Gravity modes present in gamma Doradus stars probe the deep stellar interiors and are thus of particular interest in asteroseismology. Mode identification will improve the knowledge of these stars considerably and allow an understanding of the issues with current pulsational models. The methods used in this thesis are also applied to a low degree pressure mode pulsator as a check for their validity. A frequency analysis followed by a mode identification were done based on the high resolution spectroscopic data of one β Cephei star, PT Puppis, and two γ Doradus stars, HD 189631 and AC Lepus. Extensive spectroscopic data sets are obtained by three instruments: HARPS, FEROS and HERCULES. We obtained 161 spectra for PT Puppis, 422 spectra for HD 189631 and 248 spectra for AC Lepus. The pulsational frequencies were determined by four methods: analysis of the variations in equivalent width, radial velocity, asymmetry of the line profile and by using the pixel-by-pixel frequency analysis. The mode identification was done using the recently developed Fourier Parameter Fit method. Without achieving the same degree of confidence for all results, we report the identification of two pulsational modes in PT Puppis: (l = 0 ; m = 0) at f₁ = 6.07 d⁻¹ and (2 ; 0) or (1 ; +1) at f₂ = 5.99 d⁻¹, four modes in HD 189631: (1 ; +1) at f₁ = 1.67 d⁻¹, (3 ; -2) at f₂ = 1.42 d⁻¹, (2 ; -2) at f₃ = 0.07 d⁻¹ and (4 ; +1) at f₄ = 1.82 d⁻¹ and two modes in AC Lepus: (2 ; -1) at f₁ = 0.75 d⁻¹ and (3 ; -3) at f₂ = 1.09 d⁻¹. This study provides the first pulsational analysis based on spectroscopy of PT Puppis, HD 189631 and AC Lepus. We discuss the performance of current methods of analysis, outline the difficulties presented by γ Doradus stars, and compare our results with other published pulsational mode identifications.

This thesis has analysed spectroscopic data for three stars in detail, the β Cephei star V2052 Ophiuchus, the γ Doradus star QW Puppis and the γ Doradus candidate star HD139095. Twelve other candidate γ Doradus stars have had their Vrotsin i, binary status and, where possible, the presence of line profile variation determined. A new technique utilising scaled delta functions has been developed to allow the extraction of a single, high S/N line profile from a high resolution and large wavelength range spectrum. This procedure has performed well in the γ Doradus stars examined. The application of the new mode identification technique, the Fourier Parameter Fit method, to the three stars examined in detail has been very successful. For each of the three stars constraints have been placed on the degree (l) and the azimuthal order (m) of the non-radial pulsation modes detected.

The success of asteroseismology lies in the correct identification of the normal modes of oscillation. The Whole Earth Telescope (WET) identified the normal modes of a helium white dwarf pulsator, GD358, by analyzing the period distribution of the pulsation modes. Another way to identify modes is by comparing pulsation amplitudes in the UV to the optical. To cross-calibrate the two mode identification methods, we observed GD358 in August, 1996 with the Hubble Space Telescope (HST) to obtain the UV data while observing nearly simultaneously from the ground. During our observations, GD358 went through a very drastic amplitude modulation in a time scale of hours. These short time scale amplitude changes made the direct UV to optical amplitude determinations difficult. We successfully eliminate the possibility that the 423s mode, the dominant mode at the time of these observations, is an l=3 or 4 g-mode pulsation, but we cannot unambiguously decide if it is an l=1 or 2. Theoretical calculations indicate that the massive pulsating DA white dwarf BPM 37093 has a crystallized interior (Winget et al. 1997; Kanaan 1996; Montgomery 1998). Crystallization was predicted theoretically 40 years ago (Kirshnitz 1960; Abrisokov 1961; Salpeter 1961) although uncertainties in the nature and extent of crystallization, as well as its associated effects, are the largest sources of uncertainty in calculating the ages of the coolest white dwarf stars- important chronometers of the galactic disk. The WET observed BPM 37093 in April 1998 and again in April 1999, simultaneously with the HST, in hopes of using both the period distribution and the amplitude comparison method to identify the l value of the modes and measure the first crystallized mass-fraction of a stellar interior. Here we also rule out the possibility of the observed modes being l=3 and higher and demonstrate that not all the observed modes are l-1. If all the observed modes are l-2, then we conclude that the crystallization mass fraction is between 0-80%, depending mainly on the surface H layer. In the end, we evaluate the amplitude comparison method and address advantages and problems using this method compared to other mode identification methods. / text

We present the modes identified for frequencies found in spectroscopic observations of the Doradus stars HD 189631, QW Puppis, and IR Draconis. A cross-correlation tech- nique was used to create mean line profiles for HD 189631. Four frequencies and modes were identified for this star: 1.6774±0.0002 d⁻¹, 1.4174±0.0002 d⁻¹, 0.0714±0.0002 d⁻¹, and 1.8228 ± 0.0002 d⁻¹ which were identified with the modes (l,m) = (1, +1), (1, +1), (2,−2), and (1, +1) respectively. A least-squares deconvolution method was implemented for line profile generation in the study of QW Puppis and IR Draconis. Three frequen- cies were identified for QW Puppis: 0.055972 ± 0.000004 d⁻¹, 0.064846 ± 0.000004, and 5.219398±0.000002 d⁻¹. These frequencies were identified with the modes (l,m) = (1,−1), (4,−1), (4, +1). Two frequencies were identified in spectra of the rapidly rotating star IR Draconis: 0.00515 ± 0.00003 d⁻¹ and 2.35538 ± 0.00004 d⁻¹; which were identified with (l,m) = (1,−1), and (1, +1) modes respectively. These mode identifications will assist in modelling the structure and interior conditions of these main sequence, non-radially pulsating stars.

Three γ Doradus-type stars are analysed: HD139095, HD153580, and HD197541. Long-term observation campaigns have been conducted on each star, with over 300 spectra of each star being gathered for analysis using the HERCULES spectrograph at Mount John University Observatory. For each star, cross-correlation techniques were used to obtain representative line profiles for each spectrum. The analysis of these line profiles has resulted in frequency and pulsation mode identifications for these three stars. Abundance analysis has also been performed on HD139095 and HD197541, and their fundamental parameters are confirmed as being consistent with the γ Doradus class of stars. HD153580 and HD197541, previously only candidates for the class, can now be classified as bona fide γ Doradus type stars. The frequencies and modes identified in this thesis will be very useful in constraining future theoretical models, allowing us to better understand and model the interiors of γ Doradus stars.

This thesis has analysed spectroscopic data for three stars in detail, the β Cephei star V2052 Ophiuchus, the γ Doradus star QW Puppis and the γ Doradus candidate star HD139095. Twelve other candidate γ Doradus stars have had their Vrotsin i, binary status and, where possible, the presence of line profile variation determined. A new technique utilising scaled delta functions has been developed to allow the extraction of a single, high S/N line profile from a high resolution and large wavelength range spectrum. This procedure has performed well in the γ Doradus stars examined. The application of the new mode identification technique, the Fourier Parameter Fit method, to the three stars examined in detail has been very successful. For each of the three stars constraints have been placed on the degree (l) and the azimuthal order (m) of the non-radial pulsation modes detected.