Mathematics – Logic
Scientific paper
Nov 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998phdt.........5k&link_type=abstract
Thesis (PHD). GEORGIA STATE UNIVERSITY , Source DAI-B 59/05, p. 2246, Nov 1998, 187 pages.
Mathematics
Logic
11
Scientific paper
The so-called 'γ Doradus stars' are revealing the first evidence of oscillation in gravitational g-modes (pulsations that are excellent probes of the stellar interior structure) in the lower part of the classical Cepheid instability strip. The extraction of this asteroseismological information, and therefore the understanding of the critical stellar parameters and basic stellar physics, requires a reliable mode identification possible only through multi-site campaigns that involve both high- precision photometry and spectroscopy. For six of the newly-discovered γ Doradus-type variable stars, I present multi-site, two-color, differential photometry and for four of the targets. I also present simultaneous high signal-to-noise spectroscopy of the Fe II λ4508.289 and Ti II λ4501.278 lines. This data was obtained using the Vanderbilt University/Tennessee; State University 0.4-m Automatic Photoelectric Telescope, the Sierra Nevada Observatory 0.9-m telescope and multi-channel photometer (Spain), and the Kitt Peak National Observatory 0.9-m coude feed telescope. For representative nights with sufficient coverage, the rapid time evolution of the spectroscopic profiles is displayed as a gray-scale image which shows the intensity deviations from the average profile as a function of both time and wavelength, clearly showing line profile variations in most cases. I calculate power spectra for both the photometric and the spectroscopic time series in order to search for periodic variability; and I apply the CLEAN algorithm to these periodograms to help remove aliases due to gaps in my data sampling. Determination of the pulsation 'quantum numbers' l and m for each periodic signal in each of the four target objects having both photometric and spectroscopic data are calculated using the method of moments. Based on this analysis, the conclusion that all six of the target objects are pulsating in non-radial, low-degree, gravity modes is reached. As a 'bonus' result of this analysis, HD 62454 was discovered to be a double-lined spectroscopic binary.
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