I present orbital-phase resolved K-band spectra of Cyg X-3. These show emission lines that shift in wavelength during the orbit, with maximum blueshift coinciding with X-ray and infrared minimum, and maximum redshift half an orbit later. I propose that this is due to the fact that during the observations the wind of the helium star was almost completely ionized by the X-ray source, except for the part shadowed by the helium star. With this hypothesis one can also understand the orbital modulation of the infrared continuum flux, as well as the fact that it is modulated in phase with the X-ray flux. I present numerical calculations on a simple model for the source, and show that for reasonable parameters it is possible to reproduce the observed spectroscopic and photometric orbital modulation.
Astronomy and Astrophysics
- Pub Date:
- September 1993
- Binaries: close - Stars: individual: Cygnus X-3 - Stars: Wolf-Rayet - X-rays: stars