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We present high resolution (R = 100,000) L-band spectroscopy of 11 HerbigAeBe stars with circumstellar disks. The observations were obtained with theVLT/CRIRES to detect hot water and hydroxyl radical emission lines previouslydetected in disks around T Tauri stars. OH emission lines are detected towards4 disks. The OH P4.5 (1+,1-) doublet is spectrally resolved as well as thevelocity profile of each component of the doublet. Its characteristicdouble-peak profile demonstrates that the gas is in Keplerian rotation andpoints to an emitting region extending out to ~ 15-30 AU. The OH, emissioncorrelates with disk geometry as it is mostly detected towards flaring disks.None of the Herbig stars analyzed here show evidence of hot water vapor at asensitivity similar to that of the OH lines. The non-detection of hot watervapor emission indicates that the atmosphere of disks around Herbig AeBe starsare depleted of water molecules. Assuming LTE and optically thin emission wederive a lower limit to the OH/H2O column density ratio > 1 - 25 in contrast toT Tauri disks for which the column density ratio is 0.3 -- 0.4.

Water depletion in the disk atmosphere of Herbig AeBe stars