  Rotational temperatures Trot derived from lines of the same OH band are an
important method to study the mesopause region near 87 km. To measure realistic
temperatures, the rotational level populations have to be in local
thermodynamic equilibrium (LTE). However, this might not be fulfilled,
especially at high emission altitudes. In order to quantify possible non-LTE
contributions to the OH Trot as a function of the upper vibrational level v',
we studied a sample of 343 echelle spectra taken with the X-shooter
spectrograph at the Very Large Telescope at Cerro Paranal in Chile. These data
allowed us to analyse 25 OH bands in each spectrum. Moreover, we could measure
lines of O2b(0-1), which peaks at 94 to 95 km, and O2a(0-0) with an emission
peak at about 90 km. Since the radiative lifetimes are relatively long, the
derived O2 Trot are not significantly affected by non-LTE contributions. For a
comparison with OH, the differences in the emission profiles were corrected by
using OH emission, O2a(0-0) emission, and CO2-based temperature profile data
from the multi-channel radiometer SABER on the TIMED satellite. For a reference
profile at 90 km, we found a good agreement of the O2 with the SABER-related
temperatures, whereas the OH temperatures, especially for the high and even v',
showed significant excesses with a maximum of more than 10 K for v' = 8. We
could also find a nocturnal trend towards higher non-LTE effects, particularly
for high v'.
