The structure of protoplanetary disks surrounding three young intermediate mass stars -: I.: Resolving the disk rotation in the [OI] 6300 Å line

We present high-spectral-resolution, optical spectra of three young, intermediate-mass stars, in all of which we spectrally resolve the 6300 angstrom [OI] emission line. Two of these have a double-peaked line-profile. We attempt to fit these data using a simple model of [OI] emission, which is generated by photo-dissociation of OH molecules, in the upper layer of a circumstellar disk, by stellar UV radiation. We translate the Doppler-broadened [OI] emission line profile, into a measure of emission, as a function of distance from the central star. The resulting spectra are in agreement with the expected disk shapes derived from their spectral energy distribution. We find evidence for shadowing by an inner rim in the disk surrounding HD 101412, and observe a flaring disk structure in HD 179218, while the [OI] spectrum of HD 135344 B is more complex. The [OI] emission starts for all three targets at velocities corresponding to their dust sublimation radius and extends up to radii of 10-90 AU. This shows that this method can be a valuable tool in the future investigation of circumstellar disks.