2005A&A...436..209A

We present high spectral-resolution optical spectra of 49 Herbig Ae/Be stars in a search for the [OI] 6300 line. The vast majority of the stars in our sample show narrow (FWHM<100km/s) emission lines, centered on the stellar radial velocity. In only three sources is the feature much broader (∼400km/s), and strongly blueshifted (-200km/s) compared to the stellar radial velocity. Some stars in our sample show double-peaked line profiles, with peak-to-peak separations of ∼10km/s. The presence and strength of the [OI] line emission appears to be correlated with the far-infrared energy distribution of each source: stars with a strong excess at 60µm have in general stronger [OI] emission than stars with weaker 60µm excesses. We interpret these narrow [OI] 6300 line profiles as arising in the surface layers of the protoplanetary disks surrounding Herbig Ae/Be stars. A simple model for [OI] 6300 line emission due to the photodissociation of OH molecules shows that our results are in quantitative agreement with that expected from the emission of a flared disk if the fractional OH abundance is ∼5x10^–7.