Blackbody Distribution Research Articles

Spectral distortions from promising single and multifield inflationary models

Forthcoming missions probing the absolute intensity of the CMB are expected to be able to measurespectral distortions, which are deviations from its blackbody distribution. As cosmic inflation can induce spectraldistortions, these experiments offer a possibility to further test the various promising inflationaryproposals, whose predictions need to be carefully determined. After numerically fitting all inflationaryobservables to match current observations, we compute the predicted spectral distortions ofvarious promising single and multifield inflationary models. The predictions of single-fieldinflationary models display deviations between 0.5% and 20% with respect to the standard cosmologicalmodel in the observable window, where multi-natural and axion-monodromy inflation stand out in this respect.In the case of multifield inflation, we observe a richer structure of the power spectrum, which, inthe case of so-called hybrid attractors, yields spectral distortions about 100 times more intense thanthe standard signal. These observations open up questions about the relation among our resultsand other cosmological observables that are also to be probed soon, such as the production ofprimordial black holes and gravitational waves.

Towards inferring the geometry of kilonovae

ABSTRACT Recent analysis of the kilonova, AT2017gfo, has indicated that this event was highly spherical. This may challenge hydrodynamics simulations of binary neutron star mergers, which usually predict a range of asymmetries, and radiative transfer simulations show a strong direction dependence. Here we investigate whether the synthetic spectra from a 3D kilonova simulation of asymmetric ejecta from a hydrodynamical merger simulation can be compatible with the observational constraints, suggesting a high degree of sphericity in AT2017gfo. Specifically, we determine whether fitting a simple P-Cygni line profile model leads to a value for the photospheric velocity that is consistent with the value obtained from the expanding photosphere method. We would infer that our kilonova simulation is highly spherical at early times, when the spectra resemble a blackbody distribution. The two independently inferred photospheric velocities can be very similar, implying a high degree of sphericity, which can be as spherical as inferred for AT2017gfo, demonstrating that the photosphere can appear spherical even for asymmetrical ejecta. The last-interaction velocities of radiation escaping the simulation show a high degree of sphericity, supporting the inferred symmetry of the photosphere. We find that when the synthetic spectra resemble a blackbody, the expanding photosphere method can be used to obtain an accurate luminosity distance (within 4–7 per cent).

Application of absorption-line blackbody distribution functions for H2O-CO2 mixtures for the spectral integration of the radiative transfer equation with the SLW model

This study presents the generation and evaluation of absorption-line blackbody distribution functions for mixtures (ALBDF-M) of CO2 and H2O. These functions are employed in the spectral integration of the radiative transfer equation in the framework of the spectral line-based weighted-sum-of-gray-gases (SLW) model. The proposed approach avoids the need to model the mixture of gases when dealing with ALBDFs obtained for pure H2O and CO2 species, which is the methodology currently adopted in the SLW literature. The ALBDF-M can be used with any development of the SLW model to manage local variations of the thermodynamic state conditions. In the present study, both the rank (RC-) and the locally correlated (LC-) SLW methodologies are employed with the ALBDF-M for an uncouple solution of an axisymmetric field that is representative of the combustion of ethylene diluted with H2O. Comparisons with line-by-line (LBL) solutions show that using the ALBDF-M provides an improvement in the accuracy when compared to the standard methodology to combine the ALBDFs generated for CO2 and H2O individually.

On Wien’s peaks

Most Modern Physics Books contain a chapter on the Laws of Black Body radiation when introducing the principles of Quantum Mechanics. These laws govern many phenomena that we encounter in daily life, technological developments, and scientific research. For that, this old subject is still of great importance, and even now some issues require our attention. This work addresses one of these topics. We describe why it has no sense to think that the wavelength at which Planck’s black-body spectral radiance distribution plotted as a function of the wavelength has its maximum value, must be the same that the wavelength calculated from the peak value obtained when the distribution is plotted as a function of another variable, such as the energy of the photons. We will show how the issue lies in using the correct form to calculate this wavelength from measured quantities.

SN 2023ixf in Messier 101: A Variable Red Supergiant as the Progenitor Candidate to a Type II Supernova

We present preexplosion optical and infrared (IR) imaging at the site of the type II supernova (SN II) 2023ixf in Messier 101 at 6.9 Mpc. We astrometrically registered a ground-based image of SN 2023ixf to archival Hubble Space Telescope (HST), Spitzer Space Telescope (Spitzer), and ground-based near-IR images. A single point source is detected at a position consistent with the SN at wavelengths ranging from HST R band to Spitzer 4.5 μm. Fitting with blackbody and red supergiant (RSG) spectral energy distributions (SEDs), we find that the source is anomalously cool with a significant mid-IR excess. We interpret this SED as reprocessed emission in a 8600 R ⊙ circumstellar shell of dusty material with a mass ∼5 × 10−5 M ⊙ surrounding a and K RSG. This luminosity is consistent with RSG models of initial mass 11 M ⊙, depending on assumptions of rotation and overshooting. In addition, the counterpart was significantly variable in preexplosion Spitzer 3.6 and 4.5 μm imaging, exhibiting ∼70% variability in both bands correlated across 9 yr and 29 epochs of imaging. The variations appear to have a timescale of 2.8 yr, which is consistent with κ-mechanism pulsations observed in RSGs, albeit with a much larger amplitude than RSGs such as α Orionis (Betelgeuse).

Simulation of edge effects in thermophotovoltaic efficiency by Monte Carlo calculation

Thermophotovoltaic (TPV) is one of the efficient ways that convert heat to electricity. The high-temperature emitter emits infrared photons omnidirectionally, and the view factor would be very larger compared with photovoltaic. This means that the effect of non-normal incidence will be very significant. In this work, we constructed a four-layer model consisting of the reflector, filter, anti-reflection-coating, and TPV cell. Based on the Monte Carlo algorithm, randomly generated photons that obey the black-body radiation distribution law on the surface of the emitter were tracked, and finally, the reached positions on the TPV cell were recorded. Calculations show that the density of photons received at the edge of the TPV is significantly less and depends on the interlayer spacing. We also analyzed the perimeter effect in the two-dimensional situation and gave possible optimization strategies.

Exploring the intra-4f and the bright white light upconversion emissions of Gd2O3:Yb3+,Er3+-based materials for thermometry.

Upconversion broadband white light emission driven by low-power near-infrared (NIR) lasers has been reported for many materials, but the mechanisms and effects related to this phenomenon remain unclear. Herein, we investigate the origin of laser-induced continuous white light emission in synthesized nanoparticles (Gd0.89Yb0.10Er0.01)2O3 and a mechanical mixture of commercial oxides with the same composition 89% Gd2O3, 10% Yb2O3, and 1% Er2O3. We report their photophysical features with respect to sample compactness, laser irradiation (wavelength, power density, excitation cycles), pressure, temperature, and temporal dynamics. Despite the sensitizer (Yb3+) and activator (Er3+) being in different particles for the mechanical mixture, efficient discrete and continuous upconversion emissions were observed. Furthermore, the synthesized nanoparticles were developed as primary luminescent thermometers (upon excitation at NIR) in the 299-363 K range, using the Er3+ upconversion 2H11/2 → 4I15/2/4S3/2 → 4I15/2 intensity ratio. They were also operating as secondary ones in the 1949-3086 K, based on the blackbody distribution of the observed white light emission. Our findings provide important insights into the mechanisms and effects related to the transition from discrete to continuous upconversion emissions with potential applications in remote temperature sensing.

The ω-absorption line distribution function for rank correlated SLW model prediction of radiative transfer in non-uniform gases

Unlike previous global methods, the recently developed Rank Correlated Spectral Line Weighted-sum-of-gray-gases (RC-SLW) model does not require specification of a reference gas thermodynamic state from which all other states are corrected using a correlated spectrum assumption. However, the RC-SLW approach still requires specification of an arbitrary blackbody source temperature to generate the Absorption Line Blackbody Distribution Function (ALBDF) used in construction of the spectral model. This paper reports on the development of a universal RC-SLW model that eliminates the need for the specification of a blackbody source temperature. The approach replaces the ALBDF with a new spectral distribution function, herein termed the ω-Absorption Line Distribution Function (ω-ALDF), and is based on a new spectral weighting function instead of the Planck blackbody distribution function. The ω-ALDF presented here depends only on the local gas thermodynamic state, and does not involve the blackbody source temperature used in the ALBDF. The new weighting function is determined using the well-established ALBDF, avoiding the need to generate a radically new distribution function database from the detailed gas absorption cross-section data. The ω-ALDF based RC-SLW model thus requires no user-specified parameters (no reference thermodynamic state and no blackbody source temperature). Further, only minor modification of the conventional RC-SLW model is needed to implement the new approach. Development of this new distribution function is only possible within the theoretical framework of the Rank Correlated SLW model. This work presents the theoretical development of the ω-ALDF, and demonstrates the use and accuracy of this new universal RC-SLW model.

A new infrared photometric study of hydrogen-deficient carbon stars, R CrB stars and extreme helium stars in our galaxy

We have collected almost all HdC, RCB and EHe stars up to date to investigate their infrared properties, in particular, their radiation mechanisms in the infrared, using the observational data from 2MASS, WISE and IRAS missions. Because HdC stars, RCB stars and EHe stars all belong to the category of extremely hydrogen-deficient stars and they definitely have some evolutionary connections.It is found from this paper that all RCB stars have infrared excesse in the wavelength region from the near infrared to the far infrared covered by 2MASS, WISE and IRAS due to dust while almost all HdC stars and EHe stars have no or little infrared excess.From 2MASS, WISE and IRAS two-color diagrams, it is also found that the majority of these three kinds of stars are around the power law distributions in the near infrared possibly indicative of their infrared radiations from the warm dust in the disk-like envelope. It is also found that in the mid- and far infrared regions some stars are around the power law distribution perhaps due to dust from disk-like envelope while some stars are around the blackbody distribution maybe due to the cold and extended nebulosity nearby.

A new photometric study of B[e] stars in the infrared

Abstract We have collected almost all B[e] stars (120 stars in total) listed in the literature up to the present time. We have then photometrically studied their infrared properties by using data from IRAS, WISE, and 2MASS. From several two-color diagrams we found that infrared radiation for the majority of B[e] stars shows a power law distribution from dusty/gaseous circumstellar disks in the 1–60 μm region. We also found that, possibly due to the influence of polycyclic aromatic hydrocarbon and silicate emissions, some B[e] stars have a blackbody distribution in the 3–12 μm region, and due to the influence of clouds/nebulae nearby some B[e] stars also show blackbody distributions in the IRAS wavelengths. Furthermore, we compared infrared properties between B[e] stars and Be stars, and between B[e] stars and HAeBe stars. We show that the infrared excess of B[e] stars is much larger than for Be stars in the 1–25 μm region, while both B[e] and HAeBe stars have similar infrared color properties in the 1–25 μm region.

WISE observations for the variety of Galactic carbon stars

WISE observations of visual carbon stars (VCSs), infrared carbon stars (IRCSs), extreme carbon stars (ECSs), J-type carbon stars JCSs), and silicate carbon stars (SCSs) are presented in this paper. We found that in the WISE observational region carbon stars still form a sequence of VCSs → IRCSs → ECSs with the color gradually increasing. We also found that in the WISE two-color diagrams the JCS distribution is similar to that for the VCS, while the ECS distribution is similar to the IRCS. In addition, most of these carbon stars are around or on the lower right side of blackbody distributions in the WISE two-color diagrams due to the thermal radiation from dusty circumstellar envelopes, while some of them are around or on the upper left side of power law distributions possibly due to the radiation from dusty disks or showing the influence from some molecular features.

Efficient SLW models for water vapor and carbon dioxide based on neural network method

Non-gray gas radiation plays an important role in combustion system, and the spectral-line-based weighted-sum-of-gray-gases (SLW) is a popular model to treat the gas radiative properties. In practical applications, the inverse calculations of the cross-sections from a specified F are time demanding. The neural network method is used here to develop inverse absorption line blackbody distribution function (ALBDF) to efficiently and accurately calculate the cross-sections from F. Results show that the neural network based SLW can predict the inverse ALBDF very well and the relative errors for the radiative heat source and heat flux for the radiation transfer are less than 2%. The computational time of the neural network based SLW is only 1/10th of the original SLW model.

Plasma temperature measurements using black-body radiation from spectral lines emitted by a capillary discharge

Optically thick spectral line emssion from plasmas is often difficult to use for the diagnosis of plasma parameters. We demonstrate a technique for temperature measurement using the peak intensity of optically thick lines as their intensities approach a black-body distribution. Recording optical emission in the wavelength range 300–1000 nm from a plasma formed by radio-frequency heating and electrical discharges in a 0.2 m long capillary plasma, we show that the high wavelength Rayleigh-Jeans form of the black-body emission can be fitted to the most intense spectral lines to give a measurement of plasma temperatures in the 1–1.5 eV range. The temperature measurement technique should have wider applicability in diagnosing plasmas with optically thick spectral lines.

An exploration of the influence of spectral model parameters on the accuracy of the rank correlated SLW model

This paper explores the influence of spectral model parameters on the accuracy of the Rank Correlated Spectral Line Weighted-sum-of-gray-gases (RC-SLW) model. The range of the Absorption Line Blackbody Distribution Function (ALBDF) database has been extended as part of this work, and the range of the ALBDF database has been studied as it relates to the RC-SLW model construction and prediction accuracy. The study first defines the maximum lower limit of the absorption cross-section in the ALBDF database which produces accurate predictions of total emissivity. It is shown that although the RC-SLW method yields very good accuracy, results may exhibit some sensitivity to the method used to specify the quadrature bounds. The critical need for sufficiently broad ALBDF data is demonstrated. Complete independence of predictions on blackbody source temperature is demonstrated, provided the solution is accurately numerically resolved. Finally, it is shown that accurate predictions may be achieved using the RC-SLW model using just a few gray gases.

Dual-band quasi-coherent radiative thermal source

Thermal radiation from an unpatterned object is similar to that of a gray body. The thermal emission is insensitive to polarization, shows only Lambertian angular dependence, and is well modeled as the product of the blackbody distribution and a scalar emissivity over large frequency bands. Here, we design, fabricate and experimentally characterize the spectral, polarization, angular and temperature dependence of a microstructured SiC dual band thermal infrared source; achieving independent control of the frequency and polarization of thermal radiation in two spectral bands. The measured emission of the device in the Reststrahlen band (10.3–12.7 µm) selectively approaches that of a blackbody, peaking at an emissivity of 0.85 at λx=11.75μm and 0.81 at λy=12.25μm. This effect arises due to the thermally excited phonon polaritons in silicon carbide. The control of thermal emission properties exhibited by the design is well suited for applications requiring infrared sources, gas or temperature sensors and nanoscale heat transfer. Our work paves the way for future silicon carbide based thermal metasurfaces.

Dynamics of Surface Streamer Plasmas at Atmospheric Pressure: Mixtures of Argon and Methane

A nonequilibrium atmospheric streamer discharge was investigated as a means to seed a large-gap arc breakdown. The dynamics of the streamer were analyzed with high speed imaging, photodiode light intensity, and current–voltage measurements. The temporal evolution of the discharge included a localized surface corona and a positive surface streamer. With the addition of an impurity gas (methane), the ionization was suppressed, which inhibited surface streamer propagation. The electron temperature was determined from time and spatially averaged spectra, coupled with a collisional–radiative model. The electron temperature in argon was measured at 1.25 eV for an electron density range of 1019 – 1020 m –3. Partial local thermodynamic equilibrium calculations showed that the Ar II 4p states followed a Boltzmann distribution with an excitation temperature of 0.7 eV. The gas temperature was estimated at 815 K from a black-body distribution. The velocity of the surface streamer in argon was estimated at ~100 km/s with a diameter of $\sim 500~\mu \text{m}$ .

The rank correlated SLW model of gas radiation in non-uniform media

A comprehensive theoretical development of possible reference approaches in modelling of radiation transfer in non-uniform gaseous media is developed within the framework of the Generalized SLW Model. The notion of absorption spectrum “correlation” adopted currently for global methods in gas radiation is critically revisited and replaced by a less restrictive concept of rank correlated spectrum. Within this framework it is shown that eight different reference approaches are possible, of which only three have been reported in the literature. Among the approaches presented is a novel Rank Correlated SLW Model, which is distinguished by the fact that i) it does not require the specification of a reference gas thermodynamic state, and ii) it preserves the emission term in the spectrally integrated Radiative Transfer Equation. Construction of this reference model requires only two absorption line blackbody distribution functions, and subdivision into gray gases can be performed using standard quadratures. Consequently, this new reference approach appears to have significant advantages over all other methods, and is, in general, a significant improvement in the global modelling of gas radiation. All reference approaches are summarized in the present work, and their use in radiative transfer prediction is demonstrated for simple example cases. Further, a detailed rigorous theoretical development of the improved methods is provided.

HOT ELECTROMAGNETIC OUTFLOWS. III. DISPLACED FIREBALL IN A STRONG MAGNETIC FIELD

The evolution of a dilute electron-positron fireball is calculated in the regime of strong magnetization and very high compactness (l ~10^3-10^8). Heating is applied at a low effective temperature (< 25 keV), and the fireball is allowed to expand, so that the formation of a black-body spectral distribution is inhibited by pair annihilation. The diffusion equation for Compton scattering is coupled to a single-temperature pair gas and an exact (trans-relativistic) cyclo-synchrotron photon source. We find that the photon spectrum develops a quasi-thermal peak, with a power-law slope below it that is characteristic of gamma-ray bursts. The formation of a thermal high-frequency spectrum is checked using the full kinetic equations at l ~ 10^3. These results have several implications for the central engine of GRBs, and the mechanism of energy transport. 1. Baryon rest mass carries less than ~ 10^{-5} of the energy flux at jet breakout inside ~ 10^{12} cm from the engine, with most carried by the magnetic field. 2. This degree of baryon purity points to the presence of an event horizon in the engine, and neutrons play a negligible role in the prompt emission mechanism. 3. X-ray flashes are emitted by outflows carrying enough baryons that the photosphere is pair-depleted, which we show results in faster thermalization. 4. The relation between observed peak frequency and burst luminosity is bounded below by the observed Amati et al. relation if jet Lorentz factor ~ 1/(opening angle) at breakout. 5. Stellar models are used to demonstrate an inconsistency between the highest observed GRB energies, and a hydrodynamic nozzle: magnetic collimation is required. 6. The magnetized pair gas is dilute enough that high-frequency Alfven waves may become charge starved. Finally, we suggest that limitations on magnetic reconnection from plasma collisionality have been overestimated.

Absorption line black body distribution function evaluated with proper orthogonal decomposition for mixture of CO2 and H2O

Purpose – The purpose of this paper is to present a new approach of evaluation of the absorption line black body distribution function (ALBDF) for a mixture of gases. Currently published correlations, which are used to reproduce the ALBDF, treat only single gases. Design/methodology/approach – A discrete form of the ALBDF is generated using line by line (LBL) calculations. The latest spectroscopic database HITEMP 2010 is used for the generation of the absorption coefficient histogram, which is cumulated later in order to produce a tabulated form of the ALBDF. The proper orthogonal decomposition (POD) statistical method is employed for the reproduction of the ALBDF. Interpolation property of the POD allows to reproduce the ALBDF for arbitrary gas mixture parameters. Findings – POD proved to possess optimal interpolation properties. Results obtained by using POD are in very good agreement with LBL integration. Research limitations/implications – One have to be aware that the model generated with the POD method can be used only within the range of parameters used to build the model. The POD does not perform any property extrapolation. The model is limited to a mixture of two gases, namely CO2 and H2O. Expanding the number of gases used in the mixture may lead to a relatively large matrix system, which is difficult to process with the POD approach. Practical implications – The presented approach can be used to produce absorption coefficients values and their weights, which can be applied in the gas radiative properties description using the weighted sum of gray gas (WSGG) concept. The proposed model can be used with any radiative transfer equation solver which employs the WSGG approach. Originality/value – For the first time, radiative properties of gas mixtures are reproduced using the POD approach.

Efficient representation of the absorption line blackbody distribution function for H2O, CO2, and CO at variable temperature, mole fraction, and total pressure

The absorption line blackbody distribution function (ALBDF) is the primary tool used in the SLW model for calculating the weights of gray gases. The ALBDF for H2O, CO2, and CO is calculated rigorously using the HITEMP 2010 spectroscopic database. The line-by-line data is the basis for an updated and improved hyperbolic tangent correlation of the ALBDF, valid for temperatures ranging from 400K to 3000K and total pressures ranging from 0.1atm to 50atm. The correlations are first established at atmospheric pressure, and variable total pressure is accounted for as a shift from the atmospheric pressure calculation. Further, the line-by-line ALBDF data have been tabulated to directly represent the ALBDF; the ALBDF has been tabulated for discrete temperatures ranging from 300K to 3000K, mole fractions (where appropriate) from 0 to 1, and total pressures ranging from 0.1atm to 50atm. The data have been made available on the website http://albdf.byu.edu. Improvements made compared to other representations of the ALBDF include more rigorous generation of the detailed spectral absorption cross-section, correlation and tabulation of the ALBDF for CO, expansion to variable total pressure, and a higher temperature ceiling. The accuracy of the hyperbolic tangent correlation is characterized and regimes of relative lower accuracy identified, and it is demonstrated to be sufficiently accurate for engineering applications. The tabulated ALBDF data, which can be used directly in place of the correlation, are shown to be considerably more accurate than the correlation. There is an initial computational cost to read the tabulated data after which interpolation is used to obtain the ALBDF at specified conditions.The updated and expanded ALBDF correlation and the tabulated ALBDF data are used to compute total emissivity and radiative transfer in both homogeneous, isothermal media and non-homogeneous, non-isothermal media and are compared to line-by-line benchmark calculations. The hyperbolic tangent correlation performs very well in these calculations and shows excellent accuracy, while the accuracy of calculations using the tabulated data is considerably better.