F. P. A. Vogt, F. Kerber, A. Mehner, S. Yu, T. Pfrommer, G. Lo Curto, P. Figueira, D. Parraguez, F. Pepe, D. Mégevand, M. Riva, P. Di Marcantonio, C. Lovis, M. Amate, P. Molaro, A. Cabral, M.-R. Osorio

Abstract
Raman scattering enables unforeseen uses for the laser guide-star system of the Very Large Telescope. Here, we present the observation of one up-link sodium laser beam acquired with the ESPRESSO spectrograph at a resolution λ/∆λ ~140 000. In 900 s on source, we detect the pure rotational Raman lines of ¹⁶O₂, ¹⁴N₂, and ¹⁴N¹⁵N (tentatively) up to rotational quantum numbers J of 27, 24, and 9, respectively. We detect the ¹⁶O₂ fine-structure lines induced by the interaction of the electronic spin S and end-over-end rotational angular momentum N in the electronic ground state of this molecule up to N=9 . The same spectrum also reveals the ν_{1 ←0} rotational-vibrational Q-branch for ¹⁶O₂ and ¹⁴N₂. These observations demonstrate the potential of using laser guide-star systems as accurate calibration sources for characterizing new astronomical spectrographs.

Keywords
Astrophysics - Instrumentation and Methods for Astrophysics; Physics - Atmospheric and Oceanic Physics; Physics - Instrumentation and Detectors

Physical Review Letters
Volume 123, Issue 6
2019 August

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