A search for UV-line profile variability in five 0-stars.

Abstract

Five O-stars have been monitored with IUE in the far-UV, at high resolution, to study resonance line profile variability. The O-type stars Zeta Pup, 9Sgr, HD 175754, Lambda Ori A, and HD 105056 have strong stellar winds. Their resonance line profiles of N V, Si IV, and C IV ions, observed at different epochs since May 1978, have been compared in the displaced absorption components. Noticeable evidence of profile changes is detected in the spectra of Lambda Ori A, Zeta Pup, and HD 175754. From the profile shapes and associated variability it is inferred that two different mechanisms could be producing the observed ionization stages: a thermal mechanism in a hot post-coronal region, at an electron temperature of 2 x 10 to the 5th K, and an Auger mechanism of ionization of cool high velocity gas by X rays coming from inner coronal regions.