Ultraviolet P Cygni profiles of the C IV resonance line for O-type stars in the open cluster IC 1805.

Abstract

The ultraviolet C IV resonance lines of seven O-type stars in IC 1805 were observed with the IUE satellite in the low dispersion mode in the 1150-1950 A and 1900-3200 A wavelength ranges. The spectra showed very large and deep P Cygni profiles of the C IV resonance doublet at 1548.20 A and 1550.77 A, and P Cygni characteristics increased with bolometric luminosity. Using this homogeneous stellar sample, the dependence of observational line parameters (equivalent widths of the absorption and emission profiles, terminal velocity) on stellar physical parameters (luminosity, effective temperature, mass, radius) are examined. A Gaussian curve of surface unity and sigma equal to 3A for the IUE instrumental profile at 1550 A in the low dispersion mode was adopted as a first approximation. It was found that maximum values for the terminal velocity are larger than previously observed, while the mass loss index increases linearly with the absolute bolometric magnitude (Mbol); that is, mass loss approximately equals -2.70 Mbol -20.8.