The Dark Energy Spectroscopic Instrument (DESI) is an ongoing spectroscopic survey to measure the dark energy equation of state to unprecedented precision. We describe the DESI Sky Continuum Monitor System, which tracks the night sky brightness as part of a system that dynamically adjusts the spectroscopic exposure time to produce more uniform data quality and to maximize observing efficiency. The DESI dynamic exposure time calculator (ETC) will combine sky brightness measurements from the Sky Monitor with data from the guider system to calculate the exposure time to achieve uniform signal-to-noise ratio (SNR) in the spectra under various observing conditions. The DESI design includes 20 sky fibers, and these are split between two identical Sky Monitor units to provide redundancy. Each Sky Monitor unit uses an SBIG STXL-6303e CCD camera and supports an eight-position filter wheel. Both units have been completed and delivered to the Mayall Telescope at the Kitt Peak National Observatory. Commissioning results show that the Sky Monitor delivers the required performance necessary for the ETC.
We describe the design of the Commissioning Instrument for the Dark Energy Spectroscopic Instrument (DESI). DESI will obtain spectra over a 3 degree field of view using the 4-meter Mayall Telescope at Kitt Peak, AZ. In order to achieve the required image quality over this field of view, a new optical corrector is being installed at the Mayall Telescope. The Commissioning Instrument is designed to characterize the image quality of the new optical system. The Commissioning Instrument has five commercial cameras; one at the center of the focal surface and four near the periphery of the field and at the cardinal directions. There are also 22 illuminated fiducials, distributed throughout the focal surface, that will be used to test the system that will map between the DESI fiber positioners and celestial coordinates. We describe how the commissioning instrument will perform commissioning tasks for the DESI project and thereby eliminate risks.
The Dark Energy Spectroscopic Instrument (DESI) is under construction to measure the expansion history of the Universe using the Baryon Acoustic Oscillation technique. The spectra of 35 million galaxies and quasars over 14000 sq deg will be measured during the life of the experiment. A new prime focus corrector for the KPNO Mayall telescope will deliver light to 5000 fiber optic positioners. The fibers in turn feed ten broad-band spectrographs. We will describe the methods and results for the commissioning instrument metrology program. The primary goals of this program are to calculate the transformations and further develop the systems that will place fibers within 5μm RMS of the target positions. We will use the commissioning instrument metrology program to measure the absolute three axis Cartesian coordinates of the five CCDs and 22 illuminated fiducials on the commissioning instrument.
H. T. Diehl, E. Neilsen, R. Gruendl, B. Yanny, T. M. Abbott, J. Aleksić, S. Allam, J. Annis, E. Balbinot, M. Baumer, L. Beaufore, K. Bechtol, G. Bernstein, S. Birrer, C. Bonnett, D. Brout, C. Bruderer, E. Buckley-Geer, D. Capozzi, A. Carnero Rosell, F. Castander, R. Cawthon, C. Chang, L. Clerkin, R. Covarrubias, C. Cuhna, C. D'Andrea, L. da Costa, R. Das, C. Davis, J. Dietrich, A. Drlica-Wagner, A. Elliott, T. Eifler, J. Etherington, B. Flaugher, J. Frieman, A. Fausti Neto, M. Fernández, C. Furlanetto, D. Gangkofner, D. Gerdes, D. Goldstein, K. Grabowski, R. Gupta, S. Hamilton, H. Head, J. Helsby, D. Hollowood, K. Honscheid, D. James, M. Johnson, S. Jouvel, T. Kacprzac, S. Kent, R. Kessler, A. Kim, E. Krause, C. Krawiec, A. Kremin, R. Kron, S. Kuhlmann, N. Kuropatkin, O. Lahav, J. Lasker, T. Li, E. Luque, N. Maccrann, M. March, J. Marshall, N. Mondrik, E. Morganson, D. Mudd, A. Nadolski, P. Nugent, P. Melchior, F. Menanteau, D. Nagasawa, B. Nord, R. Ogando, L. Old, A. Palmese, D. Petravick, A. Plazas, A. Pujol, A. Queiroz, K. Reil, A. Romer, R. Rosenfeld, A. Roodman, P. Rooney, M. Sako, A. Salvador, C. Sánchez, E. Sánchez Álvaro, B. Santiago, A. Schooneveld, M. Schubnell, E. Sheldon, A. Smith, R. Smith, M. Soares-Santos, F. Sobreira, M. Soumagnac, H. Spinka, S. Tie, D. Tucker, V. Vikram, K. Vivas, A. Walker, W. Wester, M. Wiesner, H. Wilcox, P. Williams, A. Zenteno, Y. Zhang, Z. Zhang
The Dark Energy Survey (DES) is an operating optical survey aimed at understanding the accelerating expansion of the universe using four complementary methods: weak gravitational lensing, galaxy cluster counts, baryon acoustic oscillations, and Type Ia supernovae. To perform the 5000 sq-degree wide field and 30 sq-degree supernova surveys, the DES Collaboration built the Dark Energy Camera (DECam), a 3 square-degree, 570-Megapixel CCD camera that was installed at the prime focus of the Blanco 4-meter telescope at the Cerro Tololo Inter-American Observatory (CTIO). DES has completed its third observing season out of a nominal five. This paper describes DES “Year 1” (Y1) to “Year 3” (Y3), the strategy, an outline of the survey operations procedures, the efficiency of operations and the causes of lost observing time. It provides details about the quality of the first three season's data, and describes how we are adjusting the survey strategy in the face of the El Niño Southern Oscillation.
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