  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.
