UBC Theses and Dissertations
Nonradial pulsations of rapidly rotating [delta] Scuti stars Kennelly, Edward James
Time series of high resolution CFHT spectra of four δ Scuti stars are examined for consistency with the presence of nonradial pulsations (nrp). Each series exhibits a progression of subfeatures moving from blue to red through the absorption lines. We have reproduced the profile variations using a geometrical model which imposes sectorial modes on the surface of the star. Modeling of the low-degree modes is guided by radial-velocity variations and the known photometric variations. Synthetic spectra generated with the appropriate Teff and log g for each star are used as input for the model. In this way, the entire wavelength region covered by the observations can be reproduced and the effects of blending on the nrp profiles are included explicitly. The extension from a single-line model to one generated over a wide spectral region provides a much more sensitive comparison with the observations. In general, we find that the data can be reproduced by the combination of a high-degree mode (ℓ > 8) and a low-degree mode [ℓ < 2). The intrinsic line widths and υ sinί together set a limit on the resolution of the stellar surface and by including this resolution in our treatment we can estimate the velocity amplitude of the oscillations (~ 5 km/s). We find that low values of k (≤ 0.1) expected for p-mode oscillations are consistent with the observations. A possible relationship between the periods of the high- and low-degree modes is noted, the question of uniqueness is addressed and comparisons are made with models invoking starspots. For at least one of the stars (қ² Boo), it is impossible to fit the observations by a starspot model without assuming unrealistic values of radius or equatorial velocity.
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