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Session 67 - Stars: Evolution, Atmospheres, Intrinsic.
Display session, Thursday, June 11
We report high-resolution (R\sim 5\times10^4) spectra of the 2143 cm^-1 (4.7 \mum) interval---containing lines from the fundamental (\Delta v =1) bands of carbon monoxide---in the Sun and other late-type stars, obtained with the \footnotesize PHOENIX cryogenic infrared spectrometer. The solar work was conducted at the McMath-Pierce telescope during the period 21--26 April 1997, while the stellar observations were obtained on the night of 6 December 1997 at the Kitt Peak 2.1-m.
Comparisons of spatially-averaged spectra from the long-slit observations of the Sun with very high-resolution Fourier transform spectrometer scans permitted an evalution of the \footnotesize PHOENIX instrumental profile (affected by flexing of the grating owing to unequal thermal coefficients of the epoxy replica and the silicon substrate). The profile information subsequently was applied in comparisons of the stellar data sets with CO spectra synthesized using a variety of prototype thermal structure models. On the stellar side, we concentrated on bright K-type giants whose broad CO profiles are fully resolved at \footnotesize PHOENIX resolution. Our intent was to test the degree of thermal heterogeneity in the outer layers of the red giant atmospheres; analogous to the ``thermal bifurcation'' effects deduced in the solar context (namely, the dichotomy between classical hot chromosphere and the controversial cool ``COmosphere'').
Our spectral analyses provide a preview of the power of \footnotesize PHOENIX for high-resolution infrared spectroscopy of stars; to be realized in the coming months when the original grating is replaced with an improved version. [-2mm]
The observations were obtained at the National Optical Astronomy Observatories, which is operated by AURA, Inc., under a cooperative agreement with the National Science Foundation. This work was supported by NSF grant AST-9618505.
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