# Sky Variability in the y Band at the LSST Site

 Title: Sky Variability in the y Band at the LSST Site Author: High, F. William; Stubbs, Christopher William; Gilmore, David Kirk; Tonry, John L.; Stalder, Brian A. Note: Order does not necessarily reflect citation order of authors. Citation: High, F. William, Christopher William Stubbs, Brian A. Stalder, David Kirk Gilmore, and John L. Tonry. 2010. Sky variability in the y band at the LSST site. Publications of the Astronomical Society of the Pacific 122(892): 722–730. Full Text & Related Files: 1002.3637v2.pdf (650.6Kb; PDF) Abstract: We have measured spatial and temporal variability in the y-band sky brightness over the course of four nights above Cerro Tololo near Cerro Pachon, Chile, the planned site for the Large Synoptic Survey Telescope (LSST). Our wide-angle camera lens provided a 41° field of view and a 145" pixel scale. We minimized potential system throughput differences by deploying a deep-depletion CCD and a filter that matches the proposed LSST $$y_3$$ band (970 –1030 nm). Images of the sky exhibited coherent wave structure, attributable to atmospheric gravity waves at 90 km altitude, creating 3%–4% rms spatial sky flux variability on scales of about 2° and larger. Over the course of a full night, the $$y_3$$ band additionally showed highly coherent temporal variability of up to a factor of 2 in flux. We estimate the mean absolute sky level to be approximately $$y_3 = 17.8 mag(Vega)$$, or $$y_3 = 18.3 mag(AB)$$. While our observations were made through a $$y_3$$ filter, the relative sky brightness variability should hold for all proposed y bands, whereas the absolute levels should more strongly depend on spectral response. The spatial variability presents a challenge to wide-field cameras that require illumination correction strategies that make use of stacked sky flats. The temporal variability may warrant an adaptive y band imaging strategy for LSST, to take advantage of times when the sky is darkest. Published Version: doi:10.1086/653715 Other Sources: http://arxiv.org/abs/1002.3637 Terms of Use: This article is made available under the terms and conditions applicable to Open Access Policy Articles, as set forth at http://nrs.harvard.edu/urn-3:HUL.InstRepos:dash.current.terms-of-use#OAP Citable link to this page: http://nrs.harvard.edu/urn-3:HUL.InstRepos:10226787 Downloads of this work: