Rapid Variability in the Spectral Lines of Be Stars

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Stars have wide ranges of masses, ages, rotation rates, and other physical properties. For example, Be stars are relatively young, rapidly rotating stars of type B, with surface temperatures above 10,000 K and characteristic emission features (hence, the "e" in Be) in their hydrogen Balmer lines. During the last few years, photometric and spectroscopic observations have revealed variations in the colors and in the absorption lines of Be stars that move from the blue to the red, on time scales of 0.2 to 2 days, and that so far have defied unique physical explanation. Vogt and Penrod have interpreted these variations as being due to nonradial pulsations (NRPs) in the stars' photospheres. The PI will test the NRP model with a time series analysis of the stars' absorption line variations. Furthermore, he will compare variations in the stars' photospheres, circumstellar disks, and high velocity winds to determine whether the proposed NRPs are responsible for the mass loss observed from these and, possibly, other rapidly rotating stars.