Stellar Evolution in Real Time. II. R Hydrae and an Open-Source Grid of >3000 Seismic TP-AGB Models Computed with MESA

Abstract

We present a comprehensive characterization of the evolved thermally pulsing asymptotic giant branch (TP-AGB) star R Hydrae (R Hya), building on the techniques applied in Stellar Evolution in Real Time I (Molnár et al.) to T Ursae Minoris. We compute over 3000 theoretical TP-AGB pulse spectra using MESA and the corresponding oscillation spectra with GYRE. We combine these with classical observational constraints and nearly 400 years of measurements of R Hya’s period evolution to fit R Hya’s evolutionary and asteroseismic features. Two hypotheses for the mode driving R Hya’s period are considered. Solutions that identify this as the fundamental mode (FM) as well as the first overtone are consistent with observations. Using a variety of statistical tests, we find that R Hya is most likely driven by the FM and currently occupies the “power-down” phase of an intermediate pulse (TP ∼ 9–16). We predict that its pulsation period will continue to shorten for millennia. Supported by calculations from the Monash stellar evolution code, we find that R Hya has most likely undergone third dredge-up in its most recent pulse. The MESA + GYRE model grid used in this analysis includes exact solutions to the linear, adiabatic equations of stellar oscillation for the first 10 radial-order pressure modes for every time step in every evolutionary track. The grid is fully open source and packaged with a data visualization application. This is the first publicly available grid of TP-AGB models with seismology produced with MESA.