Non-thermal emission in the atmosphere above Mauna Kea

Abstract

We present 1–2.5 µm spectra of the atmosphere above Mauna Kea. The emission in this region is chiefly non-thermal radiation from excited molecules in the upper atmosphere, but above ∼ 2.3 µm the thermal contribution from the telescope and surroundings dominates. The most important component of the non-thermal emission is from vibrational–rotational transitions of the hydroxyl radical, OH−. In addition to identifying these lines we examine the temporal and spatial variation of this emission, comparing the results with theories of the origin of the variation. We model the effect of this changing background on an hour-long sequence of observations of different exposure times and demonstrate the importance of frequent sky sampling for observations of extended objects.