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      A Technique for Extracting Highly Precise Photometry for the Two-Wheeled Kepler Mission

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          Abstract

          The original Kepler mission achieved high photometric precision thanks to ultra-stable pointing enabled by use of four reaction wheels. The loss of two of these reaction wheels reduced the telescope's ability to point precisely for extended periods of time, and as a result, the photometric precision has suffered. We present a technique for generating photometric light curves from pixel-level data obtained with the two-wheeled extended Kepler mission, K2. Our photometric technique accounts for the non-uniform pixel response function of the Kepler detectors by correlating flux measurements with the spacecraft's pointing and removing the dependence. When we apply our technique to the ensemble of stars observed during the Kepler Two-Wheel Concept Engineering Test, we find improvements over raw K2 photometry by factors of 2-5, with noise properties qualitatively similar to Kepler targets at the same magnitudes. We find evidence that the improvement in photometric precision depends on each target's position in the Kepler field of view, with worst precision near the edges of the field. Overall, this technique restores the median attainable photometric precision to within a factor of two of the original Kepler photometric precision for targets ranging from 10\(^{th}\) to 15\(^{th}\) magnitude in the Kepler bandpass, peaking with a median precision within 35% that of Kepler for stars between 12\(^{th}\) and 13\(^{th}\) magnitude in the Kepler bandpass.

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          Author and article information

          Journal
          17 August 2014
          Article
          10.1086/678764
          1408.3853
          e1d52d9a-7a37-46f7-a464-77efb42164b6

          http://arxiv.org/licenses/nonexclusive-distrib/1.0/

          History
          Custom metadata
          PASP Vol. 126, No. 944 (October 2014), pp. 948-958
          11 pages, 8 figures. Submitted to PASP and revised based on reviewer suggestions. All processed K2 engineering data is made available to the community at http://www.cfa.harvard.edu/~avanderb/k2.html
          astro-ph.IM astro-ph.EP astro-ph.SR

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