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GPS Measurements of Precipitable Water Vapor Can Improve Survey Calibration: A Demonstration from KPNO and the Mayall z-band Legacy Survey

Wood-Vasey, W. M. and Perrefort, Daniel and Baker, Ashley D. (2022) GPS Measurements of Precipitable Water Vapor Can Improve Survey Calibration: A Demonstration from KPNO and the Mayall z-band Legacy Survey. Astronomical Journal, 163 (6). Art. No. 283. ISSN 0004-6256. doi:10.3847/1538-3881/ac63bb.

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Dual-band Global Positioning Satellite (GPS) measurements of precipitable water vapor (PWV) at the Kitt Peak National Observatory predict the overall per-image sensitivity of the Mayall z-band Legacy Survey (MzLS). The per-image variation in the brightness of individual stars is strongly correlated with the measured PWV and the color of the star. Synthetic stellar spectra through TAPAS transmission models successfully predict the observed PWV-induced photometric variation. We find that PWV absorption can be well approximated by a linear relationship with (airmass × PWV)^(0.6) and present an update on the traditional treatment in the literature. The MzLS zero-point sensitivity in electrons s⁻¹ varies with a normalized-mean absolute deviation of 61 mmag. PWV variation accounts 23 mmag of this zero-point variation. The MzLS per-image absolute sensitivity decreases by 40 mmag per effective mm of PWV. The overall gray offset portion of this variation is corrected by the calibration to a reference catalog. But the relative calibration error between blue (r − z r − z) stars increases by 0.3–2 mmag per effective mm of PWV. We argue that GPS systems provide more precise PWV measurements than using differential measurements of stars of different colors and recommend that observatories install dual-band GPS as a low-maintenance, low-cost, auxiliary calibration system. We extend our results of the need for well-calibrated PWV measurements by presenting the calculations of the PWV photometric impact on three science cases of interest: stellar photometry, supernova cosmology, and quasar identification and variability.

Item Type:Article
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URLURL TypeDescription Paper
Wood-Vasey, W. M.0000-0001-7113-1233
Perrefort, Daniel0000-0002-3988-4881
Baker, Ashley D.0000-0002-6525-7013
Additional Information:© 2022. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Received 2020 October 26; revised 2022 March 31; accepted 2022 April 1; published 2022 May 20. Our thanks to Dustin Lang, David Schegel, Arjun Dey, and the DECALS team for rapid and helpful responses to questions we had in the analysis of this data. Part of the catalyst for this paper was a conversation between M.W.-V. and D. Schlegel at the 20th Anniversary Subaru Meeting hosted by the NOAJ in Waikola, Hawai'i. Our thanks to the anonymous referee, whose comments improved this manuscript—particularly the suggestion to look more carefully at potential variation in the effective gain. This work was supported in part by the US Department of Energy Office of Science under DE-SC0007914. The Legacy Surveys consist of three individual and complementary projects: the Dark Energy Camera Legacy Survey (DECaLS; NOAO Proposal ID # 2014B-0404; PIs: David Schlegel and Arjun Dey), the Beijing-Arizona Sky Survey (BASS; NOAO Proposal ID # 2015A-0801; PIs: Zhou Xu and Xiaohui Fan), and the Mayall z-band Legacy Survey (MzLS; NOAO Proposal ID # 2016A-0453; PI: Arjun Dey). DECaLS, BASS, and MzLS together include data obtained, respectively, at the Blanco telescope, Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatory (NOAO); the Bok telescope, Steward Observatory, University of Arizona; and the Mayall telescope, Kitt Peak National Observatory, NOAO. The Legacy Surveys project is honored to be permitted to conduct astronomical research on Iolkam Du'ag (Kitt Peak), a mountain with particular significance to the Tohono O'odham Nation. This work is based in part on observations taken at Kitt Peak National Observatory, National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation.
Funding AgencyGrant Number
Department of Energy (DOE)DE-SC0007914
Subject Keywords:Earth atmosphere; Flux calibration; Water vapor; Astronomical methods; Sky surveys; Exoplanet detection methods; Type Ia supernovae; Observational cosmology; Quasars
Issue or Number:6
Classification Code:Unified Astronomy Thesaurus concepts: Earth atmosphere (437); Flux calibration (544); Water vapor (1791); Astronomical methods (1043); Sky surveys (1464); Exoplanet detection methods (489); Type Ia supernovae (1728); Observational cosmology (1146); Quasar
Record Number:CaltechAUTHORS:20220523-165021000
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Official Citation:W. M. Wood-Vasey et al 2022 AJ 163 283
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:114879
Deposited By: George Porter
Deposited On:24 May 2022 17:05
Last Modified:24 May 2022 17:05

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