J/AJ/169/84ivo://CDS.VizieR/J/AJ/169/84doi:10.26093/cds/vizier/be-59-2mCDSDauphin F.Petric A.Artigau E.Stephens A.W.Cook N.J.Businger S.,Flagey N.Marshall J.Ntampaka M.Ravindranath S.Rousseau-Nepton L.2026-07-02T11:52:28Z2025-11-21T13:15:51ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frinfrared-astronomyspectroscopySubtracting the changing sky contribution from the near-infrared (NIR) spectra of faint astronomical objects is challenging and crucial to a wide range of science cases such as estimating the velocity dispersions of dwarf galaxies, studying the gas dynamics in faint galaxies, measuring accurate redshifts, and any spectroscopic study of faint targets. Since the sky background varies with time and location, NIR spectral observations, especially those employing fiber spectrometers and targeting extended sources, require frequent sky-only observations for calibration. However, sky subtraction can be optimized with sufficient a priori knowledge of the sky's variability. In this work, we explore how to optimize sky subtraction by analyzing 1075 high-resolution NIR spectra from the Canada-France-Hawaii Telescope's SPIRou on Maunakea, and we estimate the variability of 481 hydroxyl (OH) lines. These spectra were collected during two sets of three nights dedicated to obtaining sky observations every 5.5min. During the first set, we observed how the Moon affects the NIR, which has not been accurately measured at these wavelengths. We suggest accounting for the Moon contribution at separation distances less than 10{deg} when (1) reconstructing the sky using principal component analysis, (2) observing targets at YJHK magnitudes fainter than ~15, and (3) attempting a sky subtraction better than 1%. We also identified 126 spectral doublets, or OH lines that split into at least two components, at SPIRou's resolution. In addition, we used Lomb-Scargle periodograms and Gaussian process regression to estimate that most OH lines vary on similar timescales, which provides a valuable input for IR spectroscopic survey strategies. The data (https://zenodo.org/records/13363061) and code (https://github.com/FDauphin/spirou-sky-subtraction) developed for this study are publicly available.2025AJ....169...84Dhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/AJ/169/84CatalogResearchIsServedByTAP VizieR generic servicerelated-toJ/A+A/549/A8 : Atmospheric extinction properties above Mauna Kea (Buton+, 2013)J/A+A/555/A78 : High-resolution IR airglow spectrum (Oliva+, 2013)J/A+A/568/A9 : 300-2500nm flux calibration reference spectra (Moehler+, 2014)J/A+A/581/A47 : Lines and continuum sky emission in the NIR (Oliva+, 2015)J/A+A/648/A48 : SPIRou wavelength calibration (Hobson+, 2021)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/AJ/169/84https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/AJ/169/84http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/AJ/169/84https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/AJ/169/84https://vizier.iucaa.in/viz-bin/votable?-source=J/AJ/169/84http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/AJ/169/84GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapInfrareddefaultJ/AJ/169/84/tablea1Doublet CandidatesrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintTransTransition (1)meta.notecharmu0[9975.0/22516.8] Initial Guess at line center0.1nmstat.fit.param;spect.linedoublemu1[9974.2/22513.8] Best Fit line center, closest local maxima0.1nmstat.fit.param;spect.linedoublemu2[9975.0/22516.8] Best Fit line center, next highest local max0.1nmstat.fit.param;spect.linedoubleDoubletYes/No flag noting if the line was identified as a doublet (2)meta.codechar