Validation of Small Kepler Transiting Planet Candidates in or near the Habitable Zone

Torres, Guillermo; Kane, Stephen R.; Rowe, Jason F.; Batalha, Natalie M.; Henze, Christopher E.; Ciardi, David R.; Barclay, Thomas; Borucki, W. J.; Buchhave, Lars A.; Crepp, Justin R.; Everett, Mark E.; Horch, Elliott; Howard, Andrew W.; Howell, Steve B.; Isaacson, Howard; Jenkins, Jon M.; Latham, David W.; Petigura, Erik A.; Quintana, Elisa V.

doi:10.3847/1538-3881/aa984b

Cited by 51 publications

(10 citation statements)

References 83 publications

(162 reference statements)

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“…While there are a few on-going efforts (e.g., Burke et al 2019), the faintness of the Kepler stars, combined with the large orbital period and transit duration of these candidates, makes it unlikely that all of them can be independently confirmed. Statistical validation, which includes ancillary observational evidence, has been also pursued (e.g., Torres et al 2017) but it cannot be extended to long-period, low signal-to-noise planets (Mullally et al 2018;Burke et al 2019).…”

Section: Discussion and Outlookmentioning

confidence: 99%

The Impact of Stripped Cores on the Frequency of Earth-size Planets in the Habitable Zone

Pascucci

Mulders

Lopez

2019

ApJL

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The frequency of Earth-size planets in the habitable zone of Sun-like stars, hereafter η ⊕ , is a key parameter to evaluate the yield of nearby Earth analogues that can be detected and characterized by future missions. Yet, this value is poorly constrained as there are no reliable exoplanet candidates in the habitable zone of Sun-like stars in the Kepler field. Here, we show that extrapolations relying on the population of small (< 1.8 R ⊕ ) short-period (< 25 days) planets bias η ⊕ to large values. As the radius distribution at short orbital periods is strongly affected by atmospheric loss, we re-evaluate η ⊕ using exoplanets at larger separations. We find that η ⊕ drops considerably, to values of only ∼ 5−10%. Observations of young (< 100 Myr) clusters can probe short-period sub-Neptunes that still retain most of their envelope mass. As such, they can be used to quantify the contamination of sub-Neptunes to the population of Kepler short-period small planets and aid in more reliable estimates of η ⊕ .

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Section: Discussion and Outlookmentioning

confidence: 99%

The Impact of Stripped Cores on the Frequency of Earth-size Planets in the Habitable Zone

Pascucci

Mulders

Lopez

2019

ApJL

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“…Having excluded the only visible neighboring star within the aperture as the source of the transit signal, we then examined the likelihood of a false positive caused by unseen stars. For this, we applied the BLENDER statistical validation technique (Torres et al 2004(Torres et al , 2011b that has been used previously to validate candidates from the Kepler mission (see, e.g., Torres et al 2017;Fressin et al 2012;Borucki et al 2013;Barclay et al 2013;Meibom et al 2013;Kipping et al 2014Kipping et al , 2016Jenkins et al 2015). For full details of the methodology and additional examples of its application, we refer the reader to the first three sources above.…”

Section: False-alarm Probabilitymentioning

confidence: 99%

K2-231 b: A Sub-Neptune Exoplanet Transiting a Solar Twin in Ruprecht 147

Curtis

Vanderburg

Torres

et al. 2018

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We identify a sub-Neptune exoplanet (R p = 2.5 ± 0.2 R ⊕ ) transiting a solar twin in the Ruprecht 147 star cluster (3 Gyr, 300 pc, [Fe/H] = +0.1 dex). The ∼81 day light-curve for EPIC 219800881 (V = 12.71) from K2 Campaign 7 shows six transits with a period of 13.84 days, a depth of ∼0.06%, and a Based on our analysis of high-resolution MIKE spectra, broadband optical and NIR photometry, the cluster parallax and interstellar reddening, and isochrone models from PARSEC, Dartmouth, and MIST, we estimate the following properties for the host star: M = 1.01 ± 0.03 M , R = 0.95 ± 0.03 R , and T eff = 5695 ± 50 K. This star appears to be single based on our modeling of the photometry, the low radial velocity (RV) variability measured over nearly ten years, and Keck/NIRC2 adaptive optics imaging and aperture-masking interferometry. Applying a probabilistic mass-radius relation, we estimate that the mass of this planet is M p = 7 + 5 − 3 M ⊕ , which would cause an RV semi-amplitude of K = 2 ± 1 m s −1 that may be measurable with existing precise RV facilities. After statistically validating this planet with BLENDER, we now designate it K2-231 b, making it the second substellar object to be discovered in Ruprecht 147 and the first planet; it joins the small but growing ranks of 22 other planets and 3 candidates found in open clusters.

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“…It has generally been accepted in the statistical validation of Kepler candidates from the prime mission (Rowe et al 2014;Morton et al 2016;Torres et al 2017) that adopting SNR>10 for Kepler planet candidates is sufficient to avoid contamination by false alarms. As we have seen, after quantifying an acceptable threshold to avoid false alarms, limiting SNR>10 was helpful guidance.…”

Section: Min Snr For Statistical Confirmationmentioning

confidence: 99%

Re-evaluating Small Long-period Confirmed Planets from Kepler

Burke

Mullally

Thompson

et al. 2019

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We re-examine the statistical confirmation of small long-period Kepler planet candidates in light of recent improvements in our understanding of the occurrence of systematic false alarms in this regime. Using the final Data Release 25 (DR25) Kepler planet candidate catalog statistics, we find that the previously confirmed single planet system Kepler-452b no longer achieves a 99% confidence in the planetary hypothesis and is not considered statistically validated in agreement with the finding of Mullally et al. (2018). For multiple planet systems, we find that the planet prior enhancement for belonging to a multiple planet system is suppressed relative to previous Kepler catalogs, and we identify the multi-planet system member, Kepler-186f, no longer achieves a 99% confidence in the planetary hypothesis. Because of the numerous confounding factors in the data analysis process that leads to the detection and characterization of a signal, it is difficult to determine whether any one planetary candidate achieves a strict criterion for confirmation relative to systematic false alarms. For instance, when taking into account a simplified model of processing variations, the additional single planet systems Kepler-443b, Kepler-441b, Kepler-1633b, Kepler-1178b, and Kepler-1653b have a nonnegligible probability of falling below a 99% confidence in the planetary hypothesis. The systematic false alarm hypothesis must be taken into account when employing statistical validation techniques in order to confirm planet candidates that approach the detection threshold of a survey. We encourage those performing transit searches of K2, TESS, and other similar data sets to quantify their systematic false alarms rates. Alternatively, independent photometric detection of the transit signal or radial velocity measurements can eliminate the false alarm hypothesis.

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Validation of Small Kepler Transiting Planet Candidates in or near the Habitable Zone

Cited by 51 publications

References 83 publications

The Impact of Stripped Cores on the Frequency of Earth-size Planets in the Habitable Zone

The Impact of Stripped Cores on the Frequency of Earth-size Planets in the Habitable Zone

K2-231 b: A Sub-Neptune Exoplanet Transiting a Solar Twin in Ruprecht 147

Re-evaluating Small Long-period Confirmed Planets from Kepler

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