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Repeatability and Accuracy of Exoplanet Eclipse Depths Measured with Post-Cryogenic Spitzer

Ingalls, James G. and Krick, J. E. and Carey, S. J. and Stauffer, John R. and Lowrance, Patrick J. and Grillmair, Carl J. and Buzasi, Derek and Deming, Drake and Diamond-Lowe, Hannah and Evans, Thomas M. and Morello, G. and Stevenson, Kevin B. and Wong, Ian and Capak, Peter and Glaccum, William J. and Laine, Seppo and Surace, Jason and Storrie-Lombardi, Lisa (2016) Repeatability and Accuracy of Exoplanet Eclipse Depths Measured with Post-Cryogenic Spitzer. Astronomical Journal, 152 (2). Art. No. 44. ISSN 1538-3881.

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We examine the repeatability, reliability, and accuracy of differential exoplanet eclipse depth measurements made using the InfraRed Array Camera (IRAC) on the Spitzer Space Telescope during the post-cryogenic mission. We have re-analyzed an existing 4.5 μm data set, consisting of 10 observations of the XO-3b system during secondary eclipse, using seven different techniques for removing correlated noise. We find that, on average, for a given technique, the eclipse depth estimate is repeatable from epoch to epoch to within 156 parts per million (ppm). Most techniques derive eclipse depths that do not vary by more than a factor 3 of the photon noise limit. All methods but one accurately assess their own errors: for these methods, the individual measurement uncertainties are comparable to the scatter in eclipse depths over the 10 epoch sample. To assess the accuracy of the techniques as well as to clarify the difference between instrumental and other sources of measurement error, we have also analyzed a simulated data set of 10 visits to XO-3b, for which the eclipse depth is known. We find that three of the methods (BLISS mapping, Pixel Level Decorrelation, and Independent Component Analysis) obtain results that are within three times the photon limit of the true eclipse depth. When averaged over the 10 epoch ensemble, 5 out of 7 techniques come within 60 ppm of the true value. Spitzer exoplanet data, if obtained following current best practices and reduced using methods such as those described here, can measure repeatable and accurate single eclipse depths, with close to photon-limited results.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Ingalls, James G.0000-0003-4714-1364
Carey, S. J.0000-0002-0221-6871
Stauffer, John R.0000-0003-3595-7382
Lowrance, Patrick J.0000-0001-8014-0270
Grillmair, Carl J.0000-0003-4072-169X
Deming, Drake0000-0001-5727-4094
Evans, Thomas M.0000-0001-5442-1300
Stevenson, Kevin B.0000-0002-7352-7941
Wong, Ian0000-0001-9665-8429
Capak, Peter0000-0003-3578-6843
Laine, Seppo0000-0003-1250-8314
Surace, Jason0000-0001-7291-0087
Storrie-Lombardi, Lisa0000-0002-5987-5210
Additional Information:© 2016 The American Astronomical Society. Received 2016 February 19; revised 2016 May 23; accepted 2016 May 26; published 2016 August 4. We thank the anonymous referee for comments that greatly improved the quality of the paper. We thank Nick Cowan for a thorough reading of an early version of the manuscript and for discussions that helped clarify the conclusions. 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. G.M. received support from ERC project number 617119 (ExoLights). K.S. recognizes support from the Sagan Fellowship Program, supported by NASA and administered by the NASA Exoplanet Science Institute (NExScI). This research has made use of the Exoplanet Orbit Database and the Exoplanet Data Explorer at Facility: Spitzer(IRAC) - Spitzer Space Telescope satellite. Software: IRACSIM (, IDL.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
European Research Council (ERC)617119
Issue or Number:2
Record Number:CaltechAUTHORS:20160805-083752244
Persistent URL:
Official Citation:James G. Ingalls et al 2016 The Astronomical Journal 152 44
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:69461
Deposited By: Ruth Sustaita
Deposited On:05 Aug 2016 16:30
Last Modified:14 Nov 2019 23:44

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