A calibration of NICMOS Camera 2 for low count rates
- Department of Physics, Florida State University, Tallahassee, FL 32306 (United States)
- E.O. Lawrence Berkeley National Lab, 1 Cyclotron Road, Berkeley, CA 94720 (United States)
- The Oskar Klein Centre, Department of Physics, AlbaNova, Stockholm University, SE-106 91 Stockholm (Sweden)
- Department of Physics and Astronomy, University of Utah, 115 S 1400 E, Salt Lake City, UT 84112 (United States)
- Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)
- Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871 (China)
- Santa Cruz Institute for Particle Physics, University of California, Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 (United States)
- Department of Astronomy and Astrophysics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637 (United States)
- Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, D-14482, Potsdam (Germany)
- Department of Physics, University of California Berkeley, Berkeley, CA 94720 (United States)
- Australian Astronomical Observatory, P.O. Box 296, Epping, NSW 1710 (Australia)
- Department of Physics, Stanford University, 450 Serra Mall, Stanford, CA 94305 (United States)
- Google, Pittsburgh, PA (United States)
NICMOS 2 observations are crucial for constraining distances to most of the existing sample of z>1 SNe Ia. Unlike conventional calibration programs, these observations involve long exposure times and low count rates. Reciprocity failure is known to exist in HgCdTe devices and a correction for this effect has already been implemented for high and medium count rates. However, observations at faint count rates rely on extrapolations. Here instead, we provide a new zero-point calibration directly applicable to faint sources. This is obtained via inter-calibration of NIC2 F110W/F160W with the Wide Field Camera 3 (WFC3) in the low count-rate regime using z∼1 elliptical galaxies as tertiary calibrators. These objects have relatively simple near-IR spectral energy distributions, uniform colors, and their extended nature gives a superior signal-to-noise ratio at the same count rate than would stars. The use of extended objects also allows greater tolerances on point-spread function profiles. We find space telescope magnitude zero points (after the installation of the NICMOS cooling system, NCS) of 25.296 ±0.022 for F110W and 25.803 ±0.023 for F160W, both in agreement with the calibration extrapolated from count rates ≳1000 times larger (25.262 and 25.799). Before the installation of the NCS, we find 24.843 ±0.025 for F110W and 25.498 ±0.021 for F160W, also in agreement with the high-count-rate calibration (24.815 and 25.470). We also check the standard bandpasses of WFC3 and NICMOS 2 using a range of stars and galaxies at different colors and find mild tension for WFC3, limiting the accuracy of the zero points. To avoid human bias, our cross-calibration was “blinded” in that the fitted zero-point differences were hidden until the analysis was finalized.
- OSTI ID:
- 22879482
- Journal Information:
- The Astronomical Journal (Online), Vol. 149, Issue 5; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 1538-3881
- Country of Publication:
- United States
- Language:
- English
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