共查询到20条相似文献，搜索用时 701 毫秒
1.
Basil Petropoulos 《Earth, Moon, and Planets》1988,42(1):29-40
The following parameters have been computed for the Cytherean atmosphere: pressure, density, speed of sound, collisional frequency, column mass, density scale, mean-free-path, viscosity, pressure scale, mean particle velocity, number density at an altitude from 0 to 170 km.The chemical composition, the temperature distribution function of the altitude, the surface pressure and the surface temperature measured by Pioneer Venus have been used as input data for these computations. 相似文献
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Line intensity ratios of EUV emission lines from Navii and Alix have been considered for electron density and temperature determinations within the chromosphere-corona transition region and the corona. The electron pressure within the emission region has been assumed to be a constant parameter. Theoretical line intensities for these ions have been computed using a model solar atmosphere and compared with the values as observed by ATM ultraviolet spectrometer. The observed intensities correspond to the average quiet-Sun conditions near solar minimum. 相似文献
4.
Steady state level density of 20 levels of boron-like ions, Mg viii and Si x, have been computed as a function of electron density and temperature. We have accounted for collisional and spontaneous radiative processes. Photo-excitation between the two levels of the ground term has also been considered. Using the computed level density, line intensities have been obtained as a function of electron density and temperature. In case of Mg viii, line intensity ratio I(430.47)/I(436.62) is found to be electron density sensitive. Likewise other pairs of lines namely, I(75.03)/I(74.86), I(315.02)/I(430.47), and I(315.02)/I(335.23) are also found to be density sensitive. Similar density sensitive line intensity ratios have been found for Si x. Absolute line fluxes from these ions at earth distance have been computed and are found to be comparable with values obtained, using various satellite and rocket measurements.Paper presented at the 5th Astronomical Society of India Meeting, held at Uttar Pradesh State Observatory, Naini Tal, India, 5–9 November, 1979. 相似文献
5.
A. C. Balachandra Swamy 《Astrophysics and Space Science》1992,191(2):203-211
The thermal imbalance in theE-region heights is inescapable and an undisputed fact. The equatorial electrojet parameters are being evaluated for an Indian Equatorial station of Thumba, making use of the observed electron density, electron temperature, and current density profiles for two rocket flights on 3 March, 1973 and 7 April, 1972 around local noon, corresponding to low and medium solar active conditions. The computed Joule heating due to Equatorial Electrojet Current (EEC) does not account for the observed difference between the electron and neutral gas temperatures. The discrepancy of about 6 km in the peaks of the observed and computed current density profiles may be attributed to the presence of the Electromagnetic Drifts (EMD). In order to see whether or not EMD plays an important role, the photoionization balance between production and loss rates have been computed by making use of the latest available solar flux and cross sections and chemical reaction rate constants for the appropriate solar epoch conditions including the transport term due to EMD. There is an excellent agreement between the observed and computed electron density profiles indicating its relevance. 相似文献
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The influence of turbulence on the frequencies of free acoustic modes in convection zones is considered. The frequencies are modified via the speed of sound by the turbulence-induced alterations of the effective pressure: (i) by the correlated fluctuations of temperature and density and (ii) the pressure part of the Reynolds stress. The two effects shift the frequency of low l p-modes in opposite directions. In addition, the correlation of the density fluctuations with the random velocity — the eddy-mass flow — is also relevant. It is, in a steady state, balanced by a vertical mean velocity. The balance results in a rather small net effect completely disappearing for highly nonradial oscillations. Both effects of the density fluctuations produce a redshift of the low l p-mode frequencies. The Reynolds stress, however, makes a blueshift of the frequencies relative to that computed for a laminar gas. This effect dominates for subsonic turbulences. The applied second-order correlation-approximation, however, only holds for the lowest frequencies, where the KORONAS (solar minimum) data are indicating a blueshift. Of particular importance for the present concept is the expected cycle-variations of the lineshifts, i.e. the consideration of the magnetic modification of the various contributions. Observations may show whether the suggested modifications of the solar oscillation theory are correct. 相似文献
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The density dependence of solar EUV line intensity ratios from Mg VIII, Si VII, S IX and Si IX ions have been used to determine electron densities in the quiet Sun and coronal holes. The line intensity values have been computed using a model atmosphere of Kopp and Orrall (1976) in order to emphasize the utility of the lines studied which could be compared with observational data that future missions might provide. 相似文献
8.
R. Schwartz 《Astrophysics and Space Science》1971,14(2):286-300
41 galactic clusters containing stars with spectral types from O5 to B9 have been observed at frequencies of 1.4 GHz and 2.7 GHz. Only clusters with spectral types earlier than B1 show thermal radio emission. Emission measure, mean electron density, and mass ofHii gas have been computed from the observed data, and a comparison between the radio flux and H- and H-flux densities has been made. The ratio of hydrogen mass and total stellar mass of the clusters and the gas to dust ratio are given. 相似文献
9.
Theoretical line ratios for the A1viii ion have been investigated using an atomic model including the first fifteen energy levels, and taking account of various physical processes. The line emissivities as a function of electron density have been computed. Density-dependent theoretical line ratios are presented and their diagnostic applications in the solar atmosphere are discussed with the help of theoretical line intensities computed using an atmospheric model for the quiet Sun. 相似文献
10.
Fluxes have been computed for Fex (6374 Å) and Fe xiv (5303 Å) lines as a function of solar radii and at various coronal tempratures. The electron density derived from the white light corona during the total solar eclipse of 1980 were used in the computations. Fluxes in adjacent continua have also been computed. The computed ratios of line flux to the square of continuum flux at a coronal temperature of 1.6 × 106 K show a good fit with the observed values for Fex line. Further, radiative excitation seems to dominate over collisional excitation beyond 1.3 solar radius. 相似文献
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The transfer of polarized radiation in inhomogeneous circumstellar shells with a spheroidal spatial distribution of porous dust particles is computed. The grains are modeled by an MRN mixture of silicate and graphite particles. The optical properties of porous particles (considered separately in the Appendix) are computed by using effective medium theory and Mie theory. The following observational characteristics have been computed for WW Vul, a typical Herbig Ae star with Algol-like minima: the spectral energy distribution from the ultraviolet to the far infrared, the color-magnitude diagrams, the wavelength dependence of linear polarization, and the shell brightness distribution. The effect of grain porosity on the results is considered. It has been found that only moderate particle porosity (the volume fraction of matter is f ～0.5) can explain available observational data in terms of the approach used. Since radiation pressure must rapidly sweep submicron-sized grains out of the vicinity of Herbig Ae/Be stars, we briefly discuss how particle porosity can affect this process. 相似文献
12.
A propagation of diverging cylindrical shock in a self-gravitating gas, having an initial density and azimuthal magnetic field distributions variable, has been studied for the two cases (i) when the shock is weak and (ii) when it is strong. Analytical relations for shock velocity and shock strength have been obtained. Lastly, the expressions for the pressure, the density and the particle velocity immediately behind the shock have been also obtained for both cases. 相似文献
13.
A. Blanco A. Borghesi E. Bussoletti S. Nicolazzo A. M. Zambetta 《Astrophysics and Space Science》1976,41(2):447-474
Planck mean absorption cross-sections have been computed for spherical grains composed of graphite, iron, ice, olivine, amorphous quartz and a lunar silicate. Experimentally determined infrared optical constants have been used for all these materials. Ice mantle particles and planetesimal particles (iron core and olivine mantle) have also been considered with values of outer and inner radii covering a wide range of astrophysical conditions.The results given both graphically and in a tabular form are discussed and compared with those of other authors. The relationships of mantle and core properties are also critically discussed. 相似文献
14.
Line intensity ratios of NeVI lines with respect to a resonance line of MgVI have been considered for electron density and temperature determinations within the chromosphere-corona transition region. The electron pressure within the transition region has been assumed to be constant. In addition, these ratios would enable us to estimate the relative element abundances of neon to magnesium. An attempt has been made to explain the extreme ultraviolet intensities of NeVI and MgVI lines as observed by ATM ultraviolet spectrometer. The observed intensities correspond to the average quiet-Sun conditions near solar minimum. Theoretical intensities for NeVI and MgVI lines have been computed using a model solar atmosphere. Theoretical intensities obtained by using the values 3.98 × 10–5 and 3.16 × 10–5 for element abundance of Ne and Mg, respectively, seem to agree well with the expected intensities. The agreement between some of the expected and computed intensities suggests the need for future observations at higher spectral resolutions to resolve difficulties arising out of blending due to two or more lines. 相似文献
15.
One hundred and fifty-three diatomic molecules,molecular ions,and radicals of astrophysical interest
A critical analysis of the 583 available references in literature has been made to select 153 diatomic molecules, molecular ions, and radicals of astrophysical significance. The results have been arranged in a text-cum-tabular form. The compilation contains various information for each molecule, such as the dissociation energy, spectral region, transition levels, astrophysical objects where the respective molecules have been detected (say, comet, meteorite, Sun, planet, star, interstellar matter, Galaxy, etc.); computed theoretical parameters (i.e., FCFs, transition probabilities, r-centroids, PE curves), and available laboratory data with respective references.In many problems involving the estimation of the physical condition (viz., temperature, pressure, density, and abundance) of the emitter, in various cosmic sources, it is desirous to have a knowledge of the theoretical parameters as well as the experimental details for the molecular spectra of interest.A few important areas of active research in laboratory astrophysics have also been identified in this article: laboratory astrophysics, molecular cloud chemistry, isotopic abundance, planetary and cometary atmospheres through satellites.Besides, some interesting plots of the dissociation energy vs molecular weight, dissociation energy vs total atomic number, dissociation energy vs atomic number differences, ionization potential vs total atomic number, ionization potential vs atomic number differences, and ionization potential vs molecular weight for respective molecules have also been enumerated. Thirty-one new diatomic molecules/molecular ions/radicals of astrophysical significance have also been listed.Astrophysics and Space Science Review Paper. 相似文献
16.
Using the GADGET-2 code modified by us, we have computed hydrodynamic models of a protoplanetary disk perturbed by a low-mass companion. We have considered the cases of circular and eccentric orbits coplanar with the disk and inclined relative to its midplane. During our simulations we computed the column density of test particles on the line of sight between the central star and observer. On this basis we computed the column density of circumstellar dust by assuming the dust and gas to be well mixed with a mass ratio of 1: 100. To study the influence of the disk orientation relative to the observer on the interstellar extinction, we performed our computations for four inclinations of the line of sight to the disk plane and eight azimuthal directions. The column densities in the circumstellar disk of the central star and the circumbinary disk were computed separately. Our computations have shown that periodic column density oscillations can arise in both inner and circumbinary disks. The amplitude and shape of these oscillations depend on the system’s parameters (the orbital eccentricity and inclination, the component mass ratio) and its orientation in space. The results of our simulations can be used to explain the cyclic brightness variations of young UX Ori stars. 相似文献
17.
The energy and angular distributions of electrons have been studied by combining small angle scatterings using analytical treatment with large angle collisions using Monte Caroo calculations as a function of column density for initially power-law electron distributions and incidence angles of 0, 30, and 60°. Using these distributions the X-ray and EUV line flux as a function of column density has been computed. The flux increases with increase in column density. At the initial column densities the contribution of non-thermal electrons for the production of line flux is negligible. However, it becomes significant at intermediate column densities at which the electron energy and angular distributions have non-Maxwellian nature. X-ray and EUV flux have also been calculated as a function of electron spectral index at a fixed column density. It falls steeply with increase in spectral index. The calculated flux is compared with the observations. 相似文献
18.
Connecting atmospheric science and atmospheric models for aerocapture at Titan and the outer planets
Many atmospheric measurement systems, such as the sounding instruments on Voyager, gather atmospheric information in the form of temperature versus pressure level. In these terms, there is considerable consistency among the mean atmospheric profiles of the outer planets Jupiter through Neptune, including Titan. On a given planet or on Titan, the range of variability of temperature versus pressure level due to seasonal, latitudinal, and diurnal variations is also not large. However, many engineering needs for atmospheric models relate not to temperature versus pressure level but atmospheric density versus geometric altitude. This need is especially true for design and analysis of aerocapture systems. Drag force available for aerocapture is directly proportional to atmospheric density. Available aerocapture “corridor width” (allowable range of atmospheric entry angle) also depends on height rate of change of atmospheric density, as characterized by density scale height. Characteristics of hydrostatics and the gas law equation mean that relatively small systematic differences in temperature versus pressure profiles can integrate at high altitudes to very large differences in density versus altitude profiles. Thus, a given periapsis density required to accomplish successful aerocapture can occur at substantially different altitudes (∼150-300 km) on the various outer planets, and significantly different density scale heights (∼20-50 km) can occur at these periapsis altitudes. This paper will illustrate these effects and discuss implications for improvements in atmospheric measurements to yield significant impact on design of aerocapture systems for future missions to Titan and the outer planets. Relatively small-scale atmospheric perturbations, such as gravity waves, tides, and other atmospheric variations can also have significant effect on design details for aerocapture guidance and control systems. This paper will discuss benefits that would result from improved understanding of Titan and outer planetary atmospheric perturbation characteristics. Details of recent engineering-level atmospheric models for Titan and Neptune will be presented, and effects of present and future levels of atmospheric uncertainty and variability characteristics will be examined. 相似文献
19.
The dynamical evolution of six open star cluster models is analyzed using the correlation and spectral analysis of phase-space density fluctuations. The two-time and mutual correlation functions are computed for the fluctuations of the phase-space density of cluster models. The data for two-time and two-particle correlations are used to determine the correlation time for phase-space density fluctuations ((0.1–1) τ v.r., where τ v.r. is the violent relaxation time of the model) and the average phase velocities of the propagation of such fluctuations in cluster models. These velocities are 2–20 times smaller than the root mean square velocities of the stars in the cluster core. The power spectra and dispersion curves of phase-space density fluctuations are computed using the Fourier transform of mutual correlation functions. The results confirm the presence of known unstable phase-space density fluctuations due to homologous fluctuations of the cluster cores. The models are found to exhibit a number of new unstable phase-space density fluctuations (up to 32–41 pairs of fluctuations with different complex conjugate frequencies in each model; the e-folding time of the amplitude growth of such fluctuations is (0.4–10) τ v.r. and their phases are distributed rather uniformly). Astrophysical applications of the obtained results (irregular structure of open star clusters, formation and decay of quasi-stationary states in such clusters) are discussed. 相似文献
20.
Fine time variation of hard X-rays has been explained in terms of a spread in the angle of incidence of the source electrons in non-thermal thick-target model for bremsstrahlung generation. The electron energy and angular distributions have been calculated by combining small angle scatterings using analytical treatment with a large angle collision using Monte Carlo calculations as a function of column density. The incidence angles of electrons are taken as 0, 30, and 60°. Using the Bethe-Heitler cross section and the above calculated electron distributions, the bremsstrahlung flux for different photon energies as a function of column density has been studied. The computed X-ray pulse as a function of column density has been converted into time profile. It corresponds well with the observed fine time structure. The calculated spectra of X-rays at the peak and valley are also consistent with the observations. The variation of photon flux with time has also been computed for photon energies 20, 50, and 100 keV for 90 and 180° observation angles together with the changes in spectral shapes of photon energy spectrum at different times for 90 and 180° observation angles. 相似文献