Modeling Kepler Transit Light Curves as False Positives: Rejection of Blend Scenarios for Kepler-9, and Validation of Kepler-9 d, A Super-earth-size Planet in a Multiple System

January 2011 • 2011ApJ...727...24T

Authors • Torres, Guillermo • Fressin, François • Batalha, Natalie M. • Borucki, William J. • Brown, Timothy M. • Bryson, Stephen T. • Buchhave, Lars A. • Charbonneau, David • Ciardi, David R. • Dunham, Edward W. • Fabrycky, Daniel C. • Ford, Eric B. • Gautier, Thomas N., III • Gilliland, Ronald L. • Holman, Matthew J. • Howell, Steve B. • Isaacson, Howard • Jenkins, Jon M. • Koch, David G. • Latham, David W. • Lissauer, Jack J. • Marcy, Geoffrey W. • Monet, David G. • Prsa, Andrej • Quinn, Samuel N. • Ragozzine, Darin • Rowe, Jason F. • Sasselov, Dimitar D. • Steffen, Jason H. • Welsh, William F.

Abstract • Light curves from the Kepler Mission contain valuable information on the nature of the phenomena producing the transit-like signals. To assist in exploring the possibility that they are due to an astrophysical false positive, we describe a procedure (BLENDER) to model the photometry in terms of a "blend" rather than a planet orbiting a star. A blend may consist of a background or foreground eclipsing binary (or star-planet pair) whose eclipses are attenuated by the light of the candidate and possibly other stars within the photometric aperture. We apply BLENDER to the case of Kepler-9 (KIC 3323887), a target harboring two previously confirmed Saturn-size planets (Kepler-9 b and Kepler-9 c) showing transit timing variations, and an additional shallower signal with a 1.59 day period suggesting the presence of a super-Earth-size planet. Using BLENDER together with constraints from other follow-up observations we are able to rule out all blends for the two deeper signals and provide independent validation of their planetary nature. For the shallower signal, we rule out a large fraction of the false positives that might mimic the transits. The false alarm rate for remaining blends depends in part (and inversely) on the unknown frequency of small-size planets. Based on several realistic estimates of this frequency, we conclude with very high confidence that this small signal is due to a super-Earth-size planet (Kepler-9 d) in a multiple system, rather than a false positive. The radius is determined to be 1.64^+0.19 _-0.14 R _⊕, and current spectroscopic observations are as yet insufficient to establish its mass.

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David Ciardi

Senior Scientist