Pulsations of Pre-White Dwarfs with Hydrogen-dominated Atmospheres

TL;DR

This study analyzes nonradial oscillations in pre-white dwarfs with hydrogen atmospheres, revealing how hydrogen burning-shell reactions excite specific g-modes and how hydrogen envelope thickness influences stellar pulsation instability.

Contribution

It provides the first non-adiabatic analysis of pulsations in hydrogen-rich pre-white dwarfs, linking hydrogen envelope properties to observable oscillation modes.

Findings

Hydrogen burning-shell excites low-degree g-modes with periods of 40-200 s.

Hydrogen envelope thickness significantly affects the instability domain.

Observations of g-mode oscillations can constrain hydrogen envelope mass.

Abstract

We carried out a fully non-adiabatic analysis for nonradial oscillations of pre-white dwarfs evolved from the post-Asymptotic Giant Branch (AGB) with hydrogen-dominated envelopes. It is shown that nuclear reactions in the hydrogen burning-shell excite low-degree g-modes in the period range of about 40-200 s for the pre-white dwarf models with Teff=40,000 K - 300,000 K. It is also shown that the amount of hydrogen {has} a significant influence on the instability domain of such pre-white dwarfs in the Hertzsprung-Russel (H-R) diagram. Thus, the thickness of hydrogen-dominated envelopes may be well constrained by observing the presence of the g-mode oscillations.