Occurrence rates of planets orbiting M Stars: applying ABC to <i>Kepler</i> DR25, <i>Gaia</i> DR2, and 2MASS data

Hsu, Danley C.; Ford, Eric B.; Terrien, Ryan C.

doi:10.1093/mnras/staa2391

Cited by 80 publications

(72 citation statements)

References 54 publications

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“…In the sample of mostly mid-and early-M dwarfs observed by Kepler on the other hand, Dressing & Charbonneau (2015) found 0.29 planets with radii 2−4 R ⊕ and periods 0.9 < P < 18.3 d, and 0.57 with radii 1−2 R ⊕ (these are not upper limits, but averages). The other studies collated by Mulders (2018) show similar results; see e.g Youdin ( 2011), Howard et al (2012), Dong & Zhu (2013), Petigura et al (2013), Morton & Swift (2014), Mulders et al (2015b), Silburt et al Gaidos et al (2016), and also Hsu et al (2019Hsu et al ( , 2020.…”

Section: Discussionmentioning

confidence: 54%

“…Remarkably, in a review of these results, Mulders (2018) highlights the fact that occurrence rates of sub-Neptunes (R < 4 R ⊕ ) rise with decreasing stellar mass -by a factor of three from the FGK stars to the M dwarfs. This trend has been explored down into the early and mid-M dwarfs, by for example Berta et al (2013), Dressing & Charbonneau (2015), Mulders et al (2015a), Muirhead et al (2015), Hardegree-Ullman et al (2019), and Hsu et al (2020). Ultracool dwarfs, at the lower-mass limit of the Planet eq.…”

Section: Introductionmentioning

confidence: 99%

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Occurrence rate of exoplanets orbiting ultracool dwarfs as probed by K2

Sestovic

Demory

2020

A&A

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Context. With the discovery of a planetary system around the ultracool dwarf TRAPPIST-1, there has been a surge of interest in such stars as potential planet hosts. Planetary systems around ultracool dwarfs represent our best chance of characterising temperate rocky-planet atmospheres with the James Webb Space Telescope. However, TRAPPIST-1 remains the only known system of its kind and the occurrence rate of planets around ultracool dwarfs is still poorly constrained. Aims. We seek to perform a complete transit search on the ultracool dwarfs observed by NASA’s K2 mission, and use the results to constrain the occurrence rate of planets around these stars. Methods. We filter and characterise the sample of ultracool dwarfs observed by K2 by fitting their spectral energy distributions and using parallaxes from Gaia. We build an automatic pipeline to perform photometry, detrend the light curves, and search for transit signals. Using extensive injection-recovery tests of our pipeline, we compute the detection sensitivity of our search, and thus the completeness of our sample. We infer the planetary occurrence rates within a hierarchical Bayesian model (HBM) to treat uncertain planetary parameters. With the occurrence rate parametrised by a step-wise function, we present a convenient way to directly marginalise over the second level of our HBM (the planetary parameters). Our method is applicable generally and can greatly speed up inference with larger catalogues of detected planets. Results. We detect one planet in our sample of 702 ultracool dwarfs: a previously validated mini-Neptune. We thus infer a mini-Neptune (2−4 R⊕) occurrence rate of η = 0.20−0.11+0.16 within orbital periods of 1−20 days. For super-Earths (1−2 R⊕) and ice or gas giants (4−6 R⊕) within 1−20 days, we place 95% credible intervals of η < 1.14 and η < 0.29, respectively. If TRAPPIST-1-like systems were ubiquitous, we would have a ~96% chance of finding at least one.

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Section: Discussionmentioning

confidence: 54%

Section: Introductionmentioning

confidence: 99%

Occurrence rate of exoplanets orbiting ultracool dwarfs as probed by K2

Sestovic

Demory

2020

A&A

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“…Figure 1 shows the orbital distribution of 273 terrestrial planets or sub-Neptune with masses smaller than 17 M⊕ around M dwarfs or stars with masses between 0.075 and 0.6 M⊙ (Mann et al 2015). The provided census further suggests that nearly 89% of planets locate at 0.01 to 0.3 AU away from their host stars, which is more likely to be detected combined with high occurrence rate of terrestrial planets around M dwarfs (Fressin et al 2013;Silburt et al 2015;Mulders et al 2015; ⋆ † E-mail: wangsu@pmo.ac.cn, jijh@pmo.ac.cn Hsu et al 2020). Therefore, the habitability, occurrence, formation and evolution of terrestrial planets around M dwarfs are of particular interests to the community.…”

Section: Introductionmentioning

confidence: 98%

The Terrestrial Planet Formation around M Dwarfs: In-situ, Inward Migration or Reversed Migration

Pan,

Wang,

2021

Preprint

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Terrestrial planets are commonly observed to orbit M dwarfs with close-in trajectories. In this work, we extensively perform N-body simulations of planetesimal accretion with three models of in-situ, inward migration and reversed migration to explore terrestrial formation in tightly compact systems of M dwarfs. In the simulations, the solid disks are assumed to be 0.01% of the masses of host stars and spread from 0.01 to 0.5 AU with the surface density profile scaling with r −k according to the observations. Our results show that in-situ scenario may produce 7.77 +3.23 −3.77 terrestrial planets with an average mass of 1.23 +4.01 −0.93 M ⊕ around M dwarfs. The number of planets tends to increase as the disk slope is steeper or with a larger stellar mass. Moreover, we show that 2.55 +1.45 −1.55 planets with mass of 3.76 +8.77 −3.46 M ⊕ are formed in the systems via inward migration, while 2.85 +1.15 −0.85 planets with 3.01 +13.77 −2.71 M ⊕ are yielded under reversed migration. Migration scenarios can also deliver plentiful water from the exterior of ice line to the interior due to more efficient accretion. The simulation outcomes of reversed migration model produce the best matching with observations, being suggestive of a likely mechanism for planetary formation around M dwarfs.

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“…The notion that AU Mic could be a host for several planets is not a surprising one. Indeed, the occurrence rate of planets with a radius between 0.5 R ⊕ and 4.0 R ⊕ and a period between 0.5 and 256 d is estimated as 8.4 +1.2 −1.1 planets per M dwarf (Hsu et al 2020), although the occurrence rate of more massive planets in M dwarfs decreases significantly with mass (e.g., Bonfils et al 2013). Moreover, provided the fact that AU Mic has an edgeon debris disk and that AU Mic b is a transiting planet with an aligned orbit, the chances that other planets also reside in coplanar orbits increase and, therefore, possible close-in additional planets are also likely to transit the star.…”

Section: Introductionmentioning

confidence: 99%

New constraints on the planetary system around the young active star AU Mic

Martioli

Hébrard

Correia

et al. 2021

A&A

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AU Microscopii (AU Mic) is a young, active star whose transiting planet was recently detected. Here, we report our analysis of its TESS light curve, where we modeled the BY Draconis type quasi-periodic rotational modulation by starspots simultaneously to the flaring activity and planetary transits. We measured a flare occurrence rate in AU Mic of 6.35 flares per day for flares with amplitudes in the range of 0.06% < fmax < 1.5% of the star flux. We employed a Bayesian Markov chain Monte Carlo analysis to model the five transits of AU Mic b observed by TESS, improving the constraints on the planetary parameters. The measured planet-to-star effective radius ratio of Rp∕R⋆ = 0.0496 ± 0.0007 implies a physical radius of 4.07 ± 0.17 R⊕ and a planet density of 1.4 ± 0.4 g cm−3, confirming that AU Mic b is a Neptune-size moderately inflated planet. While a single feature possibly due to a second planet was previously reported in the former TESS data, we report the detection of two additional transit-like events in the new TESS observations of July 2020. This represents substantial evidence for a second planet (AU Mic c) in the system. We analyzed its three available transits and obtained an orbital period of 18.859019 ± 0.000016 d and a planetary radius of 3.24 ± 0.16 R⊕, which defines AU Mic c as a warm Neptune-size planet with an expected mass in the range of 2.2 M⊕ < Mc < 25.0 M⊕, estimated from the population of exoplanets of similar sizes. The two planets in the AU Mic system are in near 9:4 mean-motion resonance. We show that this configuration is dynamically stable and should produce transit-timing variations (TTV). Our non-detection of significant TTV in AU Mic b suggests an upper limit for the mass of AU Mic c of <7 M⊕, indicating that this planet is also likely to be inflated. As a young multi-planet system with at least two transiting planets, AU Mic becomes a key system for the study of atmospheres of infant planets and of planet-planet and planet-disk dynamics at the early stages of planetary evolution.

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Occurrence rates of planets orbiting M Stars: applying ABC to Kepler DR25, Gaia DR2, and 2MASS data

Cited by 80 publications

References 54 publications

Occurrence rate of exoplanets orbiting ultracool dwarfs as probed by K2

Occurrence rate of exoplanets orbiting ultracool dwarfs as probed by K2

The Terrestrial Planet Formation around M Dwarfs: In-situ, Inward Migration or Reversed Migration

New constraints on the planetary system around the young active star AU Mic

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