Ancient dreams : a spectroscopic study of variable stars in binary systems.
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
This thesis presents the results of the orbital and asteroseismological analysis of three variable stars in binary systems: HD 182640, a system with a candidate γ Doradus primary; HD 3112, a system with a bona fide δ Scuti primary; and HD 147787, a system with a candidate Doradus primary. Approximately 2500 spectra of all three stars were obtained from the HERCULES spectrograph, attached to the 1-metre telescope at the University of Canterbury Mount John Observatory. The raw spectra were reduced to radial velocity line profiles through cross-correlation with synthetic spectra. Orbital analysis of HD 182640 characterised it as a long period (1256 d) binary with an eccentric orbit (e = 0.43). A total of 18 pulsational frequencies, explaining 42.9% of the variation across the line profiles, were identified. These frequencies were all characterised as high degree ( ℓ; > 4) modes. Orbital analysis of HD3112 characterised it as a short period (7 d) binary with an effectively circular orbit (e = 0.01). A total of 17 pulsational frequencies, explaining 46.3% of the variation across the line profiles, were identified. The mode of the primary pulsation frequency ( ƒ1 = 20.2802 d⁻¹) was the only one that was able to be identified. Previously identified ellipsoidal variations may have hindered mode identification efforts. Orbital analysis of HD 147787 characterised it as a moderate period (40 d) binary with an eccentric orbit (e = 0.25). A total of 9 pulsational frequencies, explaining 48.1% of the variation across the line profiles, were identified. The modes of 6 out of the 9 pulsational frequencies, all low-degree ( ℓ; ≤ 3) modes, were able to be identified. The 3 unidentified frequencies are abnormally low for a γ Doradus star. Previously unidentified ellipsoidal variations may have hindered mode identification efforts.