Luminosities and masses of single Galactic post-asymptotic giant branch stars with distances from Gaia EDR3: The revelation of an s-process diversity

Devika Kamath*, Hans Van Winckel, Paolo Ventura, Maksym Mohorian, Bruce J. Hrivnak, Flavia Dell'Agli, Amanda Karakas

*Corresponding author for this work

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    Abstract

    Post-asymptotic giant branch (AGB) stars are exquisite probes of AGB nucleosynthesis. However, the previous lack of accurate distances jeopardized comparison with theoretical AGB models. The Gaia Early Data Release 3 (Gaia EDR3) has now allowed for a breakthrough in this research landscape. In this study, we focus on a sample of single Galactic post-AGBs for which chemical abundance studies were completed. We combined photometry with geometric distances to carry out a spectral energy distribution (SED) analysis and derive accurate luminosities. We subsequently determined their positions on the Hertzsprung-Russell (HR) diagram and compared this with theoretical post-AGB evolutionary tracks. While most objects are in the post-AGB phase of evolution, we found a subset of low-luminosity objects that are likely to be in the post-horizontal branch phase of evolution, similar to AGB-manqué objects found in globular clusters. Additionally, we also investigated the observed bimodality in the s-process enrichment of Galactic post-AGB single stars of similar Teff and metallicities. This bimodality was expected to be a direct consequence of luminosity with the s-process rich objects having evolved further on the AGB. However, we find that the two populations, the s-process enriched and non-enriched, have similar luminosities (and hence initial masses), revealing an intriguing chemical diversity. For a given initial mass and metallicity, AGB nucleosynthesis appears inhomogeneous and sensitive to other factors, which could be mass loss, along with convective and non-convective mixing mechanisms. Modeling individual objects in detail will be needed to investigate which parameters and processes dominate the photospheric chemical enrichment in these stars.

    Original languageEnglish
    Article numberL13
    Pages (from-to)1-14
    Number of pages14
    JournalAstrophysical Journal Letters
    Volume927
    Issue number1
    DOIs
    Publication statusPublished - 1 Mar 2022

    Bibliographical note

    Copyright © 2022. The Author(s). Published by the American Astronomical Society. Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.

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