Volume 394, Number 2, November I 2002
|Page(s)||L27 - L30|
|Published online||15 October 2002|
Letter to the Editor
Detection of abundant solid CO in the disk around CRBR 2422.8-3423 *
Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
2 Leiden Observatory, PO Box 9513, 2300 RA, Leiden, The Netherlands
3 Astrochimie Expérimentale, Institut d'Astrophysique Spatiale, Université Paris-Sud, Bât. 121, 91405 Orsay, France
Corresponding author: W. F. Thi, firstname.lastname@example.org
Accepted: 17 September 2002
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 . The spectrum shows strong solid CO absorption, with a lower limit on the column density of 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 only a small fraction of the total solid CO, based on the weakness of solid CO absorption toward nearby sources and the absence of gaseous C18O emission 30´´ south. Gas-phase ro-vibrational CO absorption lines are also detected with a mean temperature of K. The average gas/solid CO ratio is ~1 along the line of sight. For an estimated inclination of 20°, 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-, an indicator of thermal/ultraviolet processing of the ice mantle. By contrast, the warm gaseous CO likely originates closer to the star.
Key words: star formation / ISM: dust, extinction / molecules / abundances / infrared: ISM: lines and bands
© ESO, 2002
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