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Title: Photometric Characterization of the Dark Energy Camera

Journal Article · · Publications of the Astronomical Society of the Pacific
 [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)
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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.

Research Organization:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Organization:
USDOE
Grant/Contract Number:
AC02-76SF00515; SC0007901; AST-1615555
OSTI ID:
1434675
Journal Information:
Publications of the Astronomical Society of the Pacific, Vol. 130, Issue 987; ISSN 0004-6280
Publisher:
Astronomical Society of the PacificCopyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 11 works
Citation information provided by
Web of Science

Figures / Tables (11)

Table 1(p. 19)table Table 1
Fig. 1(p. 21)figure Fig. 1
Fig. 2(p. 23)figure Fig. 2
Fig. 3(p. 24)figure Fig. 3
Fig. 4(p. 26)figure Fig. 4
griz, again with a few nights and a few stray exposures of higher level. The third row plots the deviation of the exposure zeropoint shift from the atmospheric secant law for that night. The crosses give the initial values, which are 2{5 mmag RMS, but when the aperture correction of Section 4.3 is applied, the RMS zeropoint variation is reduced to ≈ 1 mmag. The fourth row shows the aperture correction proxy At, the difference between 8"and 6" aperture magnitudes. The fifth row plots the half-light diameter D50 of the PSF, which is seen to be less than fully predictive of At or the zeropoint shifts." data-ostiid="1434675">
Fig. 5(p. 28)figure Fig. 5
Fig. 6(p. 29)figure Fig. 6
Table 2(p. 29)table Table 2
Table 3(p. 30)table Table 3
Fig. 7(p. 33)figure Fig. 7
Fig. 8(p. 34)figure Fig. 8

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Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
instrumentation: detectors
methods: data analysis
techniques: photometric