An asteroseismic view of the radius valley: stripped cores, not born rocky

Eylen, Vincent Van; Agentoft, Camilla; Lundkvist, M.; Kjeldsen, H.; Owen, James E.; Fulton, Benjamin J.; Petigura, Erik A.; Snellen, I. A. G.

doi:10.1093/mnras/sty1783

Cited by 458 publications

(497 citation statements)

References 33 publications

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“…The host star plays an important role in the evolution of its protoplanetary disc for multiple reasons, including determining planetary compositions, affecting the location where grains can condense from the disk, the clearing of the disc via stellar winds (Ercolano & Pascucci 2017), and the timescale for the end of planetesimal accretion. The planet radius valley (Fulton et al 2017;Van Eylen et al 2018;Hsu et al 2019) for planets around FGK-dwarfs is often cited as evidence for the influence of stellar irradiance on planet formation. While photoevaporation (e.g.…”

Section: Comparison To Fgk Occurrence Ratesmentioning

confidence: 99%

Occurrence Rates of Planets Orbiting FGK Stars: Combining Kepler DR25, Gaia DR2, and Bayesian Inference

et al. 2019

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We present robust planet occurrence rates for Kepler planet candidates around M stars for planet radii R p = 0.5 − 4 R ⊕ and orbital periods P = 0.5 − 256 days using the approximate Bayesian computation (ABC) technique. This work incorporates the final Kepler DR25 planet candidate catalog and data products and augment them with updated stellar properties using Gaia DR2 and 2MASS PSC. We analyze a clean sample of 1, 530 Kepler targets that host 89 associated planet candidates. These early M-dwarfs and late K-dwarfs were selected from cross-referenced targets using several photometric quality flags from Gaia DR2 and color-magnitude cuts using 2MASS magnitudes. We identify a habitable zone occurrence rate of f HZ = 0.38 +0.04 −0.05 for planets with 0.75 − 1.5 R ⊕ size. We caution that occurrence rate estimates for Kepler's M stars are sensitive to the choice of prior due to the small sample of target stars and planet candidates. For example, we find an occurrence rate of 8.9 +1.2 −0.9 or 4.8 +0.7 −0.6 planets per M-dwarf (integrating over R p = 0.5 − 4 R ⊕ and P = 0.5 − 256 days) for our two choices of prior. These occurrence rates are greater than those for FGK-dwarf target when compared at the same range of orbital periods, but similar to occurrence rates when computed as a function of equivalent stellar insolation. This suggests that stellar irradiance has a significant and possibly dominant role in planet formation processes regardless of spectral type. Combining our result with recent studies of exoplanet architectures indicates that most, and potentially all, early-M dwarfs harbor planetary systems.

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Section: Comparison To Fgk Occurrence Ratesmentioning

confidence: 99%

Occurrence Rates of Planets Orbiting FGK Stars: Combining Kepler DR25, Gaia DR2, and Bayesian Inference

et al. 2019

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“…They argued that the underlying astrophysical effect could be photoevaporation, whereby stellar incident flux strips a planet's H/He atmosphere if the atmosphere is not thick enough, leaving a population of stripped, rocky planets and an untouched population of larger, gaseous mini-Neptunes (Owen & Wu 2013;Lopez & Rice 2016;Owen & Wu 2017;Van Eylen et al 2017). As an alternative hypothesis, they also suggested that gas accretion could be delayed during planet formation until the protoplanetary disk is already gas poor, creating a population of small, rocky planets (Lee et al 2014;Lee & Chiang 2016).…”

Section: The Planet Radius Distributionmentioning

confidence: 99%

275 Candidates and 149 Validated Planets Orbiting Bright Stars in K2 Campaigns 0–10

et al. 2018

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Since 2014, NASA's K2 mission has observed large portions of the ecliptic plane in search of transiting planets and has detected hundreds of planet candidates. With observations planned until at least early 2018, K2 will continue to identify more planet candidates. We present here 275 planet candidates observed during Campaigns 0-10 of the K2 mission that are orbiting stars brighter than 13 mag (in Kepler band) and for which we have obtained highresolution spectra (R = 44,000). These candidates are analyzed using the vespa package in order to calculate their false-positive probabilities (FPP). We find that 149 candidates are validated with an FPP lower than 0.1%, 39 of which were previously only candidates and 56 of which were previously undetected. The processes of data reduction, candidate identification, and statistical validation are described, and the demographics of the candidates and newly validated planets are explored. We show tentative evidence of a gap in the planet radius distribution of our candidate sample. Comparing our sample to the Kepler candidate sample investigated by Fulton et al., we conclude that more planets are required to quantitatively confirm the gap with K2 candidates or validated planets. This work, in addition to increasing the population of validated K2 planets by nearly 50% and providing new targets for follow-up observations, will also serve as a framework for validating candidates from upcoming K2 campaigns and the Transiting Exoplanet Survey Satellite, expected to launch in 2018.

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“…At R < 4 R ⊕ , most confirmed exoplanets are sub-Neptunes: worlds with R = 1.6 − 3.2 R ⊕ and density < 4 g/cc (e.g., Rogers 2015;Wolfgang et al 2016). Sub-Neptunes probably have 10 3 -10 4 -km-deep H 2 -rich atmospheres cloaking rocky cores (e.g., Owen & Wu 2017;Van Eylen et al 2018), at least for orbital period < 100 d. This implies that sub-Neptunes are mostly atmosphere by volume, and mostly silicate by mass ( Fig. 1).…”

Section: Introductionmentioning

confidence: 96%

Atmosphere Origins for Exoplanet Sub-Neptunes

Kite

Fegley

Schaefer

et al. 2020

ApJ

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Planets with 2 R ⊕ < R < 3 R ⊕ and orbital period <100 d are abundant; these sub-Neptune exoplanets are not well understood. For example, Kepler sub-Neptunes are likely to have deep magma oceans in contact with their atmospheres, but little is known about the effect of the magma on the atmosphere. Here we study this effect using a basic model, assuming that volatiles equilibrate with magma at T ∼ 3000 K. For our Fe-Mg-Si-O-H model system, we find that chemical reactions between the magma and the atmosphere and dissolution of volatiles into the magma are both important. Thus, magma matters. For H, most moles go into the magma, so the mass target for both H 2 accretion and H 2 loss models is weightier than is usually assumed. The known span of magma oxidation states can produce sub-Neptunes that have identical radius but with total volatile masses varying by 20-fold. Thus, planet radius is a proxy for atmospheric composition but not for total volatile content. This redox diversity degeneracy can be broken by measurements of atmosphere mean molecular weight. We emphasise H 2 supply by nebula gas, but also consider solid-derived H 2 O. We find that adding H 2 O to Fe probably cannot make enough H 2 to explain sub-Neptune radii because >10 3 -km thick outgassed atmospheres have high mean molecular weight. The hypothesis of magma-atmosphere equilibration links observables such as atmosphere H 2 O/H 2 ratio to magma FeO content and planet formation processes. Our model's accuracy is limited by the lack of experiments (lab and/or numerical) that are specific to sub-Neptunes; we advocate for such experiments.

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An asteroseismic view of the radius valley: stripped cores, not born rocky

Cited by 458 publications

References 33 publications

Occurrence Rates of Planets Orbiting FGK Stars: Combining Kepler DR25, Gaia DR2, and Bayesian Inference

Occurrence Rates of Planets Orbiting FGK Stars: Combining Kepler DR25, Gaia DR2, and Bayesian Inference

275 Candidates and 149 Validated Planets Orbiting Bright Stars in K2 Campaigns 0–10

Atmosphere Origins for Exoplanet Sub-Neptunes

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