  We present high spectral resolution (R = 30000) spectroscopic observations of
the SiO fundamental lines near 8.1 micron in 16 bright red giants and red
supergiants using VLT/VISIR. Our sample consists of seven normal K--M giants,
three Mira stars, three optically bright red supergiants, two dusty red
supergiants, and the enigmatic object GCIRS3 near the Galactic center. We
detected SiO fundamental lines in all of our program stars except for GCIRS3.
The SiO lines in normal K and M giants as well as optically bright red
supergiants do not show P-Cyg profiles or blueshifts, which means the absence
of systematic outflows in the SiO line forming region. On the other hand, we
detected P-Cyg profiles in the SiO lines in the dusty red supergiants VY CMa
and VX Sgr (with the latter being a new detection), which suggest outflow
velocities of 27 and 17 km/s, respectively. We derived basic stellar parameters
(effective temperature, surface gravity, luminosity, and mass) for the normal
K--M giants and optically bright red supergiants in our sample and compared the
observed VISIR spectra with synthetic spectra predicted from MARCS photospheric
models. Most of the SiO lines observed in the program stars warmer than ~3400 K
are reasonably reproduced by the MARCS models, which allowed us to estimate the
silicon abundance as well as the 28Si/29Si and 28Si/30Si ratios. However, we
detected possible absorption excess in some SiO lines. Moreover, the SiO lines
in the cooler red giants and red supergiant cannot be explained by the MARCS
models at all even if the dust emission is taken into account. This
disagreement may be a signature of the dense, extended molecular outer
atmosphere.
