Accurate photometric calibration by fitting the system transmission

Abstract

Transforming the instrumental photometry of ground-based telescopes into a calibrated physical flux in a well-defined passband is a major challenge in astronomy. Along with the intrinsic instrumental difference between telescopes sharing the same filter, the effective transmission is continuously modified by the effects of the variable atmosphere of the Earth. We have developed a new approach to the absolute photometric calibration that simultaneously treats instrumental and atmospheric effects on an image-by-image basis by fitting the system transmission. This approach aims at breaking the 1% absolute photometric accuracy which limits current calibration methods for ground-based observatories. We fit the transmission, as a function of wavelength, for each image. The fit is done by comparing the instrumental fluxes of stars in the image to the synthetic photometry of the stars given their spectrum and the transmission function which have free parameters. A key element that enables this approach is the set of about 220 million low-resolution spectra measured by Gaia, which provides a large number of stellar calibrators in the image. We demonstrate the method using data from the Large Array Survey Telescope (LAST). We show that the residuals between observations and synthetic photometry of the Gaia spectra in the fitted transmission have a standard deviation $<$1% on an image-by-image basis, with no spatial and color dependencies. The median accuracy of the zero-point throughout the image is between 3-5 mmag, depending on the total image exposure. Furthermore we show that this method provides high stability over long temporal scales.

Published in A&A

References in corpus (21)

• The Gaia mission
• The Zwicky Transient Facility: Data Processing, Products, and Archive
• astroquery: An Astronomical Web-Querying Package in Python
• Photometric Response Functions of the SDSS Imager
• Pan-STARRS Photometric and Astrometric Calibration
• Gaia Data Release 3: Processing and validation of BP/RP low-resolution spectral data
• Spectrophotometric Libraries, Revised Photonic Passbands and Zero-points for UBVRI, Hipparcos and Tycho Photometry
• Gaia Data Release 3: External calibration of BP/RP low-resolution spectroscopic data
• The Palomar Transient Factory photometric calibration
• Forward Global Photometric Calibration of the Dark Energy Survey
• Toward 1% Photometry: End-to-end Calibration of Astronomical Telescopes and Detectors
• Calibrated griz magnitudes of Tycho stars: All-sky photometric calibration using bright stars
• Gaia data release 1: Principles of the photometric calibration of the G band
• Towards More Precise Survey Photometry for PanSTARRS and LSST: Measuring Directly the Optical Transmission Spectrum of the Atmosphere
• The Palomar Transient Factory photometric catalog 1.0
• catsHTM - A tool for fast accessing and cross-matching large astronomical catalogs
• The Large Array Survey Telescope -- System Overview and Performances
• Seeing-limited imaging sky surveys -- small vs. large telescopes
• The Large Array Survey Telescope -- Science Goals
• All Weather Calibration of Wide Field Optical and NIR Surveys
• The Gaia spectrophotometric standard stars survey -- IV. Results of the absolute photometry campaign

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