New observations and models of circumstellar CO line emission of AGB stars in the Herschel SUCCESS programme
Journal article, 2015

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.

Stars: AGB and post-AGB

Stars: evolution

Circumstellar matter

Stars: mass-loss

Author

Taissa Danilovich

Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics

D. Teyssier

European Space Astronomy Centre (ESAC)

Kay Justtanont

Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics

Hans Olofsson

Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics

L. Cerrigone

Netherlands Institute for Radio Astronomy (ASTRON)

V. Bujarrabal

Spanish National Observatory (OAN)

J. Alcolea

Spanish National Observatory (OAN)

J. Cernicharo

CSIC - Instituto de Ciencia de Materiales de Madrid (ICMM)

A. Castro-Carrizo

Institut de RadioAstronomie Millimetrique (IRAM)

P. Garcia-Lario

European Space Astronomy Centre (ESAC)

A. P. Marston

European Space Astronomy Centre (ESAC)

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 581 A60

Subject Categories

Fusion, Plasma and Space Physics

DOI

10.1051/0004-6361/201526705

More information

Latest update

9/6/2018 1