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Warm Spitzer IRAC photometry: dependencies on observing mode and exposure time

Krick, Jessica E. and Lowrance, Patrick J. and Carey, Sean and Surace, Jason A. and Grillmair, Carl J. and Laine, Seppo and Van Dyk, Schuyler D. and Ingalls, James G. and Ashby, Matthew L. N. and Willner, S. P. (2021) Warm Spitzer IRAC photometry: dependencies on observing mode and exposure time. Journal of Astronomical Telescopes, Instruments, and Systems, 7 (3). Art. No. 038006. ISSN 2329-4124. doi:10.1117/1.jatis.7.3.038006.

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We investigate differences in Spitzer/IRAC 3.6 and 4.5  μm photometry that depend on observing strategy. Using archival calibration data, we perform an in-depth examination of the measured flux densities (fluxes) of 10 calibration stars, observed with all the possible observing strategies. We then quantify differences in the measured fluxes as a function of (1) array mode (full or subarray), (2) exposure time, and (3) dithering versus staring observations. We find that the median fluxes measured for sources observed using the full array are 1.6% and 1% lower than those observed with the subarray at [3.6] and [4.5], respectively. In addition, we found a dependence on the exposure time such that for [3.6] observations, the long frame times are measured to be lower than the short frame times by a median value of 3.4% in full array and 2.9% in subarray. For [4.5] observations, the longer frame times are 0.6% and 1.5% in full and subarray, respectively. These very small variations will likely only affect science users who require high-precision photometry from multiple different observing modes. We find no statistically significant difference for fluxes obtained with dithered and staring modes. When considering all stars in the sample, the fractional well depth of the pixel is correlated with the different observed fluxes. We speculate the cause to be a small nonlinearity in the pixels at the lowest well depths where deviations from linearity were previously assumed to be negligible.

Item Type:Article
Related URLs:
URLURL TypeDescription
Krick, Jessica E.0000-0002-2413-5976
Lowrance, Patrick J.0000-0001-8014-0270
Carey, Sean0000-0002-0221-6871
Surace, Jason A.0000-0001-7291-0087
Grillmair, Carl J.0000-0003-4072-169X
Laine, Seppo0000-0003-1250-8314
Van Dyk, Schuyler D.0000-0001-9038-9950
Ingalls, James G.0000-0003-4714-1364
Ashby, Matthew L. N.0000-0002-3993-0745
Willner, S. P.0000-0002-9895-5758
Additional Information:© 2021 The Authors. Published by SPIE under a Creative Commons Attribution 4.0 International License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI. Paper 21056 received May 7, 2021; accepted for publication Sep. 10, 2021; published online Sep. 27, 2021. We thank the anonymous referees for their time and care in providing very useful comments on this manuscript. This work was based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. This research has made use of NASA’s Astrophysics Data System, the NASA/IPAC Infrared Science Archive, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration, and the SIMBAD database, operated at CDS, Strasbourg, France. The acknowledgments were compiled using the Astronomy Acknowledgment Generator.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Subject Keywords:infrared; space telescopes; instrumentation; detectors; photometry
Issue or Number:3
Record Number:CaltechAUTHORS:20211022-224355145
Persistent URL:
Official Citation:Jessica E. Krick, Patrick J. Lowrance, Sean J. Carey, Jason A. Surace, Carl J. Grillmair, Seppo J. Laine, Schuyler D. Van Dyk, James G. Ingalls, Matthew L. N. Ashby, and Steven P. Willner "Warm Spitzer IRAC photometry: dependencies on observing mode and exposure time," Journal of Astronomical Telescopes, Instruments, and Systems 7(3), 038006 (27 September 2021).
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:111621
Deposited By: Tony Diaz
Deposited On:22 Oct 2021 23:58
Last Modified:26 Oct 2021 16:17

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