Sub--mm CO Line Observation and Modelling of Circumstellar Shells

Details Sub--mm CO Line Observation and Modelling of Circumstellar Shells Sub--mm CO Line Observation and Modelling of Circumstellar Shells

Nov 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aspc..378..205t&link_type=abstract

Why Galaxies Care About AGB Stars: Their Importance as Actors and Probes. ASP Conference Series, Vol. 378, proceedings of the co

Astronomy and Astrophysics

Astronomy

Scientific paper

We present the results of a multi-transition CO observational program conducted on a sample of AGB and post-AGB star 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. Using a model for the CO emission of an AGB circumstellar envelope, in combination with a standard large-velocity-gradient 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. We find mass-loss rates in the range 1×10-7 to 4×10-4 M_&sun;/yr, and envelope temperatures ranging from 20 K to 1000 K at a radius of 1016 cm. 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.

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