A Search for CO Absorption Bands in IUE Spectra of Cool Stars

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Session 46 -- Late Type Stars
Display presentation, Wednesday, 9:20-6:30, Heller Lounge Room

[46.12] A Search for CO Absorption Bands in IUE Spectra of Cool Stars

S. Gessner (USRA), K. Carpenter (NASA-GSFC), R. Robinson (CSC)

Observations of the red supergiant (M2 Iab) $\alpha$~Ori with the Goddard High Resolution Spectrograph (GHRS) onboard the Hubble Space Telescope (HST) have provided an unambiguous detection of a far-UV continuum on which are superposed strong molecular absorption bands (Carpenter 1991, ASP Conf. Ser. 26, p. 17). The continuum is formed in the stellar chromosphere. The absorption bands, which appear in the 1300 - 1600 \AA\ spectral region, have been identified with the (n,0) bands (n=0,...,8) of the 4th-positive A-X system of CO and are likely formed in the circumstellar shell. Comparison of these GHRS data with archival IUE spectra indicates that both the continuum and the CO absorption features can be seen with IUE, especially if multiple IUE spectra, reduced with the post-1981 IUESIPS extraction procedure (i.e., with an oversampling slit), are carefully co-added to increase the signal-to-noise over that obtainable with a single spectrum. We have therefore begun a program, utilizing both new and archival IUE spectra, to survey other cool, low-gravity stars for the presence of these two new chromospheric and circumstellar shell diagnostics. We hope to identify promising targets for examination with HST spectrographs at the higher resolution and signal-to-noise needed for quantitative analysis. The initial results of this IUE survey are presented here.

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