# Radial pulsations of red giant branch stars

## TL;DR

This study uses hydrodynamic models to analyze nonlinear pulsations of red giant branch stars, revealing their fundamental mode pulsation characteristics, period changes during core helium flash, and light curve features similar to Mira variables.

## Contribution

It provides new insights into the pulsation behavior and period change rates of red giants during the core helium flash, based on detailed hydrodynamic computations.

## Key findings

- Red giants on the red giant branch are fundamental mode pulsators.
- Pulsation periods range from 254 to 33 days for stars with initial masses 1.1 to 1.9 solar masses.
- Period change rates during the core helium flash are comparable to Mira variable thermal pulses.

## Abstract

We performed hydrodynamic computations of nonlinear stellar pulsations of population I stars at the evolutionary stages of the ascending red giant branch and the following luminosity drop due to the core helium flash. Red giants populating this region of the Hertzsprung--Russel diagram were found to be the fundamental mode pulsators. The pulsation period is the largest at the tip of the red giant branch and for stars with initial masses from 1.1M_\odot to 1.9M_\odot ranges from 254 day to 33 day, respectively. The rate of period change during the core helium flash is comparable with rates of secular period change in Mira type variables during the thermal pulse in the helium shell source. The period change rate is largest (\dot\Pi/\Pi\approx -0.01 yr^{-1}) in stars with initial mass Mzams=1.1M_\odot and decreases to \dot\Pi/\Pi\sim -0.001\ yr^{-1} for stars of the evolutionary sequence Mzams=1.9M_\odot. Theoretical light curves of red giants pulsating with periods Pi > 200 day show the presence of the secondary maximum similar to that observed in many Miras.