ON THE LOW FALSE POSITIVE PROBABILITIES OF KEPLER PLANET CANDIDATES

By Timothy Morton, J. Johnson. 2011

210 citations recorded by the source corpus.

We present a framework to conservatively estimate the probability that any particular planet-like transit signal observed by the Kepler mission is in fact a planet, prior to any ground-based follow-up efforts. We use Monte Carlo methods based on stellar population synthesis and Galactic structure models, and report false positive probabilities (FPPs) for every Kepler Object of Interest, assuming a 20% intrinsic occurrence rate of close-in planets in the radius range 0.5 R⊕ < Rp < 20 R⊕. Nearly 90% of the 1235 candidates have FPP <10%, and over half have FPP <5%. This probability varies with the magnitude and Galactic latitude of the target star, and with the depth of the transit signal—deeper signals generally have higher FPPs than shallower signals. We establish that a single deep high-resolution image will be an effective follow-up tool for the shallowest (Earth-sized) transits, providing the quickest route toward probabilistically validating the smallest candidates by potentially decreasing the FPP of an Earth-sized transit around a faint star from >10% to <1%. Since Kepler has detected many more planetary signals than can be positively confirmed with ground-based follow-up efforts in the near term, these calculations will be crucial to using the ensemble of Kepler data to determine population characteristics of planetary systems. We also describe how our analysis complements the Kepler team's more detailed BLENDER false positive analysis for planet validation.

Subfields: Astronomy and Astrophysics, Instrumentation

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In Astronomy and Astrophysics

1. D. Charbonneau
2. Timothy Morton
3. Jon Fortney
4. J. Johnson
5. J. Winn
6. G. Marcy
7. Andrew W. Howard
8. J. Owen

In Instrumentation

1. D. Charbonneau
2. Timothy Morton
3. Jon Fortney
4. J. Winn
5. J. Owen
6. J. Southworth
7. J. Johnson
8. Andrew W. Howard

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).”
• A SYSTEMATIC SEARCH FOR TRANSITING PLANETS IN THE K2 DATA (2015, background): “Despite this large fraction of astrophysical false positives in ground-based surveys, the primary Kepler Mission saw a much lower false positive rate of only 5-10% (Morton & Johnson 2011; Fressin et al. 2013), primarily due to three major factors.”
• CHARACTERIZING THE COOL KOIs. IV. KEPLER-32 AS A PROTOTYPE FOR THE FORMATION OF COMPACT PLANETARY SYSTEMS THROUGHOUT THE GALAXY (2012, background): “The probabilities for Kepler planet candidates to be astrophysical false positives, such as blended stellar eclipsing binaries, are generally low (Morton & Johnson 2011), and may even be negligible in multiply transiting systems (Lissauer et al. 2012).”
• One of the closest exoplanet pairs to the 3:2 mean motion resonance: K2-19b and c (2015, background): “A background source of false positives can only mimic the transit depths of the planets if its magnitude is within a range ∆m defined as (Morton & Johnson 2011): ∆m = 2.5 log10 ( δtr δbg ) , (8) where δtr and δbg are the depths of the transit, as measured in the light curve, and the depth on the…”
• FALSE POSITIVE PROBABILITIES FOR ALL KEPLER OBJECTS OF INTEREST: 1284 NEWLY VALIDATED PLANETS AND 428 LIKELY FALSE POSITIVES (2016, methodology): “The false positive rates calculated in Désert et al. (2015) are also based on probabilistic arguments very similar to Morton & Johnson (2011) and thus are not quite candidates for “ground-truth” comparison, but the lack of transit chromaticity and the agreements between these two independent…”
• ALMOST ALL OF KEPLER'S MULTIPLE-PLANET CANDIDATES ARE PLANETS (2012, methodology): “Some candidates were not vetted as extensively as assumed by Morton & Johnson (2011), and other candidates did not pass one of the cleanness tests but still remain viable, if somewhat more suspect, planetary candidates (e.g., grazing planetary transits, as well as grazing stellar eclipses, produce…”
• TESTING IN SITU ASSEMBLY WITH THE KEPLER PLANET CANDIDATE SAMPLE (2013, background): “%) than originally estimated (Morton & Johnson 2011), but it is not clear that the same false positive rate will apply to systems with smaller eclipses.”
• CHARACTERISTICS OF PLANETARY CANDIDATES OBSERVED BY KEPLER. II. ANALYSIS OF THE FIRST FOUR MONTHS OF DATA (2011, background): “A careful assessment of false positive scenarios, especially background and gravitationally bound eclipsing binaries and planets, suggests that 90%–95% of the Kepler planet candidates are indeed true planets (Morton & Johnson 2011).”
• THE OCCURRENCE OF POTENTIALLY HABITABLE PLANETS ORBITING M DWARFS ESTIMATED FROM THE FULL KEPLER DATASET AND AN EMPIRICAL MEASUREMENT OF THE DETECTION SENSITIVITY (2015, background): “Due to the low false positive rate expected for the Kepler planet candidate sample (Morton & Johnson 2011), the Howard et al. (2012) and Youdin (2011) analyses assumed that all of the candidates were bona fide transiting planets.”
• KEPLER PLANETS: A TALE OF EVAPORATION (2013, background): “Most of the KOIs have not been confirmed as planets, and there is a certain, but low, percentage of false positives (Morton & Johnson 2011).”
• VALIDATION OF KEPLER'S MULTIPLE PLANET CANDIDATES. II. REFINED STATISTICAL FRAMEWORK AND DESCRIPTIONS OF SYSTEMS OF SPECIAL INTEREST (2014, background): “The a priori likelihood of a chance-alignment blend for a given target depends on the population of background stars, which is more than an order of magnitude larger at the lowest galactic latitudes observed by Kepler than at the highest latitudes (Morton & Johnson 2011).”
• EXOPLANET POPULATION INFERENCE AND THE ABUNDANCE OF EARTH ANALOGS FROM NOISY, INCOMPLETE CATALOGS (2014, background): “While many of these candidates have not been confirmed as bona fide planets, there is evidence that the false positive rate is low (Morton & Johnson 2011; Fressin et al. 2013), enabling conclusions about the population of planets based on the catalog of candidates.”
• VALIDATION OF KEPLER'S MULTIPLE PLANET CANDIDATES. III. LIGHT CURVE ANALYSIS AND ANNOUNCEMENT OF HUNDREDS OF NEW MULTI-PLANET SYSTEMS (2014, background): “The remaining 2530 systems are composed of primarily exoplanetary systems with an expected FP rate of approximately 10% due to photometric blends (Morton & Johnson 2011; Fressin et al. 2013; Santerne et al. 2013).”
• THE OCCURRENCE RATE OF SMALL PLANETS AROUND SMALL STARS (2013, background): “…but we count this system as a quadruple planet system because KOI 952.05 was not included in the February 2012 planet candidate list. ies have demonstrated that the false positive rate is low for the planet candidates identified by the Kepler team (Morton & Johnson 2011; Fressin et al. 2013).”
• A FIRST COMPARISON OF KEPLER PLANET CANDIDATES IN SINGLE AND MULTIPLE SYSTEMS (2011, background): “Nevertheless, in general it must be true that false positives due to chance alignments must be much less common among multiples than singles, and even for singles the rate of residual false positives among the vetted candidates may be as low as 5 or 10 percent (Morton & Johnson 2011).”
• SOPHIE velocimetry of Kepler transit candidates VII. A false-positive rate of 35% for Kepler close-in giant candidates (2012, methodology): “Morton & Johnson (2011) argue that this type of false positive can be effectively weeded out by a detailed analysis of the Kepler photometry alone.”
• LOW FALSE POSITIVE RATE OF KEPLER CANDIDATES ESTIMATED FROM A COMBINATION OF SPITZER AND FOLLOW-UP OBSERVATIONS (2015, methodology): “We now compare our findings to the study of Morton & Johnson (2011).”