P-Cygni profiles observed in the ultraviolet and visible spectra of Wolf-Rayet stars

• Published in: Monthly notices of the Royal Astronomical Society 1982-04, Vol.198 (4), p.897-920
• Main Author: Willis, Allan J.
• Format: Article
• Language: English
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/198.4.897

High resolution ($\Delta\lambda\sim0.1-0.2$ Å) IUE ultraviolet spectra of ten WR stars have been analysed to investigate P-Cygni profiles in both WN and WC spectra. Measured velocity parameters of these profiles for each star, combined with measurements from visible spectra, are examined for trends with IP and EP of the relevant ionic species and transitions. For each star a well-defined correlation is found between the central-displaced absorption velocity (V0) and EP, demonstrating lower degrees of spectral excitation at higher stellar wind velocities. For the three WN7 stars in the sample, the winds show a mean velocity/EP gradient of $g=(-V_0/\text{EP})$ = − 24.8 ± 5.5 km s−1 eV−1. All other WR subclasses show a similar, shallower, law of g = –12.1 ± 2.3 km s−1 eV−1. The corresponding law for the O4f star ζ Pup is found to be g = −82 km s−1 eV−1. The trend in values of g between these different stellar classes may be linked to the changing structure of their stellar winds expected to occur in the evolutionary scenario which links these stellar classes. In the case of the WC and some WN stars, there is a marked correlation of displaced absorption-edge velocity (Va) with IP for the UV resonance lines. Both V0 and the wind terminal velocities, $V_\infty$ deduced from the UV resonance lines, show an increasing value with excitation subclass in the WN and WC sequences (WC5 and WN5 showing the largest values). In the WC8 star in the sample, violet displaced absorption is observed in the He II λ1215.2 line, but not in H I λ1215.7. Since the wind of this star shows P-Cygni profiles in the low ionisation species of Si II, this result strongly suggests a gross underabundance of H in the WC8 star, and supports the general view of low H/He ratios for the WR class.