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1.
The coupled set of equations of hydrodynamics and radiative transfer is derived for small disturbances in a plane, grey atmosphere. Only radiative transfer is taken into account in the energy equation; dynamical effects of radiation are ignored. A mean stationary radiative flux through the photosphere is taken into account. The radiative transfer equation is used by assuming the Eddington approximation, moreover, an exponential height profile of the temperature and an analytical opacity formula are supposed. For this model we obtained an asymptotic solution for plane nonadiabatic acoustic waves and radiation waves. The approach provides a detailed discussion of the interaction of nonadiabatic p‐modes and radiation waves in a realistic model of the photosphere of a solar‐like star.  相似文献   

2.
We investigate the effect of dust on the scaling properties of galaxy clusters based on hydrodynamic N -body simulations of structure formation. We have simulated five dust models plus radiative cooling and adiabatic models using the same initial conditions for all runs. The numerical implementation of dust was based on the analytical computations of Montier & Giard. We set up dust simulations to cover different combinations of dust parameters that make evident the effects of size and abundance of dust grains. Comparing our radiative plus dust cooling runs with a purely radiative cooling simulation, we find that dust has an impact on cluster scaling relations. It mainly affects the normalization of the scalings (and their evolution), whereas it introduces no significant differences in their slopes. The strength of the effect critically depends on the dust abundance and grain size parameters as well as on the cluster scaling. Indeed, cooling due to dust is effective in the cluster regime and has a stronger effect on the 'baryon driven' statistical properties of clusters such as   L X– M , Y – M , S – M   scaling relations. Major differences, relative to the radiative cooling model, are as high as 25 per cent for the   L X– M   normalization, and about 10 per cent for the Y – M and S – M normalizations at redshift zero. On the other hand, we find that dust has almost no impact on the 'dark matter driven'   T mw– M   scaling relation. The effects are found to be dependent in equal parts on both dust abundances and grain size distributions for the scalings investigated in this paper. Higher dust abundances and smaller grain sizes cause larger departures from the radiative cooling (i.e. with no dust) model.  相似文献   

3.
Paul G. Lucey  Sarah K. Noble 《Icarus》2008,197(1):348-353
We compare laboratory measurements of the optical effects of nanophase iron on near-IR reflectance spectra of transparent silica gel infused with small iron particles [Noble, S.K., Pieters, C.M., Keller, L.P., 2007. Icarus 192, 629-642] with a radiative transfer model of the process [Hapke, B., 2001. J. Geophys. Res. 106 (E5), 10039-10074]. We find that the measurements exhibit reddening and darkening effects of nanophase (<50 nm) iron particles, a darkening effect of somewhat larger particles (>50 nm) and mixing effects of silica gel particles of varying total iron abundance. The radiative transfer model reproduces the effects of nanophase iron within the experimental uncertainties.  相似文献   

4.
By using the concept of an “equivalent radiative atmosphere” (ERA) we can obtain a reasonably correct representation of the greenhouse factor for a real atmosphere. This elementary model may then be used to estimate the temperature effects due to changes in the abundances of minor i.r. absorbers. This global-mean model also serves as a basis for extending the model to the zonal energy-balance type developed by Budyko and Sellers and treated analytically by North. With this simple modification of a radiative-equilibrium model, we can show that global heating has the more profound effect at higher latitudes. By requiring the relative humidity to remain constant, we show that the positive feedback in H2O opacity is comparable to the initial change in opacity due, say, to a change in CO2 content.  相似文献   

5.
The effect of variation of radiative efficiency on the growth of the black hole mass is discussed. In the process of accretion, the black hole's angular momentum varies, resulting in a variation of the radiative efficiency, and the growth of the black hole mass is thereby affected. For the exponential growth model of back holes and taking into account the effect of a varying radiative efficiency, the equation for the growth of the black hole mass is solved numerically. Compared to the model that assumes a constant radiative efficiency, the result indicates that variation of radiative efficiency has a marked, retarding effect on the growth of the black hole mass. This model can explain quantitatively some recent observational results.  相似文献   

6.
A method is presented to include irradiation effects in the modeling of over-contact binaries. The Roche potential is numerically modified in a way to account for mechanical effects of the mutual irradiation of the two binary components. The efficiency of radiative interaction is parametrized by means of the fraction of radiative over gravitational forces for each component of the binary. The modified Roche geometry is implemented as binary model in an eclipse light curve solution code, which is based on the general Wilson–Devinney scheme. As an example the method is applied to the early-type over-contact system V606 Cen.  相似文献   

7.
An accessible model for interstellar OH/H2O maser associations is presented. It can be classified into radiative pumping model. It can close the dynamical cycle of H2O and OH species, and can give an interpretation on interstellar OH/H2O associations. A reasonable scheme for both regeneration and destruction of interstellar H2O and OH molecules is argued. Our model has overcome the defects of former radiative models, and is compatible with astronomical conditions. It is shown that the rotational population of H2O and OH in these regions is much less affected by collisions than by radiation. Some experiments have confirmed our proposal.  相似文献   

8.
Validation of global numerical models of planetary atmospheres requires simulating images and spectra from the IR to UV spectral regions in order to compare them with remote observations. This paper describes Rassvet, a 3-D spherical-shell backward Monte Carlo radiative transfer model developed for such simulations. It utilizes a new methodology for calculating atmospheric brightness in scattered sunlight by introducing the concept of an “effective emission source”. This allows for the accumulation of the scattered contribution along the entire path of a ray and the calculation of the atmospheric radiation when both scattered sunlight and thermal emission contribute to the remote measurement - which was not possible in previous models. A “polychromatic” algorithm is extended for applications with the backward Monte Carlo method and implemented in the model. It allows for the calculation of radiative intensity for several wavelengths simultaneously, resulting in improved efficiency. The capabilities of the model are demonstrated by simulating remote measurements from the atmosphere of Io.  相似文献   

9.
We present temporal and spectral characteristics of X-ray flares observed from six late-type G–K active dwarfs (V368 Cep, XI Boo, IM Vir, V471 Tau, CC Eri and EP Eri) using data from observations with the XMM–Newton observatory. All the stars were found to be flaring frequently and altogether a total of 17 flares were detected above the 'quiescent' state X-ray emission which varied from 0.5 to  8.3 × 1029 erg s−1  . The largest flare was observed in a low-activity dwarf XI Boo with a decay time of 10 ks and ratio of peak flare luminosity to 'quiescent' state luminosity of 2. We have studied the spectral changes during the flares by using colour–colour diagram and by detailed spectral analysis during the temporal evolution of the flares. The exponential decay of the X-ray light curves, and time evolution of the plasma temperature and emission measure are similar to those observed in compact solar flares. We have derived the semiloop lengths of flares based on the hydrodynamic flare model. The size of the flaring loops is found to be less than the stellar radius. The hydrodynamic flare decay analysis indicates the presence of sustained heating during the decay of most flares.  相似文献   

10.
We examine empirical atmospheric structures that are consistent with enhanced white-light continuum emission in solar flares. This continuum can be produced either by hydrogen bound-free emission in an enhanced region in the upper chromosphere, or by H- emission in an enhanced region around the temperature minimum. In the former case, weak Paschen jumps in the spectrum will be present, with the spectrum being dominated by a strong Balmer continuum, while in the latter case the spectrum exhibits a weaker, flat enhancement over the entire visible spectrum.We find that when proper account is taken of radiative backwarming processes, the two enhanced atmospheric regions above are not independent, in that irradiation by Balmer continuum photons from the upper chromosphere creates sufficient heating around the temperature minimum to account for the temperature enhancements there. Thus the problem of main phase white-light flare production reduces to one of creating temperature enhancements of order 104 K in the upper chromosphere; radiative backwarming then naturally accounts for the enhancements of order 100 K around the temperature minimum.Heating by electron and proton bombardment, and by XUV irradiation from above, are then considered as candidates for creating the necessary enhancements in the upper chromosphere. We find that electron bombardment can be ruled out, whereas bombardment by protons in the few-MeV energy range is a viable candidate, but one without strong observational support. The XUV irradiation hypothesis is examined by incorporating it self-consistently into the PANDORA radiative transfer algorithm used to construct the empirical model atmospheres; we find that the introduction of XUV radiation, with flux and spectrum appropriate to white-light flare events, does indeed produce sufficient radiative heating in the upper chromosphere to balance the radiative losses associated with the required temperature enhancements.In summary, we find that the radiative coupling of (i) the upper chromosphere and temperature minimum regions (through Balmer continuum photons) and (ii) the transition region and upper chromosphere (through XUV photons) can account for white-light emission in solar flares.Presidential Young Investigator.  相似文献   

11.
Earlier models of compressible, rotating, and homogeneous ellipsoids with gas pressure are generalized to include the presence of radiation pressure. Under the assumptions of a linear velocity field of the fluid and a bounded ellipsoidal surface, the dynamical behaviour of these models can be described by ordinary differential equations. These equations are used to study the finite oscillations of massive radiative models with masses 10M and 30M in which the effects of radiation pressure are expected to be important.Models with two different degrees of equilibrium are chosen: an equilibrium (i.e., dynamically stable) model with an initial asymmetric inward velocity, and a nonequilibrium model with a nonequilibrium central temperature and which falls inwards from rest. For each of these two degrees of equilibrium, two initial configurations are considered: rotating spheroidal and nonrotating spherical models.From the numerical integration of the differential equations for these models, we obtain the time evolution of their principal semi-diametersa 1 anda 3, and of their central temperatures, which are graphically displayed by making plots of the trajectories in the (a 1,a 3) phase space, and of botha 1 and the total central pressureP c against time.It is found that in all the equilibrium radiative models (in which radiation pressure is taken into account), the periods of the oscillations of botha 1 andP c are longer than those of the corresponding nonradiative models, while the reverse is true for the nonequilibrium radiative models. The envelopes of thea 1 oscillations of the equilibrium radiative models also have much longer periods; this result also holds for the nonequilibrium models whenever the envelope is well defined. Further, as compared to the nonradiative models, almost all the radiative models collapse to smaller volumes before rebouncing, with the more massive model undergoing a larger collapse and attaining a correspondingly larger peakP c.When the mass is increased, the dynamical behavior of the radiative model generally becomes more nonperiodic. The ratio of the central radiation pressure to the central gas pressure, which is small for low mass models, increases with mass, and at the center of the more massive model, the radiation pressure can be comparable in magnitude to the gas pressure. In all the radiative models, the average periods as well as the average amplitudes of both thea 1 andP c oscillations also increase with mass.When either rotation or radiation pressure effects or both are included in the equilibrium nonradiative model, the period of the envelope of thea 1 oscillations is increased. The presence of rotation in the equilibrium radiative model, however, decreases this period.Some astrophysical implications of this work are briefly discussed.  相似文献   

12.
In the context of the unified model of Seyfert galaxies, we use observations from the literature and a radiative transfer model to investigate the near-IR to mm emission produced by the presumed torus in the Circinus galaxy, from 2 μm to 1.3 mm. From the infrared SED modelling, we find that the total luminosity ( L IR) in this wavelength range consists of similar contributions from the torus and starburst with a ratio of nuclear luminosity to starburst luminosity ( L NUC/ L SB)∼0.8 .
By using a similar torus model to that of NGC 1068, but without the conical dust , we find an upper limit to the outer torus radius of ∼12 pc with a best fit of ∼2 pc. The upper limit torus size estimated from the radiative transfer modelling is consistent with the 16-pc torus radius estimated from near-IR imaging polarimetry of Circinus.  相似文献   

13.
We present radiative transfer modelling of thermal emission from the nightside of Venus in two ‘spectral window’ regions at 1.51 and 1.55 μm. The first discovery of these windows, reported by Erard et al. [Erard, S., Drossart, P., Piccioni, G., 2009. J. Geophys. Res. Planets 114, doi:10.1029/2008JE003116. E00B27], was achieved using a principal component analysis of data from the VIRTIS instrument on Venus Express. These windows are spectrally narrow, with a full-width at half-maximum of ∼20 nm, and less bright than the well-known 1.7 and 2.3 μm spectral windows by two orders of magnitude.In this note we present the first radiative transfer analysis of these windows. We conclude that the radiation in these windows originates at an altitude of 20-35 km. As is the case for the other infrared window regions, the brightness of the windows is affected primarily by the optical depth of the overlying clouds; in addition, the 1.51 μm radiance shows a very weak sensitivity to water vapour abundance.  相似文献   

14.
We investigate the rotation profile of solar-like stars with magnetic fields. A diffu-sion coefficient of magnetic angular momentum transport is deduced. Rotating stellar models with different mass incorporating the coefficient are computed to give the rotation profiles. The total angular momentum of a solar model with only hydrodynamic instabilities is about 13 times larger than that of the Sun at the age of the Sun, and this model can not reproduce quasi-solid rotation in the radiative region. However, the solar model with magnetic fields not only can reproduce an almost uniform rotation in the radiative region, but also a total angular momentum that is consistent with the helioseismic result at the 3 σ level at the age of the Sun. The rotation of solar-like stars with magnetic fields is almost uniform in the radiative region, but for models of 1.2-1.5 M⊙, there is an obvious transition region between the convective core and the radiative region, where angular velocity has a sharp radial gradient, which is different from the rotation profile of the Sun and of massive stars with magnetic fields. The change of angular velocity in the transition region increases with increasing age and mass.  相似文献   

15.
We explore an accretion model for low luminosity AGN (LLAGN) that attributes the low radiative output to a low mass accretion rate, , rather than a low radiative efficiency. In this model, electrons are assumed to drain energy from the ions as a result of collisionless plasma microinstabilities. Consequently, the accreting gas collapses to form a geometrically thin disk at small radii and is able to cool before reaching the black hole. The accretion disk is not a standard disk, however, because the radial disk structure is modified by a magnetic torque which drives a jet and which is primarily responsible for angular momentum transport. We also include relativistic effects. We apply this model to the well known LLAGN M87 and calculate the combined disk-jet steady-state broadband spectrum. A comparison between predicted and observed spectra indicates that M87 may be a maximally spinning black hole accreting at a rate of ∼10−3 M ⊙ yr−1. This is about 6 orders of magnitude below the Eddington rate for the same radiative efficiency. Furthermore, the total jet power inferred by our model is in remarkably good agreement with the value independently deduced from observations of the M87 jet on kiloparsec scales.  相似文献   

16.
Solar variability is often cast in terms of radiative emission and the associated long-term climate response; however, growing societal reliance on technology is creating more interest in day-to-day solar variability. This variability is associated with both solar radiative and solar wind emissions. In this paper we explore the combined effects of radiative and solar wind fluctuations at Earth. The fluctuations in radiative and geomagnetic power create an extended interval of solar maximum for the upper atmosphere. We use a trio of empirical models to estimate, over the last three solar cycles, the relative contributions of solar extreme ultraviolet (UV) power, Joule power, and particle kinetic power to the Earth’s upper atmosphere energy budget. Daily power values are derived from three source models. The SOLAR2000 solar irradiance specification model provides estimates of the daily extreme and far UV solar power input. Geomagnetic power is derived from a combination of satellite-estimated particle precipitation power and an empirical model of Joule power from hemispherically integrated estimates of high-latitude energy deposition. During the interval 1975 to 2003, the average daily contributions were: particles – 36 GW, Joule – 95 GW and solar – 464 GW for a total of 595 GW. Solar wind-driven geomagnetic power provided 22% of the total global upper atmospheric energy. In the top 15 power events, geomagnetic power contributed two-thirds of the total power budget. In each of these events, Joule power alone exceeded solar power. With rising activity, Joule power becomes the most variable element of solar upper atmosphere interactions.  相似文献   

17.
A model representing the profile of the silicate absorption band at 9.8 μm in the spectra of BECKLIN -NEUGEBAUER objects has been developed, solving the equation of radiative transfer. The model based on the condition of radiative equilibrium, on an analytical temperature distribution and on the assumption of constant density in the circumstellar shell allows the evaluation of the optical depth in the band's centre and the investigation of the effect of the temperature variation at the inner boundary of the envelope. The optical depth in the band's centre ist calculated for the BN point source.  相似文献   

18.
Stephen D. Eckermann  Jun Ma 《Icarus》2011,211(1):429-442
Using a Curtis-matrix model of 15 μm CO2 radiative cooling rates for the martian atmosphere, we have computed vertical scale-dependent IR radiative damping rates from 0 to 200 km altitude over a broad band of vertical wavenumbers ∣m∣ = 2π(1-500 km)−1 for representative meteorological conditions at 40°N and average levels of solar activity and dust loading. In the middle atmosphere, infrared (IR) radiative damping rates increase with decreasing vertical scale and peak in excess of 30 days−1 at ∼50-80 km altitude, before gradually transitioning to scale-independent rates above ∼100 km due to breakdown of local thermodynamic equilibrium. We incorporate these computed IR radiative damping rates into a linear anelastic gravity-wave model to assess the impact of IR radiative damping, relative to wave breaking and molecular viscosity, in the dissipation of gravity-wave momentum flux. The model results indicate that IR radiative damping is the dominant process in dissipating gravity-wave momentum fluxes at ∼0-50 km altitude, and is the dominant process at all altitudes for gravity waves with vertical wavelengths ?10-15 km. Wave breaking becomes dominant at higher altitudes only for “fast” waves of short horizontal and long vertical wavelengths. Molecular viscosity plays a negligible role in overall momentum flux deposition. Our results provide compelling evidence that IR radiative damping is a major, and often dominant physical process controlling the dissipation of gravity-wave momentum fluxes on Mars, and therefore should be incorporated into future parameterizations of gravity-wave drag within Mars GCMs. Lookup tables for doing so, based on the current computations, are provided.  相似文献   

19.
John K. Hillier 《Icarus》1997,130(2):328-335
It has been proposed that composite particles containing internal scatterers may provide the explanation for the fact that most photometric studies of planetary surfaces based on Hapke's model of bidirectional reflectance have found the planetary particles to exhibit moderately backscattering phase functions. However, an implicit assumption made in this explanation is that the scattering by composite particles containing multiple internal inclusions in a planetary surface can still be adequately computed using standard radiative transfer theory assuming the composite particles to be the fundamental individual scatterers even though such particles are necessarily in close proximity to each other. In this paper, this assumption is explored by examining the effects of close packing on the light scattering by spherical particles containing isotropic internal scatterers using a Monte Carlo routine. As expected, classical radiative transfer (assuming a random distribution of scattering particles) coupled with the assumption that the composite particle is the fundamental scatterer provides a good approximation in the high porosity limit. However, even for porosities as high as 90% the effects of close packing are clearly seen with the radiative transfer calculation underestimating the scattering by ∼10% at high incidence, emission, and phase angles. As the porosity is lowered further, the discrepancy becomes more severe and can reach 50% or more. In contrast, assuming the individual scatterer properties in the radiative transfer calculation leads to a substantial overestimate of the scattering even for porosities as low as 27.5%. This suggests that parameters derived using the classical radiative transfer theory will yield results intermediate between those of the composite as a whole and those of the internal scatterers. Thus, one should exercise caution in interpreting the results of models based on classical radiative transfer theory in terms of the physical properties of the surface particles and, where possible, the bidirectional reflectance of densely packed composite particles should be computed using more accurate methods such as the stochastic radiative transfer theory.  相似文献   

20.
Thomas R. Hanley 《Icarus》2005,177(1):286-290
Laboratory measurements of the microwave opacity of HCl in a CO2 atmosphere have been conducted in the S (13.3 cm), X (3.6 cm), and K (1.4 cm) microwave bands at a pressure of 7.2 bar and at two different mixing ratios. The results are consistent with an opacity model employing the Van Vleck-Weisskopf lineshape applied to the published submillimeter line intensities of HCl (JPL Catalog [Pickett et al., 1998, J. Quant. Spectrosc. Rad. Trans. 60, 883-890]) and empirically fitted with a modeled parameter for CO2 broadening. Based on the deep atmospheric abundance of HCl inferred from near-infrared measurements [Dalton et al., 2000, Bull. Am. Astron. Soc. 32, 1120], the resulting modeled HCl opacity is constrained to have a small effect on the overall microwave absorption spectrum of Venus, but can be used in developing a more accurate radiative transfer model.  相似文献   

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