  Aims. We intend to spatially and spectrally resolve the [O I] emission region
in two nearby Herbig stars.
  Methods. We present high-resolution (R = 80,000) VLT/UVES echelle spectra of
the [O I] 6300A line in the Herbig Ae/Be stars HD 97048 and HD 100546. Apart
from the spectral signature, also the spatial extent of the [O I] emission
region is investigated. For both stars, we have obtained spectra with the slit
positioned at different position angles on the sky.
  Results. The [O I] emission region of HD 100546 appears to be coinciding with
the dust disk, its major axis located at 150+/-11 degrees east of north. The SE
part of the disk moves towards the observer, while the NW side is redshifted.
The [O I] emission region rotates counterclockwise around the central star. For
HD 97048, the position angle of the emission region is 160+/-19 degrees east of
north, which is the first determination of this angle in the literature. The
southern parts of the disk are blueshifted, the northern side moves away from
us. Our data support the idea that a gap is present at 10AU in the disk of HD
100546. Such a gap is likely planet-induced. We estimate the mass and orbital
radius of this hypothetical companion responsible for this gap to be 20 Jupiter
masses and 6.5 AU respectively.
  Conclusions. Based on temporal changes in the [O I] line profile, we conclude
that inhomogeneities are present in the [O I] emission region of HD 100546.
These ``clumps'' could be in resonance with the suggested companion, orbiting
the central star in about 11 yr. If confirmed, these observations could point
to the existence of an object straddling the line between giant planet and
brown dwarf in a system as young as 10 million years.
