Variation of emission features in γ2 Velorum

The bright southern star (1.82 visual magnitude), γ2 Velorum, is a spectroscopic binary consisting of a Wolf-Rayet star and an O-type star. The emission lines in its spectrum show variations on the order of minutes as observed by a number of investigators. Photoelectric photometry of γ2 Velorum was made with the use of the automated 3-inch South Pole Optical Telescope during the austral winters of 1986, 1987 and 1988. Detailed reduction and analysis of the observational data are being carried out and will be presented elsewhere. The result of a sample 5-hour run of the HeII emission line, which is a subset of a 16-hour data set, is given here. The ratio of the brightness measurement of the line feature to that of the continuum is calculated; and power spectrum is computed. The relatively strong peak, which occurs at 19.0 per day, corresponds to a period of 1.26 hours. A sine curve was also fitted to the normal points of these data, computed at 0.004-day intervals, with the use of the method of least squares. This model yields a period of 1.28 hours. The strong agreement between these two methods leads to the belief that this in a real variation in γ2 Velorum. This new discovery will aid in the study of the nature of the extended atmosphere of the Wolf-Rayet star system