Speaker
Description
Low- and intermediate-mass stars experience a series of thermal pulses after reaching the asymptotic giant branch. Currently, three stars are suspected to be undergoing a thermal pulse: the variable stars T UMi, R Hya, and RU Vul. While detailed analyses have already been conducted for the first two, no such modeling has yet been performed for RU Vulpeculae. Since the both the amplitude and period of RU Vul have significantly decreased over the last decades, we started long-term multicolor observations from Piszkéstető Observatory on a weekly basis in January 2022. I extracted five years of standardized photometry of the star and performed a detailed frequency analysis of the pulsation. Based on this, I successfully confirmed our hypothesis that the star has recently transitioned from single-mode into double-mode pulsation. This is fully analogous with the behavior observed in T UMi, which recently began a thermal pulse.
Subsequently, I examined the long-term evolution of RU Vul's pulsation period. By utilizing archival observational data, I mapped the evolution of the pulsation period over nearly 130 years, determined the exact time of the onset of the thermal pulse, the rate of period change since then, and the time of first excitation of the first overtone. This work lays the groundwork for modeling the thermal pulse of the star via combined evolutionary and seismic models, which will allow for the determination of several physical parameters, including the mass of RU Vul.