Theoretical models for the Late Thermal Pulse in post-AGB stars: the case of DY Cen

TL;DR

This paper develops theoretical models for the late thermal pulse phenomena in post-AGB stars, especially applied to DY Cen, and finds that current models cannot fully explain its observed properties.

Contribution

The study constructs an extensive grid of born-again star models including VLTP and LTP scenarios, analyzing parameter dependencies and applying them to DY Cen.

Findings

Models do not match DY Cen's surface chemistry

DY Cen unlikely to be a born-again star

Parameter space analysis enhances understanding of post-AGB evolution

Abstract

We present theoretical predictions of the born-again scenario for post-asymptotic giant-branch stars. An extensive model grid for born-again objects has been constructed, particularly including models for the Very Late Thermal Pulse with and without convective overshooting, and also including models for the Late Thermal Pulse. We constructed a large parameter space to analyze the dependencies of the born-again model on core mass, hydrogen-envelope mass, and overshoot parameters, and we analyzed how changes in these parameters affect the models' evolution. We applied our grid of models to interpret observations of DY\,Cen, a star exhibiting characteristics similar to confirmed born-again stars. We compared DY\,Cen with models from multiple aspects, including heating rate, evolutionary tracks, and surface abundances. Ultimately, we concluded that none of our born-again models could match all of the observed properties of DY\,Cen, especially its surface chemistry; DY\,Cen is therefore an unlikely born-again star.