New observations and models of circumstellar CO line emission of AGB stars in the Herschel SUCCESS programme
Artikel i vetenskaplig tidskrift, 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: evolution

Circumstellar matter

Stars: mass-loss

Stars: AGB and post-AGB


Taissa Danilovich

Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik

D. Teyssier

European Space Astronomy Centre

Kay Justtanont

Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik

Hans Olofsson

Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik

L. Cerrigone

Netherlands Foundation for Research in Astronomy

V. Bujarrabal

Observatorio Astronomico Nacional

J. Alcolea

Observatorio Astronomico Nacional

J. Cernicharo

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

A. Castro-Carrizo

IRAM Institut de RadioAstronomie Millimetrique

P. Garcia-Lario

European Space Astronomy Centre

A. P. Marston

European Space Astronomy Centre

Astronomy and Astrophysics

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

Vol. 581 A60


Fusion, plasma och rymdfysik