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

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

Abstract

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 ro-vibrational band at . The emission features are the and ro-vibrational transitions at 13.87 and respectively. The water absorption spectrum shows the and ro-vibrational bands in the region. Using LTE models, we derive physical parameters for the features. We find the CO₂ emission temperature to be K. We discuss the nature of the CO₂ feature at and show that it can be modeled as an emission/absorption band by deviating from thermal equilibrium for the population of the 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 K and 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 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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Contents

• 1. Introduction
• 2. Observations
• 3. Spectral modeling
  • 3.1. Absorption spectra
  • 3.2. Emission spectra
• 4. Results and discussion
  • 4.1. CO₂
  • 4.2. H₂O
  • 4.3. Inner envelope chemistry
• 5. Conclusion
• Acknowledgements
• References

© European Southern Observatory (ESO) 2000

Online publication: July 13, 2000
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