LOW FALSE POSITIVE RATE OF KEPLER CANDIDATES ESTIMATED FROM A COMBINATION OF SPITZER AND FOLLOW-UP OBSERVATIONS

By J. D'esert, D. Charbonneau, G. Torres, F. Fressin, S. Ballard, S. Bryson, H. Knutson, N. Batalha, William J. Borucki, T. Brown and 6 more. 2015

43 citations recorded by the source corpus.

NASA’s Kepler mission has provided several thousand transiting planet candidates during the 4 yr of its nominal mission, yet only a small subset of these candidates have been confirmed as true planets. Therefore, the most fundamental question about these candidates is the fraction of bona fide planets. Estimating the rate of false positives of the overall Kepler sample is necessary to derive the planet occurrence rate. We present the results from two large observational campaigns that were conducted with the Spitzer Space Telescope during the the Kepler mission. These observations are dedicated to estimating the false positive rate (FPR) among the Kepler candidates. We select a sub-sample of 51 candidates, spanning wide ranges in stellar, orbital, and planetary parameter space, and we observe their transits with Spitzer at 4.5 μm. We use these observations to measures the candidate’s transit depths and infrared magnitudes. An authentic planet produces an achromatic transit depth (neglecting the modest effect of limb darkening). Conversely a bandpass-dependent depth alerts us to the potential presence of a blending star that could be the source of the observed eclipse: a false positive scenario. For most of the candidates (85%), the transit depths measured with Kepler are consistent with the transit depths measured with Spitzer as expected for planetary objects, while we find that the most discrepant measurements are due to the presence of unresolved stars that dilute the photometry. The Spitzer constraints on their own yield FPRs between 5% and depending on the Kepler Objects of Interest. By considering the population of the Kepler field stars, and by combining follow-up observations (imaging) when available, we find that the overall FPR of our sample is low. The measured upper limit on the FPR of our sample is 8.8% at a confidence level of 3σ. This observational result, which uses the achromatic property of planetary transit signals that is not investigated by the Kepler observations, provides an independent indication that Kepler’s FPR is low.

Subfields: Astronomy and Astrophysics

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Citations in the corpus

STELLAR AND PLANETARY PROPERTIES OF K2 CAMPAIGN 1 CANDIDATES AND VALIDATION OF 17 PLANETS, INCLUDING A PLANET RECEIVING EARTH-LIKE INSOLATION (2015, background): “The fidelity of this sample is high: most of these candidates are truly planets (Morton & Johnson 2011; Fressin et al. 2013; Désert et al. 2015).”
FALSE POSITIVE PROBABILITIES FOR ALL KEPLER OBJECTS OF INTEREST: 1284 NEWLY VALIDATED PLANETS AND 428 LIKELY FALSE POSITIVES (2016, methodology): “Spitzer photometry The first of these datasets is from Désert et al. (2015), who observe the transits of 50 Kepler candidates with the Spitzer Space Telescope in order to observationally constrain the FP rate.”
TERRESTRIAL PLANET OCCURRENCE RATES FOR THE KEPLER GK DWARF SAMPLE (2015, background): “The astrophysical false positive contamination rates have observationally (Santerne et al. 2012; Désert et al. 2015) and theoretically (Morton & Johnson 2011; Fressin et al. 2013) been shown to increase towards shorter Porb.”
The California-Kepler Survey. I. High-resolution Spectroscopy of 1305 Stars Hosting Kepler Transiting Planets (2017, methodology): “The Spitzer Space Telescope was also used for characterization of Kepler-discovered planets (Désert et al. 2015).”
SOPHIE velocimetry of Kepler transit candidates XVII. The physical properties of giant exoplanets within 400 days of period (2015, methodology): “Recently, Désert et al. (2015) found a false-positive rate as low as 1.3% (upper-limit of 8.8% at 3-σ) based on the Spitzer near-infrared photometry of 51 candidates.”
THE KEPLER FOLLOW-UP OBSERVATION PROGRAM. I. A CATALOG OF COMPANIONS TO KEPLER STARS FROM HIGH-RESOLUTION IMAGING (2016, background): “…positives is a complex process addressed in many publications (Fressin et al. 2013; Coughlin et al. 2014; Seader et al. 2015; Mullally et al. 2015; Desert et al. 2015; McCauliff et al. 2015; Santerne et al. 2016; Morton et al. 2016), with current estimates for false positive rates ranging from ∼…”
SPITZER OBSERVATIONS CONFIRM AND RESCUE THE HABITABLE-ZONE SUPER-EARTH K2-18b FOR FUTURE CHARACTERIZATION (2016, background): “Widely different transit depths at visible and infrared wavelengths could alert us to the potential presence of a blended star that would affect the inferred planetary radius measurement (Stevenson et al. 2014) or even be the source of a false positive scenario (Désert et al. 2015).”