Transmission of the AtmosPhere for AStronomical data: TAPAS upgrade

Abstract

State-of-the-art molecular databases and realistic global atmospheric models allow to predict accurate atmospheric transmittance spectra. The TAPAS online service provides atmospheric transmittance spectra of the most important species as well as Rayleigh extinction, adapted to any observing location, date, and direction. We describe recent updates, improvements, and additional tools. TAPAS is interpolating in location in the atmospheric profiles of temperature, pressure, H$_2$O, O$_2$ and O$_3$ extracted from the ECMWF and produced by Arletty, a Data Terra/AERIS/ESPRI product, supplemented by auxiliary climatological models for additional species. The transmittance spectra are computed with the LBLRTM code. The resolution is chosen to ensure that the shapes of all absorption lines are reproduced for each species. Major improvements are: $\bullet$ the extension of the wavelength range in the near-UV down to 300 nm; in the near-IR up to 3500 nm; $\bullet$ the use of HITRAN2020; $\bullet$ the addition of NO$_2$, to complement H$_2$O, O$_2$, O$_3$, N$_2$O, CO$_2$ and CH$_4$; $\bullet$ an increased accessibility; $\bullet$ the possibility to force the total H$_2$O column to match the one measured at the observatory. We show O3 absorption in the near-UV and near-IR and NO2 absorption in the visible. We illustrate the quality of TAPAS by means of comparisons between models and ESO/VLT/CRIRES recorded spectra of a hot star with spectral resolution 130,000, in two intervals with strong H$_2$O, NO$_2$, CO$_2$ and CH$_4$ absorption. We describe the measurement of an instrumental Line Spread Function (LSF) based on TAPAS O$_2$ lines and a method using the Singular Value Decomposition technique that can be made entirely automated. TAPAS can be used to improve the wavelength and to measure the LSF in regions where telluric features are present. The extended wavelength range will be particularly useful for future or recent spectrographs in the near-UV and in the near-infrared.