Assessment of Systematic Chromatic Errors That Impact Sub-1% Photometric Precision in Large-Area Sky Surveys

Abstract

Meeting the science goals for many current and future ground-based optical large-area sky surveys requires that the calibrated broadband photometry is both stable in time and uniform over the sky to 1% precision or better. Past and current surveys have achieved photometric precision of 1-2% by calibrating the survey's stellar photometry with repeated measurements of a large number of stars observed in multiple epochs. The calibration techniques employed by these surveys only consider the relative frame-by-frame photometric zeropoint offset and the focal plane position-dependent illumination corrections, which are independent of the source color. However, variations in the wavelength dependence of the atmospheric transmission and the instrumental throughput induce source colordependent systematic errors. These systematic errors must also be considered to achieve the most precise photometric measurements. In this paper, we examine such systematic chromatic errors using photometry from the Dark Energy Survey (DES) as an example. We first define a natural magnitude system for DES and calculate the systematic errors on stellar magnitudes, when the atmospheric transmission and instrumental throughput deviate from the natural system. We conclude that the systematic chromatic errors caused by the change of airmass in each exposure, the change of the precipitable water vapor and aerosol in the atmosphere over time, and the non-uniformity of instrumental throughput over the focal plane, can be up to 2% in some bandpasses. We then compare the calculated systematic chromatic errors with the observed DES data. For the test sample data, we correct these errors using measurements of the atmospheric transmission and instrumental throughput from auxiliary calibration systems. The residual after correction is less than 0.3%. Moreover, we calculate such systematic chromatic errors for Type Ia supernovae and elliptical galaxies and find that the chromatic errors for non-stellar objects are redshift-dependent and can be larger than those for stars at certain redshifts.

Milky Way Satellite Census. I. The Observational Selection Function for Milky Way Satellites in DES Y3 and Pan-STARRS DR1

“…The relative top-of-the-atmosphere photometric accuracy across the DES footprint is estimated to be <7 mmagfrom a comparison to Gaia (Burke et al 2018). Furthermore, DES Y3A2 includes SED-dependent chromatic corrections for each object based on an initial evaluation of the stellar spectral type (Li et al 2016;I. Sevilla-Noarbe et al 2020, in preparation).…”

Dark Energy Survey Year 3 results: galaxy sample for BAO measurement

“…The DES operations ended in 2019, after 6 yr. DES used the Blanco 4-m telescope at Cerro Tololo Inter-American Observatory (CTIO) in Chile, and observed ∼ 5000 deg 2 of the southern sky in five broadband filters, grizY, ranging from ∼ 400 to ∼ 1060 nm (Li et al 2016a;Burke et al 2018), using the DECam (Flaugher et al 2015) camera. Finally, images are processed at DES Data Management in NCSA (Morganson et al 2018).…”

Dark Energy Survey Year 3 Results: Photometric Data Set for Cosmology

“…The Dark Energy Survey (DES; DES Collaboration 2005) is a photometric survey utilizing the Dark Energy Camera (DECam; Flaugher et al 2015) on the Blanco 4 m telescope at Cerro Tololo Inter-American Observatory (CTIO) in Chile to observe~5000 deg 2 of the southern sky in five broadband filters, g, r, i, z, Y, ranging from ∼400 to~1060 nm (Li et al 2016;Burke et al 2017). 51 The primary goal of DES is to study the origin of cosmic acceleration and the nature of dark energy through four key probes: weak lensing, large-scale structure, galaxy clusters, and Type Ia supernovae (SNe).…”