High-Spatial- and High-Spectral-Resolution Observations of the Inhomogeneous Outer Atmosphere of the M Giant BK Vir

We present high-spatial- and high-spectral-resolution observations of the normal M-type AGB star BK Vir using the AMBER instrument at the Very Large Telescope Interferometer. AMBER's high spatial resolution (9.5 mas) and high spectral resolution (lambda/Delta lambda = 12000) enable us to probe the inhomogeneous structure of the atmosphere using the CO first-overtone lines near 2.3 mu m. The AMBER data in the CO lines reveal the presence of inhomogeneous CO layers, which are much more extended than predicted by hydrostatic photospheric models. These AMBER observations are the first to spatially resolve the "warm molecular envelope" toward AGB stars in individual CO lines.