Occurrence Rates from Direct Imaging Surveys

Bowler, Brendan P.; Nielsen, Eric L.

doi:10.1007/978-3-319-30648-3_155-1

Cited by 9 publications

(11 citation statements)

References 99 publications

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“…Radial velocity surveys indicate that giant planets inside 7 au only occur around 10% of FGK stars and they predominantly orbit their host stars at intermediate distances (3 − 5 au); their occurrence rate declines at both smaller and larger orbital distances (Cumming et al 2008;Howard et al 2012;Wittenmyer et al 2016;Fernandes et al 2019;Fulton et al 2019;Wittenmyer et al 2020; complemented by direct imaging surveys, e.g. Bowler & Nielsen 2018; Baron et al 2019). It is unclear why giant planets preferably occur at intermediate distances.…”

Section: Introductionmentioning

confidence: 99%

Radial Gradients in Dust-to-gas Ratio Lead to Preferred Region for Giant Planet Formation

Chachan

Lee

Knutson

2021

ApJ

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The Rosseland mean opacity of dust in protoplanetary disks is often calculated assuming the interstellar medium (ISM) size distribution and a constant dust-to-gas ratio. However, the dust size distribution and the dust-to-gas ratio in protoplanetary disks are distinct from those of the ISM. Here, we use simple dust evolution models that incorporate grain growth and transport to calculate the time evolution of mean opacity of dust grains as a function of distance from the star. Dust dynamics and size distribution are sensitive to the assumed value of the turbulence strength α t and the velocity at which grains fragment v frag . For moderate-to-low turbulence strengths of α t 10 −3 and substantial differences in v frag for icy and ice-free grains, we find a spatially nonuniform dust-to-gas ratio and grain size distribution that deviate significantly from the ISM values, in agreement with previous studies. The effect of non-uniform dust-to-gas ratio on the Rosseland mean opacity dominates over that of the size distribution. Spatially varying-that is non-monotonic-dust opacity creates a region in the protoplanetary disk that is optimal for producing hydrogen-rich planets, potentially explaining the apparent peak in gas giant planet occurrence rate at intermediate distances. Enhanced opacities within the ice line also suppress gas accretion rates onto sub-Neptune cores, thus stifling their tendency to undergo runaway gas accretion within disk lifetimes. Finally, our work corroborates the idea that low mass cores with large primordial gaseous envelopes ('super-puffs') originate beyond the ice line.

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Section: Introductionmentioning

confidence: 99%

Radial Gradients in Dust-to-gas Ratio Lead to Preferred Region for Giant Planet Formation

Chachan

Lee

Knutson

2021

ApJ

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“…With its first direct detections already some ten to fifteen years ago (Chauvin et al 2004;Marois et al 2008), the technique of direct imaging has started to reveal a scarce but interesting population of planets or very-low-mass substellar objects at large separations from their host stars (Bowler 2016;Bowler & Nielsen 2018;Wagner et al 2019). The formation mechanism of individual detections is often not obvious but gravitational instability as well as core accretion (with the inclusion of N-body interactions during the formation phase and in the first few million years afterwards) are likely candidates to explain the origin of at least some of these systems (e.g., Marleau et al 2019).…”

Section: Introductionmentioning

confidence: 99%

The Planetary Accretion Shock. II. Grid of Postshock Entropies and Radiative Shock Efficiencies for Nonequilibrium Radiation Transport

Marleau

Mordasini

Kuiper

2019

ApJ

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In the core-accretion formation scenario of gas giants, most of the gas accreting onto a planet is processed through an accretion shock. In this series of papers we study this shock since it is key in setting the forming planet's structure and thus its post-formation luminosity, with dramatic observational consequences. We perform one-dimensional grey radiation-hydrodynamical simulations with non-equilibrium (two-temperature) radiation transport and up-to-date opacities. We survey the parameter space of accretion rate, planet mass, and planet radius and obtain post-shock temperatures, pressures, and entropies, as well as global radiation efficiencies. We find that usually, the shock temperature T shock is given by the "free-streaming" limit. At low temperatures the dust opacity can make the shock hotter but not significantly. We corroborate this with an original semi-analytical derivation of T shock . We also estimate the change in luminosity between the shock and the nebula. Neither T shock nor the luminosity profile depend directly on the optical depth between the shock and the nebula. Rather, T shock depends on the immediate pre-shock opacity, and the luminosity change on the equation of state (EOS). We find quite high immediate post-shock entropies (S ≈ 13-20 k B m H −1 ), which makes it seem unlikely that the shock can cool the planet. The global radiation efficiencies are high (η phys 97 %) but the remainder of the total incoming energy, which is brought into the planet, exceeds the internal luminosity of classical cold starts by orders of magnitude. Overall, these findings suggest that warm or hot starts are more plausible.

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“…These high-viscosity models introduce some challenges in the modeling of the observed mass function of exoplanets especially around stars with multiple gas giant if these planets are formed over a range of time prior to or during disk clearing stage (see discussions in §2). They are also difficult to reconcile with the simulations (Zhang et al 2018;Lodato et al 2019) of the ALMA maps of PSDs with gaps (Andrews et al 2018;Long et al 2018) and the sparsity of massive gas giants with wide orbits (Meshkat et al 2017;Vigan et al 2017;Bowler & Nielsen 2018). Based on these considerations, we suggest typical Jupiter mass giants were born in disks with relatively low viscosity.…”

Section: Tidal Barrier For Jupiter-size Giants: Accretion Rates and F...mentioning

confidence: 58%

Accretion of Gas Giants Constrained by the Tidal Barrier

Chen

Lin

et al. 2020

Preprint

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After protoplanets have acquired sufficient mass to open partial gaps in their natal protostellar disks, residual gas continues to diffuse onto horseshoe streamlines under effect of viscous dissipation, and meander in and out of the planets' Hill sphere. Within the Hill sphere, the horseshoe streamlines intercept gas flow in circumplanetary disks. The host stars' tidal perturbation induces a barrier across the converging streamlines' interface. Viscous transfer of angular momentum across this tidal barrier determines the rate of mass diffusion from the horseshoe streamlines onto the circumplanetary disks, and eventually the accretion rate onto the protoplanets. We carry out a series of numerical simulations to test the influence of this tidal barrier on super-thermal planets. In weakly viscous disks, protoplanets' accretion rate steeply decreases with their masses above the thermal limit. As their growth timescale exceeds the gas depletion time scale, their masses reach asymptotic values comparable to that of Jupiter. In relatively thick and strongly viscous disks, protoplanets' asymptotic masses exceed several times that of Jupiter. Two dimensional numerical simulations show that such massive protoplanets strongly excite the eccentricity of nearby horseshoe streamlines, destabilize orderly flow, substantially enhance the diffusion rate across the tidal barrier, and elevate their growth rate until their natal disk is severely depleted. In contrast, eccentric streamlines remain stable in three dimensional simulations. Based on the upper fall-off in the observe mass distribution of known exoplanets, we suggest their natal disks had relatively low viscosity (α ∼ 10 −3), modest thickness (H/R ∼ 0.03 − 0.05), and limited masses (comparable to that of minimum mass solar nebula model).

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Occurrence Rates from Direct Imaging Surveys

Cited by 9 publications

References 99 publications

Radial Gradients in Dust-to-gas Ratio Lead to Preferred Region for Giant Planet Formation

Radial Gradients in Dust-to-gas Ratio Lead to Preferred Region for Giant Planet Formation

The Planetary Accretion Shock. II. Grid of Postshock Entropies and Radiative Shock Efficiencies for Nonequilibrium Radiation Transport

Accretion of Gas Giants Constrained by the Tidal Barrier

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