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Title: Photometric Characterization of the Dark Energy Camera

We characterize the variation in photometric response of the Dark Energy Camera (DECam) across its 520 Mpix science array during 4 years of operation. These variations are measured using high signal-to-noise aperture photometry of >10 7 stellar images in thousands of exposures of a few selected fields, with the telescope dithered to move the sources around the array. A calibration procedure based on these results brings the rms variation in aperture magnitudes of bright stars on cloudless nights down to 2–3 mmag, with <1 mmag of correlated photometric errors for stars separated by ≥20''. On cloudless nights, any departures of the exposure zeropoints from a secant airmass law exceeding 1 mmag are plausibly attributable to spatial/temporal variations in aperture corrections. These variations can be inferred and corrected by measuring the fraction of stellar light in an annulus between 6'' and 8'' diameter. Key elements of this calibration include: correction of amplifier nonlinearities; distinguishing pixel-area variations and stray light from quantum-efficiency variations in the flat fields; field-dependent color corrections; and the use of an aperture-correction proxy. The DECam response pattern across the 2° field drifts over months by up to ±9 mmag, in a nearly wavelength-independent low-order pattern. Here, we findmore » no fundamental barriers to pushing global photometric calibrations toward mmag accuracy.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [6] ;  [7] ;  [5] ;  [4] ;  [2] ;  [5] ;  [5]
  1. Univ. of Pennsylvania, Philadelphia, PA (United States)
  2. National Optical Astronomy Observatory, La Serena (Chile)
  3. Princeton Univ., Princeton, NJ (United States)
  4. Stanford Univ., Stanford, CA (United States); SLAC National Accelerator Lab., Menlo Park, CA (United States)
  5. Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
  6. Univ. of Illinois, Urbana, IL (United States); National Center for Supercomputing Applications, Urbana, IL (United States)
  7. National Center for Supercomputing Applications, Urbana, IL (United States)
Publication Date:
Grant/Contract Number:
AC02-76SF00515; SC0007901; AST-1615555
Type:
Accepted Manuscript
Journal Name:
Publications of the Astronomical Society of the Pacific
Additional Journal Information:
Journal Volume: 130; Journal Issue: 987; Journal ID: ISSN 0004-6280
Publisher:
Astronomical Society of the Pacific
Research Org:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; instrumentation: detectors; methods: data analysis; techniques: photometric
OSTI Identifier:
1434675

Bernstein, G. M., Abbott, T. M. C., Armstrong, R., Burke, D. L., Diehl, H. T., Gruendl, R. A., Johnson, M. D., Li, T. S., Rykoff, E. S., Walker, A. R., Wester, W., and Yanny, B.. Photometric Characterization of the Dark Energy Camera. United States: N. p., Web. doi:10.1088/1538-3873/aaa753.
Bernstein, G. M., Abbott, T. M. C., Armstrong, R., Burke, D. L., Diehl, H. T., Gruendl, R. A., Johnson, M. D., Li, T. S., Rykoff, E. S., Walker, A. R., Wester, W., & Yanny, B.. Photometric Characterization of the Dark Energy Camera. United States. doi:10.1088/1538-3873/aaa753.
Bernstein, G. M., Abbott, T. M. C., Armstrong, R., Burke, D. L., Diehl, H. T., Gruendl, R. A., Johnson, M. D., Li, T. S., Rykoff, E. S., Walker, A. R., Wester, W., and Yanny, B.. 2018. "Photometric Characterization of the Dark Energy Camera". United States. doi:10.1088/1538-3873/aaa753.
@article{osti_1434675,
title = {Photometric Characterization of the Dark Energy Camera},
author = {Bernstein, G. M. and Abbott, T. M. C. and Armstrong, R. and Burke, D. L. and Diehl, H. T. and Gruendl, R. A. and Johnson, M. D. and Li, T. S. and Rykoff, E. S. and Walker, A. R. and Wester, W. and Yanny, B.},
abstractNote = {We characterize the variation in photometric response of the Dark Energy Camera (DECam) across its 520 Mpix science array during 4 years of operation. These variations are measured using high signal-to-noise aperture photometry of >107 stellar images in thousands of exposures of a few selected fields, with the telescope dithered to move the sources around the array. A calibration procedure based on these results brings the rms variation in aperture magnitudes of bright stars on cloudless nights down to 2–3 mmag, with <1 mmag of correlated photometric errors for stars separated by ≥20''. On cloudless nights, any departures of the exposure zeropoints from a secant airmass law exceeding 1 mmag are plausibly attributable to spatial/temporal variations in aperture corrections. These variations can be inferred and corrected by measuring the fraction of stellar light in an annulus between 6'' and 8'' diameter. Key elements of this calibration include: correction of amplifier nonlinearities; distinguishing pixel-area variations and stray light from quantum-efficiency variations in the flat fields; field-dependent color corrections; and the use of an aperture-correction proxy. The DECam response pattern across the 2° field drifts over months by up to ±9 mmag, in a nearly wavelength-independent low-order pattern. Here, we find no fundamental barriers to pushing global photometric calibrations toward mmag accuracy.},
doi = {10.1088/1538-3873/aaa753},
journal = {Publications of the Astronomical Society of the Pacific},
number = 987,
volume = 130,
place = {United States},
year = {2018},
month = {4}
}