Ancient dreams : a spectroscopic study of variable stars in binary systems. (2016)
Type of ContentTheses / Dissertations
Degree NameMaster of Science
PublisherUniversity of Canterbury
AuthorsSekaran, Sanjayshow all
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.