THE EXTENT OF VARIABILITY IN THE STELLAR WIND OF THE O-7.5 GIANT XI-PERSEI

Using high-time-resolution ultraviolet spectroscopy, we present eviden ce that variability in the stellar wind of the O 7.5 III(n)((f)) star xi Per takes place essentially over the whole velocity range over whic h the wind is observable in absorption: from approximately -100 km s-1 in the Si IV line up to -2750 km s-1 in N V and C IV, about 400 km s- 1 beyond the terminal velocity of the stellar wind. The variations in the absorption part of the P Cygni profile include the discrete absorp tion components (DACs), which represent the strongest manifestations o f the wind variability. In contrast, the emission part of the profile is steady. The blue steep edge in the saturated P Cygni lines varies i n concert with the DACs. The changes in the subordinate N IV line at 1 718 angstrom at low velocity (approximately -250 to approximately -800 km s-1) are found to vary in concert with the appearance of DACs in t he Si iv lines. This implies that DACs are formed in a region relative ly close to the surface. An evaluation of the statistical significance of variations in IUE spectra is presented.