AN EFFICIENT AUTOMATED VALIDATION PROCEDURE FOR EXOPLANET TRANSIT CANDIDATES

By Timothy Morton. 2012

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Surveys searching for transiting exoplanets have found many more candidates than they have been able to confirm as true planets. This situation is especially acute with the Kepler survey, which has found over 2300 candidates but has to date confirmed only a small fraction of them as planets. I present here a general procedure that can quickly be applied to any planet candidate to calculate its false positive probability. This procedure takes into account the period, depth, duration, and shape of the signal; the colors of the target star; arbitrary spectroscopic or imaging follow-up observations; and informed assumptions about the populations and distributions of field stars and multiple-star properties. Applying these methods to a sample of known Kepler planets, I demonstrate that many signals can be validated with very limited follow-up observations: in most cases with only a spectrum and an adaptive optics image. Additionally, I demonstrate that this procedure can reliably identify false positive signals. Because of the computational efficiency of this analysis, it is feasible to apply it to all Kepler planet candidates in the near future, and it will streamline the follow-up efforts for Kepler and other current and future transit surveys.

Subfields: Astronomy and Astrophysics, Instrumentation, Statistical and Nonlinear Physics

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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, methodology): “We also analyze the false positive probability (FPP) of each system using vespa, a new publicly available, general-purpose implementation of the Morton (2012) procedure to calculate FPPs for transiting planets.”
emcee: The MCMC Hammer (2012, background): “…(Sanders & Fabian 2013; Reis et al. 2013; Weisz et al. 2013; Cieza et al. 2013; Akeret et al. 2012; Huppenkothen et al. 2012; Monnier et al. 2012; Morton 2012; Crossfield et al. 2012; Roškar et al. 2012; Bovy et al. 2012a, 2012b, 2012c; Brown et al. 2012; Brammer et al. 2012; Bussmann et al.…”
EXOPLANET POPULATION INFERENCE AND THE ABUNDANCE OF EARTH ANALOGS FROM NOISY, INCOMPLETE CATALOGS (2014, methodology): “In this mixture model, the false positives would be represented using prior distributions similar to those used by Morton (2012) or Fressin et al. (2013).”
FALSE POSITIVE PROBABILITIES FOR ALL KEPLER OBJECTS OF INTEREST: 1284 NEWLY VALIDATED PLANETS AND 428 LIKELY FALSE POSITIVES (2016, methodology): “…object of interest (KOI) in the Q1-Q17 DR24 table, using the publicly available Python module vespa, which implements the procedure introduced in Morton (2012), with improvements in stellar parameter modeling and the inclusion of new “double-period” false positive scenarios and artificial…”
WASP-47: A HOT JUPITER SYSTEM WITH TWO ADDITIONAL PLANETS DISCOVERED BY K2 (2015, methodology): “We do this using vespa (Morton 2015), an implementation of the procedure de- 8 Tables available at https://github.com/jxcbecker/Data/tree/main/WASP-47 scribed in Morton (2012).”
VALIDATION OF KEPLER'S MULTIPLE PLANET CANDIDATES. II. REFINED STATISTICAL FRAMEWORK AND DESCRIPTIONS OF SYSTEMS OF SPECIAL INTEREST (2014, methodology): “…that aim to validate planet candidates statistically (e.g., BLENDER; Torres et al. 2011; Fressin et al. 2011, and the methods developed by Morton 2012) require as input the base rates of the various astrophysical objects being considered, e.g., abundances of planets versus binary stars.”
Identifying Exoplanets with Deep Learning: A Five-planet Resonant Chain around Kepler-80 and an Eighth Planet around Kepler-90 (2017, methodology): “We performed this calculation using vespa (Morton 2015), an open source code library that implements the methodology described by Morton (2012) and Morton et al. (2016).”
THE FALSE POSITIVE RATE OF KEPLER AND THE OCCURRENCE OF PLANETS (2013, methodology): “We point out that Morton (2012) recently published an automated validation procedure for exoplanet transit candidates based on a similar approach as the MJ11 work, with the improvement that it now considers background stars transited by planets as an additional source of potential blends (item #2…”
They are small worlds after all: revised properties of Kepler M dwarf stars and their planets (2015, background): “Comparison with the astrophysical FP estimates (Morton 2012; Swift et al. 2015) suggests this accounts for less than 3% of systems.”
PLANETARY CANDIDATES FROM THE FIRST YEAR OF THE K2 MISSION (2015, background): “…has been highly successful, finding thousands of planetary candidates (Borucki et al. 2011; Mullally et al. 2015), the majority of which are likely genuine transiting exoplanets (Morton & Johnson 2011; Morton 2012a; Fressin et al. 2013; Lissauer et al. 2012; Rowe et al. 2014; Santerne et al. 2015).”
TERRESTRIAL PLANET OCCURRENCE RATES FOR THE KEPLER GK DWARF SAMPLE (2015, methodology): “Following the process outlined in Morton (2012), a preliminary astrophysical false positive analysis was completed for 108 (70”
SOPHIE velocimetry of Kepler transit candidates XVII. The physical properties of giant exoplanets within 400 days of period (2015, background): “Since those V-shaped candidates actually are in the catalogs, this scenario of false positive should be considered, as it is done in Morton (2012).”
DISCOVERY AND VALIDATION OF Kepler-452b: A 1.6 R⨁ SUPER EARTH EXOPLANET IN THE HABITABLE ZONE OF A G2 STAR (2015, methodology): “In this paper, we apply the BLENDER analysis technique (see Section 9) to validate the planetary nature of Kepler-452b , but note that similar approaches have been developed by others and are in use in transit surveys (see, e.g. Morton 2012; Barclay et al. 2013; Dı́az et al. 2014).”
LOW FALSE POSITIVE RATE OF KEPLER CANDIDATES ESTIMATED FROM A COMBINATION OF SPITZER AND FOLLOW-UP OBSERVATIONS (2015, methodology): “Other approaches use generic arguments about the Kepler signals to in- fer the overall Kepler FPR (e.g., Morton & Johnson 2011; Morton 2012; Fressin et al. 2013).”
CHARACTERIZING THE COOL KOIs. IV. KEPLER-32 AS A PROTOTYPE FOR THE FORMATION OF COMPACT PLANETARY SYSTEMS THROUGHOUT THE GALAXY (2012, methodology): “…calculate the relative probabilities of astrophysical false positive and bona fide transiting planet scenarios, we follow the methodology of Morton (2012), which compares the observed transit shapes to those of simulated false positive populations, subject to the available observational…”
THE RADIUS DISTRIBUTION OF PLANETS AROUND COOL STARS (2013, methodology): “…photometrically characterized by Dressing & Charbonneau (2013), incorporating their individually calculated false positive probabilities following Morton (2012) as well as new MCMC fits for planet radii (Swift et al., in prep), we find that the planet distribution continues to rise…”
The California-Kepler Survey. I. High-resolution Spectroscopy of 1305 Stars Hosting Kepler Transiting Planets (2017, background): “Statistical considerations of false positive scenarios suggest that false positives account for ∼10% of all the planet candidates (Morton & Johnson 2011; Morton 2012; Fressin et al. 2013).”