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The Dark Energy Camera

B. Flaugher, H. T. Diehl, K. Honscheid, T. M. C. Abbott, O. Alvarez, R. Angstadt, J. T. Annis, M. Antonik, O. Ballester, L. Beaufore, G. M. Bernstein, R. A. Bernstein, B. Bigelow, M. Bonati, D. Boprie, D. Brooks, E. J. Buckley-Geer, J. Campa, L. Cardiel-Sas, F. J. Castander, J. Castilla, H. Cease, J. M. Cela-Ruiz, S. Chappa, E. Chi, C. Cooper, L. N. da Costa, E. Dede, G. Derylo, D. L. DePoy, J. de Vicente, P. Doel, A. Drlica-Wagner, J. Eiting, A. E. Elliott, J. Emes, J. Estrada, A. Fausti Neto, D. A. Finley, R. Flores, J. Frieman, D. Gerdes, M. D. Gladders, B. Gregory, G. R. Gutierrez, J. Hao, S. E. Holland, S. Holm, D. Huffman, C. Jackson, D. J. James, M. Jonas, A. Karcher, I. Karliner, S. Kent, R. Kessler, M. Kozlovsky, R. G. Kron, D. Kubik, K. Kuehn, S. Kuhlmann, K. Kuk, O. Lahav, A. Lathrop, J. Lee, M. E. Levi, P. Lewis, T. S. Li, I. Mandrichenko, J. L. Marshall, G. Martinez, K. W. Merritt, R. Miquel, F. Munoz, E. H. Neilsen, R. C. Nichol, B. Nord, R. Ogando, J. Olsen, N. Palio, K. Patton, J. Peoples, A. A. Plazas, J. Rauch, K. Reil, J. -P. Rheault, N. A. Roe, H. Rogers, A. Roodman, E. Sanchez, V. Scarpine, R. H. Schindler, R. Schmidt, R. Schmitt, M. Schubnell, K. Schultz, P. Schurter, L. Scott, S. Serrano, T. M. Shaw, R. C. Smith, M. Soares-Santos, A. Stefanik, W. Stuermer, E. Suchyta, A. Sypniewski, G. Tarle, J. Thaler, R. Tighe, C. Tran, D. Tucker, A. R. Walker, G. Wang, M. Watson, C. Weaverdyck, W. Wester, R. Woods, B. Yanny

TL;DR

DECam is a 570 MPix, 2.2-degree FoV imager developed for the Dark Energy Survey and mounted at the Blanco telescope. The paper provides a comprehensive technical description of the optical corrector, focal plane detectors, Dewar, front-end electronics, filter/shutter/active optics, instrument control (SISPI), and calibration systems, along with assembly and installation experience. The instrument demonstrates meeting or exceeding wide-field survey requirements, with fast readout, low noise, robust reliability, and extensive calibration capabilities such as DECal, RASICAM, GPSMon, and aTmCam, enabling precise photometry and shape measurements for cosmological probes. The DECam system, including its hexapod-based Active Optics System and a flexible software ecosystem, represents a significant step forward for large-aperture, wide-field astronomical instrumentation and DES science operations.

Abstract

The Dark Energy Camera is a new imager with a 2.2-degree diameter field of view mounted at the prime focus of the Victor M. Blanco 4-meter telescope on Cerro Tololo near La Serena, Chile. The camera was designed and constructed by the Dark Energy Survey Collaboration, and meets or exceeds the stringent requirements designed for the wide-field and supernova surveys for which the collaboration uses it. The camera consists of a five element optical corrector, seven filters, a shutter with a 60 cm aperture, and a CCD focal plane of 250 micron thick fully-depleted CCDs cooled inside a vacuum Dewar. The 570 Mpixel focal plane comprises 62 2kx4k CCDs for imaging and 12 2kx2k CCDs for guiding and focus. The CCDs have 15 microns x15 microns pixels with a plate scale of 0.263 arc sec per pixel. A hexapod system provides state-of-the-art focus and alignment capability. The camera is read out in 20 seconds with 6-9 electrons readout noise. This paper provides a technical description of the camera's engineering, construction, installation, and current status.

The Dark Energy Camera

TL;DR

DECam is a 570 MPix, 2.2-degree FoV imager developed for the Dark Energy Survey and mounted at the Blanco telescope. The paper provides a comprehensive technical description of the optical corrector, focal plane detectors, Dewar, front-end electronics, filter/shutter/active optics, instrument control (SISPI), and calibration systems, along with assembly and installation experience. The instrument demonstrates meeting or exceeding wide-field survey requirements, with fast readout, low noise, robust reliability, and extensive calibration capabilities such as DECal, RASICAM, GPSMon, and aTmCam, enabling precise photometry and shape measurements for cosmological probes. The DECam system, including its hexapod-based Active Optics System and a flexible software ecosystem, represents a significant step forward for large-aperture, wide-field astronomical instrumentation and DES science operations.

Abstract

The Dark Energy Camera is a new imager with a 2.2-degree diameter field of view mounted at the prime focus of the Victor M. Blanco 4-meter telescope on Cerro Tololo near La Serena, Chile. The camera was designed and constructed by the Dark Energy Survey Collaboration, and meets or exceeds the stringent requirements designed for the wide-field and supernova surveys for which the collaboration uses it. The camera consists of a five element optical corrector, seven filters, a shutter with a 60 cm aperture, and a CCD focal plane of 250 micron thick fully-depleted CCDs cooled inside a vacuum Dewar. The 570 Mpixel focal plane comprises 62 2kx4k CCDs for imaging and 12 2kx2k CCDs for guiding and focus. The CCDs have 15 microns x15 microns pixels with a plate scale of 0.263 arc sec per pixel. A hexapod system provides state-of-the-art focus and alignment capability. The camera is read out in 20 seconds with 6-9 electrons readout noise. This paper provides a technical description of the camera's engineering, construction, installation, and current status.

Paper Structure

This paper contains 61 sections, 59 figures, 7 tables.

Table of Contents

  1. Introduction
  2. Optical Corrector
  3. Optical Specifications and Performance Goals
  4. Field of View and Pixel Scale
  5. Image Quality and Wavelength Range
  6. Ghosting and Surface Coatings
  7. Lens Dimensions and the Use of Aspherical Surfaces
  8. Characteristics of the DECam Optical Design
  9. Filters
  10. Barrel
  11. C1 to C4 Lens Cells
  12. C5 Cell and Interface Flange
  13. Alignment and Assembly
  14. Prime Focus Cage
  15. Focal Plane Detectors
  16. ...and 46 more sections

Figures (59)

  • Figure 2: The Dark Energy Camera is mounted at the Prime Focus of the Blanco 4m telescope at CTIO. The primary mirror is just out of the photo, low and to the left. The camera assembly, including the support cage, is approximately 3.6 meters long and is secured to the inner telescope ring. The camera, not including the support cage and counterweights, weighs approximately 4350 kgs.
  • Figure 3: The Dark Energy Camera and Prime Focus Cage. The primary mirror (not shown) is to the left side of the camera. Listing major components starting from the right side of the diagram, the imager vessel is green. The electronics crates are red. The optical elements are supported by the barrel (blue). The filter changer (grey) has the sides removed so that the filters (green) can be seen in the out position. The arms of the hexapod are white. The crown of the 1st corrector element (C1) can be seen at the left side of the barrel. The camera is attached to the cage at the heavy-duty "hexapod ring". The cage is attached to the telescope by the four "fin" structures, which are also shown.
  • Figure 4: The baseline optical design for DECam. The elements, from right to left, are C1, C2, C3, a plano-plano filter (1 of 4 positions is shown), C4, C5 (Dewar window), and the focal plane array. The primary mirror is approximately 8.9 m from the vertex of C1. The total length of the camera from C1 to the focal plane is approximately 1.9 m. The full range of incidence angles on the filters is $0 - 14 ^{\circ}$.
  • Figure 5: The rms image radius as a function of field position. The plots show the image radius for the u- (upper) and g-band (lower). The full y-scale on each plot depends on the filter. For u-band (g-band) that is $50\mu$m ($20\mu$m). The different colors show the wavelengths at which the images were traced within the bandpass; these are listed in the lower left panel of each plot.
  • Figure 6: The rms image radius as a function of field position. The plots show the image radius for the r- (upper) and i-band (lower). The full y-scale on each plot is $10\mu$m. The different colors show the wavelengths at which the images were traced within the bandpass; these are listed in the lower left panel of each plot.
  • ...and 54 more figures