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Paper: Sub–mm CO Line Observation and Modelling of Circumstellar Shells
Volume: 378, Why Galaxies Care About AGB Stars: Their Importance as Actors and Probes
Page: 205
Authors: Teyssier, D.; Bujarrabal, V.; Yoshida, H.; Phillips, T.G.
Abstract: 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 × 10−4M/yr, and envelope temperatures ranging from 20K to 1000K 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. CIT6, 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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