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New observations and models of circumstellar CO line emission of AGB stars in the Herschel SUCCESS programme

AuthorsDanilovich, T.; Teyssier, D.; Justtanont, K.; Olofsson, H.; Cerrigone, L.; Bujarrabal, V.; Alcolea, J.; Cernicharo, José CSIC ORCID; Castro-Carrizo, A.; García-Lario, P.; Marston, A.
KeywordsStars: mass-loss
Circumstellar matter
Stars: evolution
Stars: AGB and post-AGB
Issue Date2-Sep-2015
PublisherEDP Sciences
CitationAstronomy and Astrophysics 581: A60 (2015)
Abstract[Context] Asymptotic giant branch (AGB) stars are in one of the latest evolutionary stages of low to intermediate-mass stars. Their vigorous mass loss has a significant effect on the stellar evolution, and is a significant source of heavy elements and dust grains for the interstellar medium. The mass-loss rate can be well traced by carbon monoxide (CO) line emission.
[Aims] We present new Herschel/HIFI and IRAM 30 m telescope CO line data for a sample of 53 galactic AGB stars. The lines cover a fairly large range of excitation energy from the J = 1 → 0 line to the J = 9 → 8 line, and even the J = 14 → 13 line in a few cases. We perform radiative transfer modelling for 38 of these sources to estimate their mass-loss rates.
[Methods] We used a radiative transfer code based on the Monte Carlo method to model the CO line emission. We assume spherically symmetric circumstellar envelopes that are formed by a constant mass-loss rate through a smoothly accelerating wind.
[Results] We find models that are consistent across a broad range of CO lines for most of the stars in our sample, i.e., a large number of the circumstellar envelopes can be described with a constant mass-loss rate. We also find that an accelerating wind is required to fit, in particular, the higher-J lines and that a velocity law will have a significant effect on the model line intensities. The results cover a wide range of mass-loss rates (~10-8 to 2 × 10-5 M⊙ yr-1) and gas expansion velocities (2 to 21.5 km s-1) , and include M-, S-, and C-type AGB stars. Our results generally agree with those of earlier studies, although we tend to find slightly lower mass-loss rates by about 40%, on average. We also present “bonus” lines detected during our CO observations.
Publisher version (URL)https://doi.org/10.1051/0004-6361/201526705
Identifiersdoi: 10.1051/0004-6361/201526705
e-issn: 1432-0746
issn: 0004-6361
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