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Astron. Astrophys. 359, 1162-1168 (2000)

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ISO-SWS Observations of CO2 and H2O in R Cassiopeiae *

A.J. Markwick and T.J. Millar

Department of Physics, UMIST, P.O. Box 88, Manchester M60 1QD, UK

Received 21 March 2000 / Accepted 22 May 2000


We present ISO-SWS spectra of the O-rich Mira variable R Cas, showing CO2 in absorption and emission, and H2O in absorption. The CO2 absorption feature is the [FORMULA] ro-vibrational band at [FORMULA]. The emission features are the [FORMULA] and [FORMULA] ro-vibrational transitions at 13.87 and [FORMULA] respectively. The water absorption spectrum shows the [FORMULA] and [FORMULA] ro-vibrational bands in the [FORMULA] region. Using LTE models, we derive physical parameters for the features. We find the CO2 emission temperature to be [FORMULA] K. We discuss the nature of the CO2 feature at [FORMULA] and show that it can be modeled as an emission/absorption band by deviating from thermal equilibrium for the population of the [FORMULA] vibrational level. The H2O absorption spectrum is shown to arise from gas at different temperatures, but can be fit reasonably well with two components at [FORMULA] K and [FORMULA] K. The CO2 emission and hot H2O absorption temperatures are similar, suggesting that these features probe the same region of the inner envelope. We discuss the inner envelope chemistry using molecular equilibrium calculations and recent modeling work by Duari et al. (1999), and find our observations consistent with the results.

We also report the detection of the CO2 [FORMULA] ro-vibrational band in absorption towards another oxygen-rich Mira, IRC+10011.

Key words: line: identification – stars: circumstellar matter – stars: individual: R Cas, IRC+10011 – infrared: stars

* Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) with the participation of ISAS and NASA. The SWS is a joint project of SRON and MPE.

Send offprint requests to: A.J. Markwick (ajm@janus1.phy.umist.ac.uk)

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© European Southern Observatory (ESO) 2000

Online publication: July 13, 2000