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Detection of abundant solid CO in the disk around CRBR 2422.8-3423

W. F. Thi·K. M. Pontoppidan·E. F. van Dishoeck·E. Dartois·L. d'Hendecourt
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Abstract

We present direct evidence for CO freeze-out in a circumstellar disk around the edge-on class I object CRBR 2422.8-3423, observed in the M band with VLT-ISAAC at a resolving power R~10,000. The spectrum shows strong solid CO absorption, with a lower limit on the column density of 2.2E18 cm-2. The solid CO column is the highest observed so far, including high-mass protostars and background field stars. Absorption by foreground cloud material likely accounts for less than 10% percent of the total solid CO, based on the weakness of solid CO absorption toward nearby sources and the absence of gaseous C18O J=2-1 emission 30'' south. Gas-phase ro-vibrational CO absorption lines are also detected with a mean temperature of 50 +/-10 K. The average gas/solid CO ratio is ~1 along the line of sight. For an estimated inclination of 20 +/- 5 degree, the solid CO absorption originates mostly in the cold, shielded outer part of the flaring disk, consistent with the predominance of apolar solid CO in the spectrum and the non-detection of solid OCN-, a thermal/ultraviolet processing of the ice mantle. The gaseous CO comes from the warm upper layers closer to the star.

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W. F. Thi, K. M. Pontoppidan, E. F. van Dishoeck, E. Dartois, L. d'Hendecourt. 2002-09-20. Detection of abundant solid CO in the disk around CRBR 2422.8-3423. https://doi.org/10.1051/0004-6361%3A20021353

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