Issue |
A&A
Volume 450, Number 1, April IV 2006
|
|
---|---|---|
Page(s) | 167 - 179 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20053759 | |
Published online | 03 April 2006 |
CO line emission from circumstellar envelopes
1
Departamento de Astrofísica Molecular e Infrarroja, IEM, CSIC, 28006 Madrid, Spain
2
Space Research Organization Netherlands, P.O. Box 800, 9700 AV Groningen, The Netherlands e-mail: teyssier@sron.rug.nl
3
Observatorio Astronómico Nacional, Apartado 1143, 28800 Alcalá de Henares, Spain e-mail: v.bujarrabal@oan.es
4
Caltech Submillimeter Observatory, 111 Nowelo Street, Hilo, HI 96720, USA e-mail: hiro@submm.caltech.edu
5
California Institute of Technology, Pasadena, CA 91125, USA e-mail: phillips@submm.caltech.edu
Received:
4
July
2005
Accepted:
30
December
2005
Aims.We present the results of a multi-transition CO observational program conducted on a sample of
AGB and post-AGB stars envelopes. We have collected maps and single pointing
observations of these envelopes in 5 rotational transitions ranging
from J = 1–0 to J = 6–5, including in particular new observations
of the CO line at 691 GHz at the CSO. The use of such a set of mm
and submm CO line on stellar envelopes is rare and limited to the
work of some authors on IRC+10216.Methods.Using a model for the CO emission of an AGB circumstellar
envelope, in combination with a standard LVG approach, we have
conducted a systematic modelling analysis using the whole set of CO data collected for a sample
of 12 sources. We simultaneously fit all
five transitions, taking into account the spatial information provided
by the maps.Results.We find mass-loss rates in the range
1 10-7 to 4
10
/yr, and
envelope temperatures ranging from 20 K to 1000 K at a radius of
1016 cm. There seem to be a general anti-correlation between
mass loss rates and temperature, the high mass loss rate AGBs
having low temperatures, and vice versa. We show that most AGB data
can be fitted using a constant mass loss rate, at least within the
calibration uncertainties associated with the data collected at
different frequencies. For some cases though (e.g. CIT 6, R Hya,
χ Cyg), a change in the mass loss rate history needs to be
invoked to reconcile data at low- and high-J, a scenario already
mentioned by several authors to explain observations of WX Psc.
© ESO, 2006
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