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High Precision Optical Interferometry and Application to Be Stars

Christopher Tycner

Doctor of Philosophy 2004
Graduate Department of Astronomy and Astrophysics, University of Toronto

A new technique for calibrating optical long-baseline interferometric observations is developed where both the calibration corrections and the source characteristics are obtained from the observations of a program star. This calibration technique can only be applied to certain classes of objects, such as emission line sources or binary systems, where the parameters describing the characteristics of the source have different functional dependence than the calibration parameters. To demonstrate its effectiveness, the technique is applied to observations of four different Be stars obtained with the Navy Prototype Optical Interferometer. The interferometric observations utilize measurements obtained simultaneously in many spectral channels covering a wide spectral range, where only two channels contain a strong signal due to the circumstellar envelope in the Hα emission line. The calibrated observations in Hα allow modeling of the circumstellar envelopes of all four stars with circularly symmetric and elliptical Gaussian models. The best-fit model parameters are then combined with similar results for other Be stars, already published in the literature, to study the relationship between the Hα emission and the physical extent of the Hα-emitting circumstellar region. For the first time, a clear dependence of the net Hα emission on the extent of the circumstellar region is demonstrated. These results are consistent with an optically thick line emission that is directly proportional to the effective area of the emitting disk. Within the small sample of stars considered in this analysis, no clear dependence on the spectral type of stellar rotation is established, although the results do suggest that hotter stars might have more extended circumstellar regions.

Reproduced with permission. library@astro.utoronto.ca
October 18 2004