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Published January 20, 2012 | Accepted Version + Published
Journal Article Open

Spitzer Infrared Observations and Independent Validation of the Transiting Super-Earth CoRoT-7 b


The detection and characterization of the first transiting super-Earth, CoRoT-7 b, has required an unprecedented effort in terms of telescope time and analysis. Although the star does display a radial-velocity signal at the period of the planet, this has been difficult to disentangle from the intrinsic stellar variability and pinning down the velocity amplitude has been very challenging. As a result, the precise value of the mass of the planet—and even the extent to which it can be considered to be confirmed—has been debated in the recent literature, with six mass measurements published so far based on the same spectroscopic observations, ranging from about 2 to 8 Earth masses. Here we report on an independent validation of the planet discovery using one of the fundamental properties of a transit signal: its achromaticity. We observed four transits of CoRoT-7 b at 4.5 μm and 8.0 μm with the Infrared Array Camera (IRAC) on board the Spitzer Space Telescope in order to determine whether the depth of the transit signal in the near-infrared is consistent with that observed in the CoRoT bandpass, as expected for a planet. We detected the transit and found an average depth of 0.426 ± 0.115 mmag at 4.5 μm, which is in good agreement with the depth of 0.350 ± 0.011 mmag (ignoring limb darkening) found by CoRoT. The observations at 8.0 μm did not yield a significant detection. The 4.5 μm observations place important constraints on the kinds of astrophysical false positives that could mimic the signal. Combining this with additional constraints reported earlier, we performed an exhaustive exploration of possible blend scenarios for CoRoT-7 b using the BLENDER technique. We are able to rule out the vast majority of false positives, and the remaining ones are found to be much less likely than a true transiting planet. We thus validate CoRoT-7 b as a bona fide planet with a very high degree of confidence, independently of any radial-velocity information. Our Spitzer observations have additionally allowed us to significantly improve the ephemeris of the planet, so that future transits should be recoverable well into the next decade. In its warm phase Spitzer is expected to be an essential tool for the validation, along the lines of the present analysis, of transiting planet candidates with shallow signals from CoRoT as well as from the Kepler mission, including potentially rocky planets in the habitable zones of their parent stars.

Additional Information

© 2012 American Astronomical Society. Received 2011 July 18; accepted 2011 October 24; published 2011 December 29. We are grateful to the anonymous referee for many very helpful comments and suggestions. 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 contract to NASA. Support for this work was provided by NASA through an award issued by JPL/Caltech. This research has made use of the facilities at the NASA Advanced Supercomputing Division (NASA Ames Research Center).

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Published - 0004-637X_745_1_81.pdf

Accepted Version - 1110.5336.pdf


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