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

Taissa Danilovich (Institutionen för rymd- och geovetenskap, Radioastronomi och astrofysik) ; D. Teyssier ; Kay Justtanont (Institutionen för rymd- och geovetenskap, Radioastronomi och astrofysik) ; Hans Olofsson (Institutionen för rymd- och geovetenskap, Radioastronomi och astrofysik) ; L. Cerrigone ; V. Bujarrabal ; J. Alcolea ; J. Cernicharo ; A. Castro-Carrizo ; P. García-Lario ; A. Marston
Astronomy and Astrophysics (0004-6361). Vol. 581 (2015),
[Artikel, refereegranskad vetenskaplig]

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.

Nyckelord: Circumstellar matter, Stars: AGB and post-AGB, Stars: evolution, Stars: mass-loss

Denna post skapades 2015-09-17. Senast ändrad 2016-01-25.
CPL Pubid: 222710


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Institutioner (Chalmers)

Institutionen för rymd- och geovetenskap, Radioastronomi och astrofysik (2010-2017)



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