New high-resolution spectra of the HR 4049, a warm supergiant with an infrared excess in the visible and near-infrared as well as the K band, are discussed. The K band spectrum shows weak absorption lines attributable to circumstellar CO. The CO lines provide an excitation temperature of 300 K and a column density of 10 to the 20th/sq cm. The chemical composition of the photosphere is derived from visible and near-infrared spectra and an LTE model atmosphere analysis. Spectroscopic indicators indicate that T(eff) is roughly 7500 K and log g is roughly 1.0. The star is very metal-poor but rich in C, N, and O. The star resembles the previously analyzed halo stars BD +39 deg 4926 and HD 46703, which appear to be evolving between the tip of the AGB and the top of the white dwarf cooling track.
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Lambert et al. (1988) studied this question.
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