Showing papers on "Radiative transfer published in 2019"

Radiative sky cooling: Fundamental principles, materials, and applications

Abstract: Radiative sky cooling cools an object on the earth by emitting thermal infrared radiation to the cold universe through the atmospheric window (8–13 μm). It consumes no electricity and has great potential to be explored for cooling of buildings, vehicles, solar cells, and even thermal power plants. Radiative sky cooling has been explored in the past few decades but limited to nighttime use only. Very recently, owing to the progress in nanophotonics and metamaterials, daytime radiative sky cooling to achieve subambient temperatures under direct sunlight has been experimentally demonstrated. More excitingly, the manufacturing of the daytime radiative sky cooling material by the roll-to-roll process makes large-scale deployment of the technology possible. This work reviews the fundamental principles of radiative sky cooling as well as the recent advances, from both materials and systems point of view. Potential applications in different scenarios are reviewed with special attention to technology viability and benefits. As the energy situation and environmental issues become more and more severe in the 21st century, radiative sky cooling can be explored for energy saving in buildings and vehicles, mitigating the urban heat island effect, resolving water and environmental issues, achieving more efficient power generation, and even fighting against the global warming problem.

petitRADTRANS. A Python radiative transfer package for exoplanet characterization and retrieval

Abstract: We present the easy-to-use, publicly available, Python package petitRADTRANS, built for the spectral characterization of exoplanet atmospheres. The code is fast, accurate, and versatile; it can calculate both transmission and emission spectra within a few seconds at low resolution (λ /Δλ = 1000; correlated-k method) and high resolution (λ /Δλ = 106 ; line-by-line method), using only a few lines of input instruction. The somewhat slower, correlated-k method is used at low resolution because it is more accurate than methods such as opacity sampling. Clouds can be included and treated using wavelength-dependent power law opacities, or by using optical constants of real condensates, specifying either the cloud particle size, or the atmospheric mixing and particle settling strength. Opacities of amorphous or crystalline, spherical or irregularly-shaped cloud particles are available. The line opacity database spans temperatures between 80 and 3000 K, allowing to model fluxes of objects such as terrestrial planets, super-Earths, Neptunes, or hot Jupiters, if their atmospheres are hydrogen-dominated. Higher temperature points and species will be added in the future, allowing to also model the class of ultra hot-Jupiters, with equilibrium temperatures T eq ≳ 2000 K. Radiative transfer results were tested by cross-verifying the low- and high-resolution implementation of petitRADTRANS, and benchmarked with the petitCODE, which itself is also benchmarked to the ATMO and Exo-REM codes. We successfully carried out test retrievals of synthetic JWST emission and transmission spectra (for the hot Jupiter TrES-4b, which has a T eq of ∼1800 K).

Super-Eddington Accretion Disks around Supermassive Black Holes

Abstract: We use global three dimensional radiation magneto-hydrodynamical simulations to study accretion disks onto a $5\times 10^8M_{\odot}$ black hole with accretion rates varying from $\sim 250L_{Edd}/c^2$ to $1500 L_{Edd}/c^2$. We form the disks with torus centered at $50-80$ gravitational radii with self-consistent turbulence initially generated by the magneto-rotational instability. We study cases with and without net vertical magnetic flux. The inner regions of all disks have radiation pressure $\sim 10^4-10^6$ times the gas pressure. Non-axisymmetric density waves that steepen into spiral shocks form as gas flows towards the black hole. In simulations without net vertical magnetic flux, Reynolds stress generated by the spiral shocks are the dominant mechanism to transfer angular momentum. Maxwell stress from MRI turbulence can be larger than the Reynolds stress only when net vertical magnetic flux is sufficiently large. Outflows are formed with speed $\sim 0.1-0.4c$. When the accretion rate is smaller than $\sim 500 L_{Edd}/c^2$, outflows start around $10$ gravitational radii and the radiative efficiency is $\sim 5\%-7\%$ with both magnetic field configurations. With accretion rate reaching $1500 L_{Edd}/c^2$, most of the funnel region close to the rotation axis becomes optically thick and the outflow only develops beyond $50$ gravitational radii. The radiative efficiency is reduced to $1\%$. We always find the kinetic energy luminosity associated with the outflow is only $\sim 15\%-30\%$ of the radiative luminosity. The mass flux lost in the outflow is $\sim 15\%-50\%$ of the net mass accretion rates. We discuss implications of our simulation results on the observational properties of these disks.

Modern stellar spectroscopy caveats

Abstract: Multiple codes are available to derive atmospheric parameters and individual chemical abundances from high-resolution spectra of AFGKM stars. Almost all spectroscopists have their own preferences regarding which code and method to use. But the intrinsic differences between codes and methods lead to complex systematics that depend on multiple variables such as the selected spectral regions and the radiative transfer code used. I expand iSpec, a popular open-source spectroscopic tool, to support the most well-known radiative transfer codes and assess their similarities and biases when using multiple set-ups based on the equivalent-width method and the synthetic spectral-fitting technique (interpolating from a pre-computed grid of spectra or synthesizing with interpolated model atmospheres). This work shows that systematic differences on atmospheric parameters and abundances between most of the codes can be reduced when using the same method and executing a careful spectral feature selection. However, it may not be possible to ignore the remaining differences, depending on the particular case and the required precision. Regarding methods, equivalent-width-based and spectrum-fitting analyses exhibit large differences that are caused by their intrinsic differences, which is significant given the popularity of these two methods. The results help to identify the key caveats of modern spectroscopy that all scientists should be aware of before trusting their own results or being tempted to combine atmospheric parameters and abundances from the literature.

MeV-scale reheating temperature and thermalization of oscillating neutrinos by radiative and hadronic decays of massive particles

Abstract: From a theoretical point of view, there is a strong motivation to consider an MeV-scale reheating temperature induced by long-lived massive particles with masses around the weak scale, decaying only through gravitational interaction. In this study, we investigate lower limits on the reheating temperature imposed by big-bang nucleosynthesis assuming both radiative and hadronic decays of such massive particles. For the first time, effects of neutrino self-interactions and oscillations are taken into account in the neutrino thermalization calculations. By requiring consistency between theoretical and observational values of light element abundances, we find that the reheating temperature should conservatively be $T_{\rm RH} \gtrsim 1.8$ MeV in the case of the 100% radiative decay, and $T_{\rm RH} \gtrsim$ 4-5 MeV in the case of the 100% hadronic decays for particle masses in the range of 10 GeV to 100 TeV.

MeV-scale reheating temperature and thermalization of oscillating neutrinos by radiative and hadronic decays of massive particles

Abstract: From a theoretical point of view, there is a strong motivation to consider an MeV-scale reheating temperature induced by long-lived massive particles with masses around the weak scale, decaying only through gravitational interaction. In this study, we investigate lower limits on the reheating temperature imposed by big-bang nucleosynthesis assuming both radiative and hadronic decays of such massive particles. For the first time, effects of neutrino self-interactions and oscillations are taken into account in the neutrino thermalization calculations. By requiring consistency between theoretical and observational values of light element abundances, we find that the reheating temperature should conservatively be $T_{\rm RH} \gtrsim 1.8$ MeV in the case of the 100% radiative decay, and $T_{\rm RH} \gtrsim$ 4-5 MeV in the case of the 100% hadronic decays for particle masses in the range of 10 GeV to 100 TeV.

Full transport model of GW170817-like disk produces a blue kilonova

Abstract: The 2017 detection of the inspiral and merger of two neutron stars in gravitational waves and gamma rays was accompanied by a quickly-reddening transient. Such a transient was predicted to occur following a rapid neutron capture (r-process) nucleosynthesis event, which synthesizes neutron-rich, radioactive nuclei and can take place in both dynamical ejecta and in the wind driven off the accretion torus formed after a neutron star merger. We present the first three-dimensional general relativistic, full transport neutrino radiation magnetohydrodynamics (GRRMHD) simulations of the black hole-accretion disk-wind system produced by the GW170817 merger. We show that the small but non-negligible optical depths lead to neutrino transport globally coupling the disk electron fraction, which we capture by solving the transport equation with a Monte Carlo method. The resulting absorption drives up the electron fraction in a structured, continuous outflow, with electron fraction as high as $Y_e\sim 0.4$ in the extreme polar region. We show via nuclear reaction network and radiative transfer calculations that nucleosynthesis in the disk wind will produce a blue kilonova.

petitRADTRANS: a Python radiative transfer package for exoplanet characterization and retrieval.

Abstract: We present the easy-to-use, publicly available, Python package petitRADTRANS, built for the spectral characterization of exoplanet atmospheres. The code is fast, accurate, and versatile; it can calculate both transmission and emission spectra within a few seconds at low resolution ($\lambda/\Delta\lambda$ = 1000; correlated-k method) and high resolution ($\lambda/\Delta\lambda = 10^6$; line-by-line method), using only a few lines of input instruction. The somewhat slower correlated-k method is used at low resolution because it is more accurate than methods such as opacity sampling. Clouds can be included and treated using wavelength-dependent power law opacities, or by using optical constants of real condensates, specifying either the cloud particle size, or the atmospheric mixing and particle settling strength. Opacities of amorphous or crystalline, spherical or irregularly-shaped cloud particles are available. The line opacity database spans temperatures between 80 and 3000 K, allowing to model fluxes of objects such as terrestrial planets, super-Earths, Neptunes, or hot Jupiters, if their atmospheres are hydrogen-dominated. Higher temperature points and species will be added in the future, allowing to also model the class of ultra hot-Jupiters, with equilibrium temperatures $T_{\rm eq} \gtrsim 2000$ K. Radiative transfer results were tested by cross-verifying the low- and high-resolution implementation of petitRADTRANS, and benchmarked with the petitCODE, which itself is also benchmarked to the ATMO and Exo-REM codes. We successfully carried out test retrievals of synthetic JWST emission and transmission spectra (for the hot Jupiter TrES-4b, which has a $T_{\rm eq}$ of $\sim$ 1800 K). The code is publicly available at this http URL, and its documentation can be found at this https URL.

A hybrid investigation on numerical and analytical solutions of electro-magnetohydrodynamics flow of nanofluid through porous media with entropy generation

Abstract: The purpose of this paper is to present the investigation of the pressure-driven flow of aluminum oxide-water based nanofluid with the combined effect of entropy generation and radiative electro-magnetohydrodynamics filled with porous media inside a symmetric wavy channel.,The non-linear coupled differential equations are first converted into a number of ordinary differential equations with appropriate transformations and then analytical solutions are obtained by homotopic approach. Numerical simulation has been designed by the most efficient approach known homotopic-based Mathematica package BVPh 2.0 technique. The long wavelength approximation over the channel walls is taken into account. The obtained analytical results have been validated through graphs to infer the role of most involved pertinent parameters, whereas the characteristics of heat transfer and shear stress phenomena are presented and examined numerically.,It is found that the velocity profile decreases near to the channel. This is in accordance with the physical expectation because resistive force acts opposite the direction of fluid motion, which causes a decrease in velocity. It is seen that when the electromagnetic parameter increases then the velocity close to the central walls decreases whereas quite an opposite behavior is noted near to the walls. This happens because of the combined influence of electro-magnetohydrodynamics. It is perceived that by increasing the magnetic field parameter, Darcy number, radiation parameter, electromagnetic parameter and the temperature profile increases, and this is because of thermal buoyancy effect. For radiation and electromagnetic parameters, energy loss at the lower wall has substantial impact compared to the upper wall. Residual error minimizes at 20th order iterations.,The proposed prospective model is designed to explore the simultaneous effects of aluminum oxide-water base nanofluid, electro-magnetohydrodynamics and entropy generation through porous media. To the best of author’s knowledge, this model is reported for the first time.

Effects of a fully 3D atmospheric structure on exoplanet transmission spectra: retrieval biases due to day–night temperature gradients

Abstract: Transmission spectroscopy provides us with information on the atmospheric properties at the limb, which is often intuitively assumed to be a narrow annulus around the planet. Consequently, studies have focused on the effect of atmospheric horizontal heterogeneities along the limb. Here we demonstrate that the region probed in transmission – the limb – actually extends significantly towards the day and night sides of the planet. We show that the strong day–night thermal and compositional gradients expected on synchronous exoplanets create sufficient heterogeneities across the limb that result in important systematic effects on the spectrum and bias its interpretation. To quantify these effects, we developed a 3D radiative-transfer model able to generate transmission spectra of atmospheres based on 3D atmospheric structures. We first apply this tool to a simulation of the atmosphere of GJ 1214 b to produce synthetic JWST observations and show that producing a spectrum using only atmospheric columns at the terminator results in errors greater than expected noise. This demonstrates the necessity for a real 3D approach to model data for such precise observatories. Secondly, we investigate how day–night temperature gradients cause a systematic bias in retrieval analysis performed with 1D forward models. For that purpose we synthesise a large set of forward spectra for prototypical HD 209458 b- and GJ 1214 b-type planets varying the temperatures of the day and night sides as well as the width of the transition region. We then perform typical retrieval analyses and compare the retrieved parameters to the ground truth of the input model. This study reveals systematic biases on the retrieved temperature (found to be higher than the terminator temperature) and abundances. This is due to the fact that the hotter dayside is more extended vertically and screens the nightside – a result of the non-linear properties of atmospheric transmission. These biases will be difficult to detect as the 1D profiles used in the retrieval procedure are found to provide an excellent match to the observed spectra based on standard fitting criteria. This must be kept in mind when interpreting current and future data.

STiC: A multiatom non-LTE PRD inversion code for full-Stokes solar observations

Abstract: The inference of the underlying state of the plasma in the solar chromosphere remains extremely challenging because of the nonlocal character of the observed radiation and plasma conditions in this layer. Inversion methods allow us to derive a model atmosphere that can reproduce the observed spectra by undertaking several physical assumptions. The most advanced approaches involve a depth-stratified model atmosphere described by temperature, line-of-sight velocity, turbulent velocity, the three components of the magntic field vector, and gas and electron pressure. The parameters of the radiative transfer equation are computed from a solid ground of physical principles. In order to apply these techniques to spectral lines that sample the chromosphere, nonlocal thermodynamical equilibrium effects must be included in the calculations. We developed a new inversion code STiC (STockholm inversion Code) to study spectral lines that sample the upper chromosphere. The code is based on the RH forward synthesis code, which we modified to make the inversions faster and more stable. For the first time, STiC facilitates the processing of lines from multiple atoms in non-LTE, also including partial redistribution effects (PRD) in angle and frequency of scattered photons. Furthermore, we include a regularization strategy that allows for model atmospheres with a complex depth stratification, without introducing artifacts in the reconstructed physical parameters, which are usually manifested in the form of oscillatory behavior. This approach takes steps toward a node-less inversion, in which the value of the physical parameters at each grid point can be considered a free parameter. In this paper we discuss the implementation of the aforementioned techniques, the description of the model atmosphere, and the optimizations that we applied to the code. We carry out some numerical experiments to show the performance of the code and the regularization techniques that we implemented. We made STiC publicly available to the community.

Optical properties of ice and snow.

Abstract: The interactions of electromagnetic radiation with ice, and with ice-containing media such as snow and clouds, are determined by the refractive index and absorption coefficient (the 'optical constants') of pure ice as functions of wavelength. Bulk reflectance, absorptance and transmittance are further influenced by grain size (for snow), bubbles (for glacier ice and lake ice) and brine inclusions (for sea ice). Radiative transfer models for clouds can also be applied to snow; the important differences in their radiative properties are that clouds are optically thinner and contain smaller ice crystals than snow. Absorption of visible and near-ultraviolet radiation by ice is so weak that absorption of sunlight at these wavelengths in natural snow is dominated by trace amounts of light-absorbing impurities such as dust and soot. In the thermal infrared, ice is moderately absorptive, so snow is nearly a blackbody, with emissivity 98-99%. The absorption spectrum of liquid water resembles that of ice from the ultraviolet to the mid-infrared. At longer wavelengths they diverge, so microwave emission can be used to detect snowmelt on ice sheets, and to discriminate between sea ice and open water, by remote sensing. Snow and ice are transparent to radio waves, so radar can be used to infer ice-sheet thickness. This article is part of the theme issue 'The physics and chemistry of ice: scaffolding across scales, from the viability of life to the formation of planets'.

Biophysical feedback of global forest fires on surface temperature.

Abstract: The biophysical feedbacks of forest fire on Earth’s surface radiative budget remain uncertain at the global scale. Using satellite observations, we show that fire-induced forest loss accounts for about 15% of global forest loss, mostly in northern high latitudes. Forest fire increases surface temperature by 0.15 K (0.12 to 0.19 K) one year following fire in burned area globally. In high-latitudes, the initial positive climate-fire feedback was mainly attributed to reduced evapotranspiration and sustained for approximately 5 years. Over longer-term (> 5 years), increases in albedo dominated the surface radiative budget resulting in a net cooling effect. In tropical regions, fire had a long-term weaker warming effect mainly due to reduced evaporative cooling. Globally, biophysical feedbacks of fire-induced surface warming one year after fire are equivalent to 62% of warming due to annual fire-related CO2 emissions. Our results suggest that changes in the severity and/or frequency of fire disturbance may have strong impacts on Earth’s surface radiative budget and climate, especially at high latitudes. Understanding the role of forest fires in Earth’s climate system is critical to predict future fire-climate interactions. Here the authors show that fire-induced forest loss accounts for ~15% of global forest loss and that its impact on surface temperature depends on evapotranspiration and albedo.

Rotational disruption of dust grains by radiative torques in strong radiation fields

Abstract: Massive stars, supernovae, and kilonovae are among the most luminous radiation sources in the Universe. Observations usually show near- to mid-infrared (NIR–MIR, λ ≈ 1–5 μm) emission excess from H ii regions around young massive star clusters. Early-phase observations in optical-to-NIR wavelengths of type Ia supernovae also reveal unusual properties of dust extinction and dust polarization. The most common explanation for such NIR−MIR excess and unusual dust properties is the predominance of small grains (size a ≲ 0.05 μm) relative to large grains (a ≳ 0.1 μm) in the local environment of these strong radiation sources. However, why small grains might be predominant in these environments is unclear. Here we report a mechanism of dust destruction based on centrifugal stress within extremely fast-rotating grains spun-up by radiative torques, which we term radiative torque disruption (RATD). We find that RATD can disrupt large grains located within a distance of about a parsec from a massive star of luminosity L ≈ 104L⊙, where L⊙ is the solar luminosity, or from a supernova. This disruption effect increases the abundance of small grains relative to large grains and successfully reproduces the observed NIR−MIR excess and anomalous dust extinction/polarization. We apply the RATD mechanism for kilonovae and find that dust within about 0.1 parsec would be dominated by small grains. Small grains produced by RATD can also explain the steep far-ultraviolet rise in extinction curves towards starburst and high-redshift galaxies, and the decrease of the escape fraction of Lyman α photons from H ii regions surrounding young massive star clusters. A predominance of small grains (tens of nanometres in size) over larger grains and the corresponding near- to mid-infrared excess radiation from H ii regions around massive stars and supernovae has been difficult to explain. Hoang et al. propose a radiative torque disruption method for large dust grains that fits with the observational constraints.

Impact of Clouds and Hazes on the Simulated JWST Transmission Spectra of Habitable Zone Planets in the TRAPPIST-1 System

Abstract: The TRAPPIST-1 system, consisting of an ultra-cool host star having seven known Earth-size planets will be a prime target for atmospheric characterization with JWST. However, the detectability of atmospheric molecular species may be severely impacted by the presence of clouds and/or hazes. In this work, we perform 3-D General Circulation Model (GCM) simulations with the LMD Generic model supplemented by 1-D photochemistry simulations at the terminator with the Atmos model to simulate several possible atmospheres for TRAPPIST-1e, 1f and 1g: 1) modern Earth, 2) Archean Earth, and 3) CO2-rich atmospheres. JWST synthetic transit spectra were computed using the GSFC Planetary Spectrum Generator (PSG). We find that TRAPPIST-1e, 1f and 1g atmospheres, with clouds and/or hazes, could be detected using JWST's NIRSpec prism from the CO2 absorption line at 4.3 um in less than 15 transits at 3 sigma or less than 35 transits at 5 sigma. However, our analysis suggests that other gases would require hundreds (or thousands) of transits to be detectable. We also find that H2O, mostly confined in the lower atmosphere, is very challenging to detect for these planets or similar systems if the planets' atmospheres are not in a moist greenhouse state. This result demonstrates that the use of GCMs, self-consistently taking into account the effect of clouds and sub-saturation, is crucial to evaluate the detectability of atmospheric molecules of interest as well as for interpreting future detections in a more global (and thus robust and relevant) approach.

Radio-loud AGN in the first LoTSS data release. The lifetimes and environmental impact of jet-driven sources

Abstract: We constructed a sample of 23 344 radio-loud active galactic nuclei (RLAGN) from the catalogue derived from the LOFAR Two-Metre Sky Survey (LoTSS) survey of the HETDEX Spring field. Although separating AGN from star-forming galaxies remains challenging, the combination of spectroscopic and photometric techniques we used gives us one of the largest available samples of candidate RLAGN. We used the sample, combined with recently developed analytical models, to investigate the lifetime distribution of RLAGN. We show that large or giant powerful RLAGN are probably the old tail of the general RLAGN population, but that the low-luminosity RLAGN candidates in our sample, many of which have sizes < 100 kpc, either require a very different lifetime distribution or have different jet physics from the more powerful objects. We then used analytical models to develop a method of estimating jet kinetic powers for our candidate objects and constructed a jet kinetic luminosity function based on these estimates. These values can be compared to observational quantities, such as the integrated radiative luminosity of groups and clusters, and to the predictions from models of RLAGN feedback in galaxy formation and evolution. In particular, we show that RLAGN in the local Universe are able to supply all the energy required per comoving unit volume to counterbalance X-ray radiative losses from groups and clusters and thus prevent the hot gas from cooling. Our computation of the kinetic luminosity density of local RLAGN is in good agreement with other recent observational estimates and with models of galaxy formation.

Control of the Exciton Radiative Lifetime in van der Waals Heterostructures.

Abstract: Optical properties of atomically thin transition metal dichalcogenides are controlled by robust excitons characterized by a very large oscillator strengths. Encapsulation of monolayers such as ${\mathrm{MoSe}}_{2}$ in hexagonal boron nitride (hBN) yields narrow optical transitions approaching the homogenous exciton linewidth. We demonstrate that the exciton radiative rate in these van der Waals heterostructures can be tailored by a simple change of the hBN encapsulation layer thickness as a consequence of the Purcell effect. The time-resolved photoluminescence measurements show that the neutral exciton spontaneous emission time can be tuned by one order of magnitude depending on the thickness of the surrounding hBN layers. The inhibition of the radiative recombination can yield spontaneous emission time up to 10 ps. These results are in very good agreement with the calculated recombination rate in the weak exciton-photon coupling regime. The analysis shows that we are also able to observe a sizable enhancement of the exciton radiative decay rate. Understanding the role of these electrodynamical effects allows us to elucidate the complex dynamics of relaxation and recombination for both neutral and charged excitons.

Simulating an isolated dwarf galaxy with multichannel feedback and chemical yields from individual stars

Abstract: In order to better understand the relationship between feedback and galactic chemical evolution, we have developed a new model for stellar feedback at grid resolutions of only a few parsecs in global disk simulations, using the adaptive mesh refinement hydrodynamics code Enzo. For the first time in galaxy scale simulations, we simulate detailed stellar feedback from individual stars including asymptotic giant branch winds, photoelectric heating, Lyman-Werner radiation, ionizing radiation tracked through an adaptive ray-tracing radiative transfer method, and core collapse and Type Ia supernovae. We furthermore follow the star-by-star chemical yields using tracer fields for 15 metal species: C, N, O, Na, Mg, Si, S, Ca, Mn, Fe, Ni, As, Sr, Y, and Ba. We include the yields ejected in massive stellar winds, but greatly reduce the winds' velocities due to computational constraints. We describe these methods in detail in this work and present the first results from 500~Myr of evolution of an isolated dwarf galaxy with properties similar to a Local Group, low-mass dwarf galaxy. We demonstrate that our physics and feedback model is capable of producing a dwarf galaxy whose evolution is consistent with observations in both the Kennicutt-Schmidt relationship and extended Schmidt relationship. Effective feedback drives outflows with a greater metallicity than the ISM, leading to low metal retention fractions consistent with observations. Finally, we demonstrate that these simulations yield valuable information on the variation in mixing behavior of individual metal species within the multi-phase interstellar medium.

High-energy behavior of strong-field QED in an intense plane wave

Abstract: Analytical calculations of radiative corrections in strong-field QED have hinted that in the presence of an intense plane wave the effective coupling of the theory in the high-energy sector may increase as the ($2/3$)-power of the energy scale. These findings have raised the question of their compatibility with the corresponding logarithmic increase of radiative corrections in QED in vacuum. However, all these analytical results in strong-field QED have been obtained within the limiting case of a background constant crossed field. Starting from the polarization operator and the mass operator in a general plane wave, we show that the constant-crossed-field limit and the high-energy limit do not commute with each other and identify the physical parameter discriminating between the two alternative limits orders. As a result, we find that the power-law scaling at asymptotically large energy scales pertains strictly speaking only to the case of a constant crossed background field, whereas high-energy radiative corrections in a general plane wave depend logarithmically on the energy scale as in vacuum. However, we also confirm the possibility of testing the ``power-law'' regime experimentally by means of realistic setups involving, e.g., high-power lasers or high-density electron-positron bunches.

Gas versus dust sizes of protoplanetary discs: effects of dust evolution

Abstract: Context. The extent of the gas in protoplanetary discs is observed to be universally larger than the extent of the dust. This is often attributed to radial drift and grain growth of the millimetre grains, but line optical depth produces a similar observational signature.Aims. We investigate in which parts of the disc structure parameter space dust evolution and line optical depth are the dominant drivers of the observed gas and dust size difference.Methods. Using the thermochemical model DALI with dust evolution included we ran a grid of models aimed at reproducing the observed gas and dust size dichotomy.Results. The relation between R dust and dust evolution is non-monotonic and depends on the disc structure. The quantity R gas is directly related to the radius where the CO column density drops below 1015 cm−2 and CO becomes photodissociated; R gas is not affected by dust evolution but scales with the total CO content of the disc. While these cases are rare in current observations, R gas /R dust > 4 is a clear sign of dust evolution and radial drift in discs. For discs with a smaller R gas /R dust , identifying dust evolution from R gas /R dust requires modelling the disc structure including the total CO content. To minimize the uncertainties due to observational factors requires FWHMbeam 10 on the 12 CO emission moment zero map. For the dust outer radius to enclose most of the disc mass, it should be defined using a high fraction (90–95%) of the total flux. For the gas, any radius enclosing >60% of the 12 CO flux contains most of the disc mass.Conclusions. To distinguish radial drift and grain growth from line optical depth effects based on size ratios requires discs to be observed at high enough angular resolution and the disc structure should to be modelled to account for the total CO content of the disc.

Ocean Dynamics and the Inner Edge of the Habitable Zone for Tidally Locked Terrestrial Planets

Abstract: National Science Foundation of China (NSFC) [41861124002, 41675071, 41606060, 41761144072]; NSFC [41375072, 41530423]

Global Simulations of Protoplanetary Disk Outflows with Coupled Non-ideal Magnetohydrodynamics and Consistent Thermochemistry

Abstract: Magnetized winds may be important in dispersing protoplanetary disks and influencing planet formation. We carry out global full magnetohydrodynamic simulations in axisymmetry, coupled with ray-tracing radiative transfer, consistent thermochemistry, and non-ideal MHD diffusivities. Magnetized models lacking EUV photons ($h u>13.6\ \mathrm{eV}$) feature warm molecular outflows that have typical poloidal speeds $\gtrsim 4\ \mathrm{km\ s}^{-1}$. When the magnetization is sufficient to drive accretion rates $\sim 10^{-8}\ M_\odot\ \mathrm{yr}^{-1}$, the wind mass-loss rate is comparable. Such outflows are driven not centrifugally but by the pressure of toroidal magnetic fields produced by bending the poloidal field. Both the accretion and outflow rates increase with the poloidal field energy density, the former almost linearly. The mass-loss rate is also strongly affected by ionization due to UV and X-ray radiation near the wind base. Adding EUV irradiation to the system heats, ionizes, and accelerates the part of the outflow nearest the symmetry axis, but reduces the overall mass-loss rate by exerting pressure on the wind base. Most of our models are non-turbulent, but some with reduced dust abundance and therefore higher ionization fractions exhibit magnetorotational instabilities near the base of the wind.

Self-luminous and Irradiated Exoplanetary Atmospheres Explored with HELIOS

Abstract: We present new methodological features and physical ingredients included in the 1D radiative transfer code HELIOS, improving the hemispheric two-stream formalism. We conduct a thorough intercomparison survey with several established forward models, including COOLTLUSTY, PHOENIX, and find satisfactory consistency with their results. Then, we explore the impact of (i) different groups of opacity sources, (ii) a stellar path length adjustment, and (iii) a scattering correction on self-consistently calculated atmospheric temperatures and planetary emission spectra. First, we observe that temperature-pressure (T-P) profiles are very sensitive to the opacities included, with metal oxides, hydrides, the alkali atoms (and ionized hydrogen) playing an important role for the absorption of shortwave radiation (in very hot surroundings). Moreover, if these species are sufficiently abundant, they are likely to induce non-monotonic T-P profiles. Second, without the stellar path length adjustment, the incoming stellar flux is significantly underestimated for zenith angles above 80°, which somewhat affects the upper atmospheric temperatures and the planetary emission. Third, the scattering correction improves the accuracy of the computation of the reflected stellar light by ~10%. We use HELIOS to calculate a grid of cloud-free atmospheres in radiative-convective equilibrium for self-luminous planets for a range of effective temperatures, surface gravities, metallicities, and C/O ratios, to be used by planetary evolution studies. Furthermore, we calculate dayside temperatures and secondary eclipse spectra for a sample of exoplanets for varying chemistry and heat redistribution. These results may be used to make predictions on the feasibility of atmospheric characterizations with future observations.