The Raman spectrum of the atmosphere at 23km

Ground-based optical astronomical observations supported by or in the vicinity of laser guide-star systems can be contaminated by Raman-scattered laser photons. Anticipating, alleviating, and correcting for the impact of this self-inflicted contamination requires a detailed knowledge of the pure-rotational and rotational-vibrational spectrum of the molecules in our atmosphere. We present a 15.3hr-deep combined spectrum of the 4LGSF's 589nm=509THz sodium laser beams of Paranal observatory, acquired with the ESPRESSO spectrograph at a resolution {lambda}/{Delta}{lambda}{cong.to}140000{cong.to}0.12cm^-1^ and an altitude of 23km above mean sea level. We identify 865 Raman lines over the spectral range of [3770; 7900]{AA}~[+9540;-4315]cm^-1^, with relative intensities spanning ~5 orders of magnitudes. These lines are associated to the most abundant molecules of dry air, including their isotopes: ^14^N^14^N, ^14^N^15^N, ^16^O^16^O, ^16^O^17^O, ^16^O^18^O, and ^14^C^16^O^16^O. The signal-to-noise of these observations implies that professional observatories can treat the resulting catalogue of Raman lines as exhaustive (for the detected molecules, over the observed Raman shift range) for the purpose of predicting/correcting/exploiting Raman lines in astronomical data. Our observations also reveal that the four laser units of the 4LGSF do not all lase at the same central wavelength. We measure a blueshift of +43+/-10MHz~=-50+/-10fm with respect to {lambda}4=5891.59120{AA} for LGSU1/2, and +94+/-10MHz=-109+/-10fm for LGSU3/4. These offsets, including the difference of ~50MHz between LGSU1/2 and LGSU3/4, are larger than the observed 4LGSF spectral stability of +/-3MHz over hours. They remain well within the operational requirements for creating artificial laser guide-stars, but hinder the assessment of the radial velocity accuracy of ESPRESSO at the required level of 10m/s. Altogether, our observations demonstrate how Raman lines can be exploited by professional observatories as highly-accurate, on-sky wavelength references.

Identifier
Source https://dc.g-vo.org/rr/q/lp/custom/CDS.VizieR/J/other/PhRvR/5.B3145
Related Identifier https://cdsarc.cds.unistra.fr/viz-bin/cat/J/other/PhRvR/5.B3145
Related Identifier http://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/other/PhRvR/5.B3145
Metadata Access http://dc.g-vo.org/rr/q/pmh/pubreg.xml?verb=GetRecord&metadataPrefix=oai_b2find&identifier=ivo://CDS.VizieR/J/other/PhRvR/5.B3145
Provenance
Creator Vogt F.P.A.; Mehner A.; Figueira P.; Yu S.; Kerber F.; Pfrommer T.,Hackenberg W.; Bonaccini Calia D.
Publisher CDS
Publication Year 2023
Rights https://cds.unistra.fr/vizier-org/licences_vizier.html
OpenAccess true
Contact CDS support team <cds-question(at)unistra.fr>
Representation
Resource Type Dataset; AstroObjects
Discipline Astrophysics and Astronomy; Interdisciplinary Astronomy; Natural Sciences; Observational Astronomy; Physics; Solar System Astronomy