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

Abstract

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 - have 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 with Spitzer, 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 {\pm} 0.115 mmag at 4.5 μm, which is in good agreement with the depth of 0.350 {\pm} 0.011 mmag found by CoRoT. These 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 blends 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.

Accepted by ApJ

References in corpus (10)

• Detection of Thermal Emission from an Extrasolar Planet
• The Occurrence and Mass Distribution of Close-in Super-Earths, Neptunes, and Jupiters
• The effect of red noise on planetary transit detection
• KEPLER's First Rocky Planet: Kepler-10b
• The Broadband Infrared Emission Spectrum of the Exoplanet HD 189733b
• Modeling Kepler transit light curves as false positives: Rejection of blend scenarios for Kepler-9, and validation of Kepler-9d, a super-Earth-size planet in a multiple system
• On the Mass of CoRoT-7b
• A Sensitive Search for Variability in Late L Dwarfs: The Quest for Weather
• Kepler-10c, a 2.2-Earth radius transiting planet in a multiple system
• The Transit Light Curve (TLC) Project. II. Two Transits of the Exoplanet OGLE-TR-111b

Cited by in corpus (10)

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• 3.6 and 4.5 Micron Phase Curves and Evidence for Non-Equilibrium Chemistry in the Atmosphere of Extrasolar Planet HD 189733b
• Two Earth-sized planets orbiting Kepler-20
• Kepler-20: A Sun-like Star with Three Sub-Neptune Exoplanets and Two Earth-size Candidates
• Kepler-68: Three Planets, One With a Density Between That of Earth and Ice Giants
• CoRoT: harvest of the exoplanet program
• The contribution of secondary eclipses as astrophysical false positives to exoplanet transit surveys
• A low-mass sub-Neptune planet transiting the bright active star HD 73344
• Search for Exoplanetary Transits in the Galactic Bulge