Infrared high-resolution spectroscopy of post-AGB circumstellar disks. I. HR 4049: The winnowing flow observed?

High-resolution infrared spectroscopy in the 2.3Y4.6 mu m region is reported for the peculiar A supergiant, single-lined spectroscopic binary HR 4049. Lines from the CO fundamental and first overtone, OH fundamental, and several H2O vibration-rotation transitions have been observed in the near-infrared spectrum. The spectrum of HR 4049 appears principally in emission through the 3 and 4.6 mu m region and in absorption in the 2 mu m region. The 4.6 mu m spectrum shows a rich forest'' of emission lines. All the spectral lines observed in the 2.3Y4.6 mu m spectrum are shown to be circumbinary in origin. The presence of OH and H2O lines confirm the oxygen-rich nature of the circumbinary gas, which is in contrast to the previously detected carbon-rich material. The emission and absorption line profiles show that the circumbinary gas is located in a thin, rotating layer near the dust disk. The properties of the dust and gas circumbinary disk and the spectroscopic orbit yield masses for the individual stars, M-AI similar to 0.58 M-circle dot and M-secondary similar to 0.34 M-circle dot. Gas in the disk also has an outward flow with a velocity of greater than or similar to kms-(1). The severe depletion of refractory elements but near-solar abundances of volatile elements observed in HR 4049 results from abundance winnowing. The separation of the volatiles from the grains in the disk and the subsequent accretion by the star are discussed. Contrary to prior reports, the HR 4049 carbon and oxygen isotopic abundances are typical AGB values, C-12/C-13 =6(-4)(+9) and O-16/O-17 > 200.