Spectroscopy of the Post-AGB Disk around HR 4049
Abstract
High-resolution infrared spectroscopy in the 2.3-4.6 μm region is reported for the peculiar star HR 4049. HR 4049 has severe depletion of refractory elements but solar abundances of volatile elements suggesting a winnowing process. 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 in emission through the 3 and 4.6 μm region and in absorption in the 2 μm region. The 4.6 μm spectrum shows a rich 'forest' of emission lines. All the spectral lines observed in the 2.3-4.6 μm spectrum are shown to be circumstellar in origin. The presence of OH and H2O lines confirm the oxygen-rich nature of the circumstellar gas. HR 4049 has an oxygen-rich circumbinary disk surrounded by a carbon-rich circumstellar shell. The emission and absorption line profiles show that the gas is located in a thin, rotating layer near the circumbinary dust ring. In addition to rotation, gas in the ring is also flowing outward with a velocity of at least 1 km s-1. A model is described where the gas is driven from the grains in a winnowing process producing the observed surface abundances. Contrary to prior reports, the HR 4049 carbon and oxygen isotopic abundances are typical for an AGB or post-AGB star. 12C/13C=9±6 and 16O/17O>200. Assuming that the binary orbit is co-planer with the disk, the mass of the post-AGB star is 0.58 solar mass and the mass of the unseen companion is 0.34 solar mass.
- Publication:
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American Astronomical Society Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AAS...209.8102H