Detection of abundant solid CO in the disk around CRBR 2422.8-3423
  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. 
W.F. Thi (1 and 2), K.M. Pontoppidan (2), E.F. van Dishoeck (2), E.   Dartois (3) and L. d'Hendecourt (3) ((1) University Co...