ALMA Observations of CO Isotopologues Towards Six Obscured post-AGB Stars
Low- and intermediate-mass stars evolve through the asymptotic giant branch (AGB), when an efficient mass-loss process removes a significant fraction of their initial mass.
A substantial increase in the mass-loss rate at the end of the AGB is observed for at least some stars for unknown reasons. This creates post-AGB objects that are completely enshrouded in thick dusty envelopes and might be associated with binary interactions.
We observed the J=2−1 line of 13CO, C17O, and C18O with the Atacama Large Millimeter / submillimeter Array (ALMA) towards six obscured post-AGB stars (four C-rich and two O-rich sources) to constrain the properties of their circumstellar envelopes, recent mass-loss histories, and initial mass of the central stars.
Based on the inferred 17O/18O isotopic ratios, we find all stars to have relatively low initial masses (<2 M⊙) contrary to suggestions in the literature of higher masses for some sources. We infer a mass for HD~187885 ∼1.15 M⊙, which is relatively low for a carbon star.
For all but one source (GLMP~950), we observe kinematic components with velocities ≳30~km~s−1, which are faster than typical AGB wind expansion velocities. For most sources, these higher-velocity outflows display point-symmetric morphologies. The case of Hen~3-1475 is particularly spectacular, with the high-velocity molecular outflow interleaved with the high-velocity outflow of ionised gas observed at optical wavelengths.
Based on the size of the emission regions of the slow components of the outflows, we derive typical kinematic ages associated with the C18O~J=2−1 emission ≲1500~years and obtain relatively high associated mass-loss rates (≳10−4 M⊙ yr−1). The sources with known spectral types are found to have evolved faster than expected based on stellar evolutionary models.
T. Khouri, D. Tafoya, W. H. T. Vlemmings, H. Olofsson, C. Sánchez Contreras, J. Alcolea, J. F. Gómez, L. Velilla-Prieto, R. Sahai, M. Santander-García, V. Bujarrabal, A. Karakas, M. Saberi, I. Gallardo Cava, H. Imai, A. F. Pérez-Sánchez
Comments: Accepted for publication in Astronomy & Astrophysics
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2501.04492 [astro-ph.SR] (or arXiv:2501.04492v1 [astro-ph.SR] for this version)
https://doi.org/10.48550/arXiv.2501.04492
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From: Theo Khouri
[v1] Wed, 8 Jan 2025 13:25:21 UTC (1,041 KB)
https://arxiv.org/abs/2501.04492
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