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Intra-pixel gain variations and high-precision photometry with the Infrared Array Camera (IRAC)

Ingalls, James G. and Krick, Jessica E. and Carey, Sean J. and Laine, Seppo and Surace, Jason A. and Glaccum, William J. and Grillmair, Carl C. and Lowrance, Patrick J. (2012) Intra-pixel gain variations and high-precision photometry with the Infrared Array Camera (IRAC). In: Space telescopes and instrumentation 2012: optical, infrared, and millimeter wave. Proceedings of SPIE. No.8442. International Society for Optical Engineering , Bellingham, WA, Art. No. 84421Y. ISBN 978-0-8194-9143-5.

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The Infrared Array Camera (IRAC) on the Spitzer Space Telescope has been used to measure < 10^(-4) temporal variations in point sources (such as transiting extrasolar planets) at 3.6 and 4.5 μm. Due to the under-sampled nature of the PSF, the warm IRAC arrays show variations of as much as 8% in sensitivity as the center of the PSF moves across a pixel due to normal spacecraft pointing wobble and drift. These intra-pixel gain variations are the largest source of correlated noise in IRAC photometry. Usually this effect is removed by fitting a model to the science data themselves (self-calibration), which could result in the removal of astrophysically interesting signals. We describe a new technique for significantly reducing the gain variations and improving photometric precision in a given observation, without using the data to be corrected. This comprises: (1) an adaptive centroiding and repositioning method ("Peak-Up") that uses the Spitzer Pointing Control Reference Sensor (PCRS) to repeatedly position a target to within 0.1 IRAC pixels of an area of minimal gain variation; and (2) the high-precision, high-resolution measurement of the pixel gain structure using non-variable stars. We show that the technique currently allows the reduction of correlated noise by almost an order of magnitude over raw data, which is comparable to the improvement due to self-calibration. We discuss other possible sources of correlated noise, and proposals for reducing their impact on photometric precision.

Item Type:Book Section
Related URLs:
URLURL TypeDescription
Ingalls, James G.0000-0003-4714-1364
Carey, Sean J.0000-0002-0221-6871
Laine, Seppo0000-0003-1250-8314
Surace, Jason A.0000-0001-7291-0087
Grillmair, Carl C.0000-0003-4072-169X
Lowrance, Patrick J.0000-0001-8014-0270
Additional Information:© 2012 SPIE. Published: 22 August 2012. This work is based 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.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Subject Keywords:methods: data analysis; space vehicles: instruments; techniques: photometric; planetary systems; observatories: Spitzer
Series Name:Proceedings of SPIE
Issue or Number:8442
Record Number:CaltechAUTHORS:20121219-090321271
Persistent URL:
Official Citation:James G. Ingalls ; Jessica E. Krick ; Sean J. Carey ; Seppo Laine ; Jason A. Surace ; William J. Glaccum ; Carl C. Grillmair ; Patrick J. Lowrance; Intra-pixel gain variations and high-precision photometry with the Infrared Array Camera (IRAC). Proc. SPIE 8442, Space Telescopes and Instrumentation 2012: Optical, Infrared, and Millimeter Wave, 84421Y (September 21, 2012); doi:10.1117/12.926947.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:36040
Deposited By: Tony Diaz
Deposited On:06 Mar 2013 18:09
Last Modified:04 Nov 2019 21:34

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