Comparison of VLT/X-shooter OH and O_2 rotational temperatures with consideration of TIMED/SABER emission and temperature profiles

摘要

Rotational temperatures Trot derived from lines of the same OH band are an important method to study the dynamics and long-term trends in 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 v0, 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 O_2b(0-1), which peaks at about 94 to 95 km, and O_2a(0-0) with an emission peak at about 90 km. The latter altitude is reached in the second half of the night after a rise of several km because of the decay of a daytime population of excited O_2.