Astronomy and Astrophysics, volume 359, 1162-1168 (2000/7-3)
ISO-SWS Observations of CO2 and H2O in R Cassiopeiae.
MARKWICK A.J. and MILLAR T.J.
Abstract (from CDS):
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 0110-0000 ro-vibrational band at 14.97µm . The emission features are the 1000-0110 and 1110-0220 ro-vibrational transitions at 13.87 and 13.48µm respectively. The water absorption spectrum shows the ν1 and ν3 ro-vibrational bands in the 2.75-3µm region. Using LTE models, we derive physical parameters for the features. We find the CO2 emission temperature to be ∼1100 K. We discuss the nature of the CO2 feature at 15µm and show that it can be modeled as an emission/absorption band by deviating from thermal equilibrium for the population of the 0110 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 T=950 K and T=250 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 0110-0000 ro-vibrational band in absorption towards another oxygen-rich Mira, IRC+10011.