Understanding dust production and mass loss on the AGB phase using post-AGB stars in the Magellanic Clouds

TL;DR

This study investigates dust production and mass loss during the AGB phase by analyzing post-AGB stars in the Magellanic Clouds, combining observational data with stellar evolution models to understand surface chemistry and dust formation processes.

Contribution

It provides new insights into the chemical and dust evolution of post-AGB stars, linking observed properties with stellar progenitors and dust mineralogy.

Findings

8 out of 13 stars are carbon-rich from 1-2.5 Msun progenitors.

5 stars are silicate-rich from less than 1 Msun progenitors.

Dust observed was released after star contraction and temperature increase.

Abstract

Aims: We aim to understand the variation of the surface chemistry that occurs during the AGB phase by analysing results from observations of single post-AGB stars in the Magellanic Clouds. We also aim at reconstruct dust formation processes, that are active in the circumstellar envelope of AGB stars. Methods: We study likely single post-AGB sources in the Magellanic Clouds that exhibit a double-peaked (shell-type) spectral energy distribution (SED). We interpret their SED by comparing with results from radiative transfer calculations, to derive the luminosity and the dust content of the individual sources. Additionally, we compare the observationally derived stellar parameters and the photospheric chemical abundances of the target sample with results from stellar evolution modelling of AGB and post-AGB stars. This allows for the characterization of the individual sources in terms of initial mass and formation epoch of the progenitors. Results: We find that amongst our target sample of 13 likely single post-AGB stars with shell-type SED, 8 objects are carbon stars descending from ~1-2.5 Msun progenitors. 5 of the 13 objects are of lower mass, descending from M<1 Msun stars. Based on the dust mineralogy, we find that these 5 stars are surrounded by silicate dust, and thus failed to become carbon stars. The dust optical depth and the luminosity of the stars are correlated, owing to the faster evolutionary time-scale brighter stars, which makes the dusty layer to be closer to the central object. From our detailed analysis of the SEDs, we deduce that the dust currently observed around post-AGB stars was released after the onset of the central star contraction and an increase in the effective temperature to ~3500-4000 K.