A GIANO-TNG high resolution IR spectrum of the airglow emission

TL;DR

This paper presents a high-resolution, flux-calibrated IR spectrum of airglow emission from the GIANO-TNG, improving molecular line data, revealing deviations from theoretical models, and identifying new spectral lines relevant for astronomical calibration.

Contribution

It provides an improved list of OH line wavelengths and intensities, corrects previous wavelength errors, and identifies additional airglow lines, enhancing spectral calibration and molecular understanding.

Findings

Corrected wavelengths of OH Q-branch transitions.

Observed deviations in line intensities from theoretical predictions.

Identified new O2 and unidentified lines accounting for 5% of flux.

Abstract

A flux-calibrated high resolution spectrum of the airglow emission is a practical lambda-calibration reference for astronomical spectral observations. It is also useful for constraining the molecular parameters of the OH molecule and the physical conditions in the upper mesosphere. methods: We use the data collected during the first technical commissioning of the GIANO spectrograph at the Telescopio Nazionale Galileo (TNG). The high resolution (R~50,000) spectrum simultaneously covers the 0.95-2.4 micron wavelength range. Relative flux calibration is achieved by the simultaneous observation of spectrophotometric standard star. results: We derive a list of improved positions and intensities of OH infrared lines. The list includes Lambda-split doublets many of which are spectrally resolved. Compared to previous works, the new results correct errors in the wavelengths of the Q-branch transitions. The relative fluxes of OH lines from different vibrational bands show remarkable deviations from theoretical predictions: the Deltav=3,4 lines are a factor of 2 and 4 brighter than expected. We also find evidence of a significant fraction (1-4%) of OH molecules with ``non-thermal'' population of high-J levels. Finally we list wavelengths and fluxes of 153 lines not attributable to OH. Most of these can be associated to O2, while 37 lines in the H band are not identified. The O2 and unidentified lines in the H band account for ~5% of the total airglow flux in this band.