmic abundance. The phase-to-phase spectral variation observed with GINGA is well reproduced if the stellar wind gas is enriched with any one of C, N, and O. These results strongly support the recent infrared observation that the companion of Cygnus X-3 has the feature characteristic to N-rich Wolf-Rayet stars. The inferred iron depletion may be suggestive to a binary evolution and the nature of Wolf-Rayet stars. A modest interpretation of the metal deficit is that the companion of the Cygnus X-3 is classified to early WN stars (WNE). (orig.)Available from TIB Hannover: RN 9303(284) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman