N. Terasawa et H. Nakamura, IONIZATION STRUCTURE OF CYGNUS-X-3 - IRON ANOMALY IN WOLF-RAYET STARS, Astronomy and astrophysics, 294(2), 1995, pp. 443-452
Ionization structure of the Cygnus X-3 binary system is simulated on t
he basis of the stellar wind model of the luminosity modulation and th
e X-ray spectra observed with GINGA satellite. Emergent spectra are co
mpared with observations to derive constraints on the companion mass a
nd metallicity of the stellar wind. The iron edge absorption energy su
ggests that the companion is fairly massive; M = 7(-2)(+3), M.. Combin
ing the estimated companion mass with the column density of incomplete
ly ionized iron atoms, we find that iron in the stellar wind is somewh
at depleted compared with the cosmic abundance; 0.1 similar to 0.5 tim
es the cosmic abundance. The phase-to-phase spectral variation observe
d with GINGA is well reproduced if the stellar wind gas is enriched wi
th either C, N, or O. These results strongly support the recent infrar
ed observation that the companion of Cygnus X-3 has the feature charac
teristic to N-rich Wolf-Rayet stars. The inferred iron depletion may b
e suggestive to a binary evolution and the nature of Wolf-Rayet stars.
A modest interpretation is that the companion of the Cygnus X-3 is cl
assified to an early WN star (WNE) and the metal deficit is due to the
galactic abundance gradient or the local abundance anomaly.