Threshold Radii of Volatile-rich Planets Lozovsky, M.; Helled, R.; Dorn, C. ...
Astrophysical journal/The Astrophysical journal,
10/2018, Letnik:
866, Številka:
1
Journal Article
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Constraining the planetary composition is essential for exoplanetary characterization. In this paper, we use a statistical analysis to determine the characteristic maximum (threshold) radii for ...various compositions for exoplanets with masses up to 25 Earth masses (M⊕). We confirm that most planets with radii larger than 1.6 Earth radii (R⊕) are not rocky, and must consist of lighter elements, as found by previous studies. We find that planets with radii above 2.6 R⊕ cannot be pure-water worlds, and must contain significant amounts of hydrogen and helium (H-He). We find that planets with radii larger than about 3 R⊕, 3.6 R⊕, and 4.3 R⊕ are expected to consist of 2%, 5%, and 10% of H-He, respectively. We investigate the sensitivity of the results to the assumed internal structure, the planetary temperature and albedo, and the accuracy of the determination of mass and radius. We show that the envelope's metallicity, the percentage of H-He, and the distribution of the elements play a significant role in the determination of the threshold radius. Finally, we conclude that, despite the degenerate nature of the problem, it is possible to put limits on the possible range of compositions for planets with well-measured mass and radius.
This paper deals with the thermodynamic analysis, of both the first and second law of thermodynamic of two different technologies, (ORC and Kalina cycle) for power production through an enhanced ...geothermal system (EGS). In order to find a better performance of both thermal cycles it were evaluated 15 different working fluids for ORC and three different composition of the ammonia–water mixture for the Kalina cycle. In this work, the Aspen-HYSYS software was used to simulate both thermal cycles and to calculate the thermodynamic properties based on Peng–Robinson Stryjek–Vera (PRSV) Equation of State (EoS). At the end the two cycles was compared using an economic analysis with the fluid that offers the best performance for each thermal cycle which are R-290 for ORC and for Kalina cycle a composition of the mixture of 84% of ammonia mass fraction and 16% of water mass fraction. For this conditions the Kalina cycle produce 18% more net power than the ORC. A levelized electricity costs of 0.22 €/kW h was reached for ORC and 0.18 €/kW h for Kalina cycle. Finally a sensitivity analysis of the EGS LCOE was carried out for a few economic parameters to determinate how is the variation of LCOE for a % change from the base case.
► The aim of this paper is to compare both cycles (ORC and Kalina). ► Kalina cycle offer 18% more net power than ORC and require 37% less mass flow rate. ► It was obtained 17.8% lower levelized electricity costs for Kalina cycle over the ORC.
Context. Within the core accretion scenario of planetary formation, most simulations performed so far always assume the accreting envelope to have a solar composition. From the study of meteorite ...showers on Earth and numerical simulations, we know that planetesimals must undergo thermal ablation and disruption when crossing a protoplanetary envelope. Thus, once the protoplanet has acquired an atmosphere, not all planetesimals reach the core intact, i.e. the primordial envelope (mainly H and He) gets enriched in volatiles and silicates from the planetesimals. This change of envelope composition during the formation can have a significant effect on the final atmospheric composition and on the formation timescale of giant planets. Aims. We investigate the physical implications of considering the envelope enrichment of protoplanets due to the disruption of icy planetesimals during their way to the core. Particular focus is placed on the effect on the critical core mass for envelopes where condensation of water can occur. Methods. Internal structure models are numerically solved with the implementation of updated opacities for all ranges of metallicities and the software Chemical Equilibrium with Applications to compute the equation of state. This package computes the chemical equilibrium for an arbitrary mixture of gases and allows the condensation of some species, including water. This means that the latent heat of phase transitions is consistently incorporated in the total energy budget. Results. The critical core mass is found to decrease significantly when an enriched envelope composition is considered in the internal structure equations. A particularly strong reduction of the critical core mass is obtained for planets whose envelope metallicity is larger than Z ≈ 0.45 when the outer boundary conditions are suitable for condensation of water to occur in the top layers of the atmosphere. We show that this effect is qualitatively preserved even when the atmosphere is out of chemical equilibrium. Conclusions. Our results indicate that the effect of water condensation in the envelope of protoplanets can severely affect the critical core mass, and should be considered in future studies.
Aims.
It has been suggested that planetary radii increase with stellar mass for planet sizes smaller than 6
R
⊕
and host masses lower than 1
M
⊙
. In this study, we explore whether this inferred ...relation of planetary size and host star mass can be explained by a higher planetary mass of planets orbiting higher-mass stars, inflation of the planetary radius due to the difference in stellar irradiation, or different planetary compositions and structures.
Methods.
Using exoplanetary data of planets with measured masses and radii, we investigated the relations between stellar mass and various planetary properties for G and K stars. We confirm that more massive stars host larger and more massive planets.
Results.
We find that the differences in the planetary masses and temperatures are insufficient to explain the measured differences in radii for planets surrounding different stellar types. We show that the larger planetary radii can be explained by a larger fraction of volatile material (H-He atmospheres) in planets surrounding more massive stars.
Conclusions.
We conclude that planets around more massive stars are most probably larger as a result of larger H-He atmospheres. Our findings imply that planets forming around more massive stars tend to accrete H-He atmospheres more efficiently.
The radius valley separating super-Earths from mini-Neptunes is a fundamental benchmark for theories of planet formation and evolution. Observations show that the location of the radius valley ...decreases with decreasing stellar mass and with increasing orbital period. Here, we build on our previous pebble-based formation model. Combined with photoevaporation after disc dispersal, it has allowed us to unveil the radius valley as a separator between rocky and water-worlds. In this study, we expand our model for a range of stellar masses spanning from 0.1 to 1.5 M ⊙ . We find that the location of the radius valley is well described by a power-law in stellar mass as R valley = 1.8197 M ⋆ 0.14(+0.02/−0.01) , which is in excellent agreement with observations. We also find very good agreement with the dependence of the radius valley on orbital period, both for FGK and M dwarfs. Additionally, we note that the radius valley gets filled towards low stellar masses, particularly at 0.1–0.4 M ⊙ , yielding a rather flat slope in R valley − P orb . This is the result of orbital migration occurring at lower planet mass for less massive stars, which allows for low-mass water-worlds to reach the inner regions of the system, blurring the separation in mass (and size) between rocky and water worlds. Furthermore, we find that for planetary equilibrium temperatures above 400 K, the water in the volatile layer exists fully in the form of steam, puffing the planet radius up (as compared to the radii of condensed-water worlds). This produces an increase in planet radii of ∼30% at 1 M ⊕ and of ∼15% at 5 M ⊕ compared to condensed-water worlds. As with Sun-like stars, we find that pebble accretion leaves its imprint on the overall exoplanet population as a depletion of planets with intermediate compositions (i.e. water mass fractions of ∼0 − 20%), carving an planet-depleted diagonal band in the mass-radius (MR) diagrams. This band is better visualised when plotting the planet’s mean density in terms of an Earth-like composition. This change in coordinates causes the valley to emerge for all the stellar mass cases.
DNMT3A encodes an enzyme that carries out de novo DNA methylation, which is essential for the acquisition of cellular identity and specialized functions during cellular differentiation. DNMT3A is the ...most frequently mutated gene in age-related clonal hematopoiesis. As such, mature immune cells harboring DNMT3A mutations can be readily detected in elderly persons. Most DNMT3A mutations associated with clonal hematopoiesis are heterozygous and predicted to cause loss of function, indicating that haploinsufficiency is the predominant pathogenic mechanism. Yet, the impact of DNMT3A haploinsufficiency on the function of mature immune cells is poorly understood. Here, we demonstrate that DNMT3A haploinsufficiency impairs the gain of DNA methylation at decommissioned enhancers, while simultaneously and unexpectedly impairing DNA demethylation of newly activated enhancers in mature human myeloid cells. The DNA methylation defects alter the activity of affected enhancers, leading to abnormal gene expression and impaired immune response. These findings provide insights into the mechanism of immune dysfunction associated with clonal hematopoiesis and acquired DNMT3A mutations.
We report the discovery of a hot Jupiter on a 3.28-day orbit around a 1.08
M
⊙
G0 star that is the secondary component in a loose binary system. Based on follow-up radial velocity observations of ...TOI-858 B with CORALIE on the Swiss 1.2 m telescope and CHIRON on the 1.5 m telescope at the Cerro Tololo Inter-American Observatory (CTIO), we measured the planet mass to be 1.10
−0.07
+0.08
M
J
. Two transits were further observed with CORALIE to determine the alignment of TOI-858 B b with respect to its host star. Analysis of the Rossiter-McLaughlin signal from the planet shows that the sky-projected obliquity is
λ
= 99.3
−3.7
+3.8°
. Numerical simulations show that the neighbour star TOI-858 A is too distant to have trapped the planet in a Kozai–Lidov resonance, suggesting a different dynamical evolution or a primordial origin to explain this misalignment. The 1.15
M
⊙
primary F9 star of the system (TYC 8501-01597-1, at
ρ
~11″) was also observed with CORALIE in order to provide upper limits for the presence of aplanetary companion orbiting that star.
Context. Computing the mass of planetary envelopes and the critical mass beyond which planets accrete gas in a runaway fashion is important for studying planet formation, in particular, for planets ...up to the Neptune-mass range. This computation in principle requires solving a set of differential equations, the internal structure equations, for some boundary conditions (pressure, temperature in the protoplanetary disc where a planet forms, core mass, and the rate of accretion of solids by the planet). Solving these equations in turn proves to be time-consuming and sometimes numerically unstable. Aims. The aim is to provide a way to approximate the result of integrating the internal structure equations for a variety of boundary conditions. Methods. We computed a set of internal planetary structures for a very large number (millions) of boundary conditions, considering two opacities: that of the interstellar medium, and a reduced opacity. This database was then used to train deep neural networks (DNN) in order to predict the critical core mass and the mass of planetary envelopes as a function of the boundary conditions. Results. We show that our neural networks provide a very good approximation (at the percent level) of the result obtained by solving interior structure equations, but the required computer time is much shorter. The difference with the real solution is much smaller than the difference that is obtained with some analytical formulas that are available in the literature, which only provide the correct order of magnitude at best. We compare the results of the DNN with other popular machine-learning methods (random forest, gradient boost, support vector regression) and show that the DNN outperforms these methods by a factor of at least two. Conclusions. We show that some analytical formulas that can be found in various papers can severely overestimate the mass of planets and therefore predict the formation of planets in the Jupiter-mass regime instead of the Neptune-mass regime. The python tools that we provide allow computing the critical mass and the mass of planetary envelopes in a variety of cases, without the requirement of solving the internal structure equations. These tools can easily replace previous analytical formulas and provide far more accurate results.
•FRGO-PN nanocomposites were prepared via a simple chemical method.•Interaction at the interface and structural changes were investigated using TEM, Raman and infrared spectroscopy.•Optical ...absorption, steady state and time resolved photoluminescence elucidated the interaction between both components.•FRGO had like effect a PL quenching and an increase of the exciton lifetime in porphyrin nanorods.•Our results show an important charge transfer between FRGO and PN.
Few layers of reduced graphene oxide (FRGO) were functionalized with porphyrins self assembled nanostructure. These new hybrid nanocomposites were investigated using Transmission Electron Microscopy (TEM), UV–visible, Raman scattering, Fourier transform infrared (FT-IR) and photoluminescence. The structural and morphological results show strong interactions between these hybrids components. Moreover, steady state photoluminescence (PL) of both porphyrin nanorods (PN) and (PN)/FRGO composite show clearly the PL quenching confirming a charge transfer from porphyrin molecules to graphene sheets. In addition, the relaxation kinetics of the PN and (PN)/FRGO were studied by means of time resolved photoluminescence (TR-PL) and the excitation density in the sample was of 1017cm3/pulse. The major change of the carrier dynamics in porphyrin nanorods after their interaction with FRGO was in the increase in the fast time constants, which found to be slower at 650nm, τ1=196ps and τ2=1171ps. This has been explained by the change in their energy band gap due to the role of FRGO as doping related to the size of the nanometer-scale sp2 clusters, which leads to a slower interband carrier recombination.
In general, the presence of Fe2O3 is claimed to reduce the insulating behavior of electrical porcelains, even if a rigorous proof has not yet been reported. The purpose of this study was to evaluate ...the real influence of Fe2O3 content on the electrical resistivity of a standard aluminous porcelain widely used in insulators. The electrical resistivity for the composition with 3wt% Fe2O3 was higher than those found for standard aluminous porcelain, which was discussed in terms of the concentration of glassy and mullite phases. A reduction in the electrical resistivity was only observed in porcelain samples containing over 3wt% Fe2O3. The presence of hematite phase was considered responsible for this reduction. These results suggest that low-cost raw materials with greater Fe2O3 content should not extensively affect the insulating properties and could therefore be used in manufacturing aluminous electrical porcelain.
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