  We present spatially resolved high-spectral resolution K-band observations of
the red supergiant Betelgeuse (alpha Ori) using AMBER at the Very Large
Telescope Interferometer (VLTI). Betelgeuse was observed between 2.28 and 2.31
micron using baselines of 16, 32, and 48m with spectral resolutions of 4800 --
12000. Spectrally dispersed interferograms have been obtained in the 2nd, 3rd,
and 5th lobes, which represents the highest spatial resolution (9 mas) achieved
for Betelgeuse, corresponding to 5 resolution elements over its stellar disk.
The AMBER data in the continuum can be reasonably fitted by a uniform disk with
a diameter of 43.19+/-0.03 mas or a limb-darkening disk with 43.56+/-0.06 mas.
The K-band interferometric data taken at various epochs suggest that Betelgeuse
seen in the continuum shows much smaller deviations from the above
uniform/limb-darkened disk than predicted by 3-D convection simulations. On the
other hand, our AMBER data in the CO lines reveal that the blue and red wings
of the CO lines originate in spatially distinct regions over the stellar disk,
indicating an inhomogeneous velocity field. Our AMBER data in the CO lines can
be roughly explained by a simple model, in which a patch of CO gas is moving
outward or inward at velocities of 10--15 km s^-1, while the CO gas in the
remaining region in the atmosphere is moving in the opposite direction at the
same velocities. The AMBER data are also consistent with the presence of warm
molecular layers at ~1.4--1.5 Rstar with a CO column density of ~1 x 10^20
cm^-2. Our AMBER observations of Betelgeuse are the first spatially resolved
study of the so-called macroturbulence in a stellar atmosphere other than the
Sun. The spatially resolved CO gas motion is likely to be related to convective
motion or intermittent mass ejections in clumps or arcs.

Solar and Stellar Astrophysics