Photometry and spectroscopy of RV Tauri stars. (2020)
Type of ContentTheses / Dissertations
Degree NameMaster of Science
PublisherUniversity of Canterbury
AuthorsBhardwaj, Kunalshow all
RV Tauri stars are recognized as radially pulsating, post-Asymptotic Giant Branch stars, in the high-luminosity end of type-II Cepheids. They show char- acteristic light modulations and spectral line variations which are generally linked with intrinsic radial pulsations and resulting shock waves. This thesis investigates stellar pulsations in a sample of RV Tauri stars using a mix of analytical methods. In particular, it examines the short-term and long-term variability by searching for periodicities in the photometric and spectroscopic data for a number of selected southern hemisphere RV Tauri stars. These data are used to explore how the vari- ability and other observed stellar properties, fit within the current theories which explain RV Tauri behaviour as being due to stellar pulsation, binarity, and interac- tion with its local environment, including circumbinary dust.
We use extensive visual photometric data from the AAVSO International Database for analysing the long-term and short-term variations and recent BV data for analysing the short-term pulsations. AAVSO’s VPhot was used to perform differen- tial photometry for the BV data and Period04 was used for Fourier analysis and least-squares fitting in a pre-whitening manner to find periodicites in both visual and BV data.
Both short-term pulsational and most of the long-term periods of all the stars studied were found to be in reasonable agreement with the published values. The amplitude of the long-term periods was substantial in variation. Complex peak structures are seen in periodograms possibly owing to period changes over time and/or “flips” seen in the deep-shallow light curve alternation with time. These variations in both short and long-term periods (and also amplitude) over time is confirmed in wavelet analysis of U Mon and IW Car.
Nearly 100 spectra of U Mon were acquired over 5 months to cover ∼1.5 cycles of its 92-day pulsation period. Effects of two pulsation-related shock-waves per pulsation cycle were seen on specific spectral line profiles, consistent with previous studies. The new pulsational radial velocity curves measured by Gaussian profile fitting to the Fe I line at 6200.313 ˚A show well-defined consistency with the published pulsational radial velocity curve. The results in this thesis add depth and scope to the leading RV Tauri model which explains the light and spectral variations in RVb stars through a combination of binarity, intrinsic stellar pulsations, interaction and obscuration mechanisms involving binaries and circumstellar/circumbinary disk depending on the observer’s perspective.