KEYWORDS: Iterated function systems, Sensors, Photons, James Webb Space Telescope, Telescopes, Instrument modeling, Point spread functions, Calibration, Near infrared spectroscopy
To achieve its ambitious scientific goals, the Near-Infrared Spectrograph, NIRSpec, on board the Webb Space Telescope, needs to meet very demanding throughput requirements, here quantified in terms of photon-conversion efficiency (PCE). During the calibration activities performed for the instrument commissioning, we have obtained the first in-flight measurements of its PCE and also updated the modeling of the light losses occurring in the NIRSpec slit devices. The measured PCE of NIRSpec fixed-slit and multi-object spectroscopy modes overall meets or exceeds the pre-launch model predictions. The results are more contrasted for the integral-field spectroscopy mode, where the differences with the model can reach −20%, above 4 μm, and exceed +30%, below 2 μm. Additionally, thanks to the high quality of the JWST point-spread function, our slit-losses, at the shorter wavelength, are significantly decreased with respect to the pre-flight modeling. These results, combined with the confirmed low noise performance of the detectors, make of NIRSpec an exceptionally sensitive spectrograph.
H. T. Diehl, E. Neilsen, R. Gruendl, T. M. Abbott, S. Allam, O. Alvarez, J. Annis, E. Balbinot, S. Bhargava, K. Bechtol, G. Bernstein, R. Bhatawdekar, S. Bocquet, D. Brout, R. Capasso, R. Cawthon, C. Chang, E. Cook, C. Conselice, J. Cruz, C. D'Andrea, L. da Costa, R. Das, D. DePoy, A. Drlica-Wagner, A. Elliott, S. Everett, J. Frieman, A. Fausti Neto, A. Ferté, I. Friswell, K. Furnell, L. Gelman, D. Gerdes, M. S. Gill, D. Goldstein, D. Gruen, D. Gulledge, S. Hamilton, D. Hollowood, K. Honscheid, D. James, M. Johnson, M. W. Johnson, S. Kent, R. Kessler, G. Khullar, E. Kovacs, A. Kremin, R. Kron, N. Kuropatkin, J. Lasker, A. Lathrop, T. Li, M. Manera, M. March, J. Marshall, M. Medford, F. Menanteau, I. Mohammed, M. Monroy, B. Moraes, E. Morganson, J. Muir, M. Murphy, B. Nord, A. Pace, A. Palmese, Y. Park, F. Paz-Chinchón, M. E. Pereira, D. Petravick, A. Plazas, J. Poh, T. Prochaska, A. Romer, K. Reil, A. Roodman, M. Sako, M. Sauseda, D. Scolnic, L. Secco, I. Sevilla-Noarbe, N. Shipp, J. Smith, M Soares-Santos, B. Soergel, A. Stebbins, K. Story, K. Stringer, F. Tarsitano, B. Thomas, D. Tucker, K. Vivas, A. Walker, M.-Y. Wang, C. Weaverdyck, N. Weaverdyck, W. Wester, C. Wethers, R. Wilkenson, H.-Y Wu, B. Yanny, A. Zenteno, Y. 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 4” (Y4) and “Year 5” (Y5), the survey 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 these two-season's data, a summary of the overall status, and plans for the final survey season.
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