Theoretical properties of radio-galaxies

We present optical photometric observations of the cataclysmic variables AO Psc and V 1223 Sgr, both of which are believed to contain slowly-rotating white-dwarf pulsars. These objectes belong to the new class of intermediate polars in which the magnetized-white-dwarf rotation period lies in between synchrous and extremely fast rotation periods. The observations reported here were carried out from the Kavalur Observatory using a 1 m reflector. High-time resolution light curves depicting a rich variety of flicker phenomena are presented. Results of a periodic analysis to search for coherent periodic modulations in the light curves are also presented. We have also derived the optical pulse profile of AO Psc and point out its similarities to the X-ray pulse profile.     

X-rays from radio-galaxies: BeppoSAX observations

We briefly review BeppoSAX observations of X-ray bright radio-galaxies. Their X-ray spectra are quite varied, and perhaps surprisingly, any similarity between radio-loud AGN and Seyfert galaxies is the exception rather than the rule. When detected, re-processing features (iron line and reflection) are generally weak, suggesting two possible scenarios: either: (1) non-thermal (jet?) radiation dilutes the X-ray emission from the disk in radio-loud objects, or (2) the solid angle subtended by the X-ray re-processing material is smaller in radio-loud than in radio-quiet AGN due to different characteristics of the accretion disk itself.     

Rediscussion of balmer decrement of broad-line radio-galaxies

On the basis of the erenkov line emission theory in the optically thick case, a new interpretation of intensity ratios H/H and H/H in broad-line radio-galaxies (BLRGs) is reported. Calculation shows that if the theoretical ratio H/H is just taken to be the mean observed value 0.21, equivalently, the parameterX(H)=3.0, then the expected ratio H/H=6.70 is almost the same as the observations. By comparing these values with the previous investigations of QSOs (X(H)=20.9), we conclude that the number density of neutral hydrogen gas in BLRGs is almost one order-of-magnitude smaller than that in the QSOs.Preliminary verification of the erenkov line emission has been obtained by Xuet al. (1981) in the laboratory.     

Examples of clustering around high redshift radio-galaxies

Published in Astrofizika, Vol. 38, No. 4, pp. 677–680, October–December, 1995.     

Theoretical models for Mars and their seismic properties

Theoretical seismic properties of the planet Mars are investigated on the basis of the various models which have been proposed for the internal composition of the planet. The latest interpretation of gravity field data (Reasenberg, 1977), assuming a lower value of the moment of inertia, would require a less dense mantle and a larger core than previous models. If Mars is chondritic in composition, the most reasonable models are an incompletely differentiated H-chondrite or a mixture of H-chondrites and carbonaceous chondrites. Seismic profiles, travel times, and free oscillation periods are computed for various models, with the aim of establishing which seismic data is crucial for deciding among the alternatives. A detailed discussion is given of the seismic properties which could—in principle—help answer the following two questions: Is Mars' core liquid or solid? Does Mars have a partially molten asthenosphere in its upper mantle?     

Theoretical interpretation of photometric properties of the Martian surface and atmosphere

Earth-based UBV photometry, high-quality photographs from the Lowell Observatory collection, and Mariner 9 data have been combined with a new radiative transfer theory to derive physical parameters for the Martian surface and atmosphere, both before and during the 1971 dust storm. We find that the dust particles of the storm had a single-scattering albedo of 0.84 ± 0.02 and an asymmetry factor of 0.35 ± 0.10 in green (V) light. The geometric albedo of Mars was 0.15 and the phase integral 1.83, which yield 0.27 for the Bond albedo. The mean optical thickness of the “clear” atmosphere averaged over the whole planet was 0.15 ± 0.05 and was not detectably dependent on wavelength. Geometric albedos for the surface are 0.25 (light areas) and 0.17 (dark areas) in V, 0.095 in B (both areas), and 0.060 in U (both areas). The soil particles are moderately backward scattering with an asymmetry factor of ?0.20, indicating them to be rather opaque. The mean surface roughness, on a scale larger than that of individual dust particles and therefore large compared with the wavelength, is 0.57. This represents the depth/radius ratio of an average hole and it is only one-half as large as values typical for the Moon and asteroids.     

Theoretical calculation of Martian airmass

Analysis of spectroscopic observations of Mars requires values of the effective Martian airmass to obtain true abundances. Semi-arbitrary assumptions for the airmass correction have been used in most of the past publications on the subject. We have computed detailed values corresponding to specified slits superimposed on the disk of the planet, giving useful output in the form of curves presenting the average airmass for different regions of the planet and various conditions of planet diameter, seeing and phase angle.     

关于磁流体力学流动的一些理论研究

本文介绍关于磁流体力学（ＭＨＤ）流动理论研究的一些结果．在所研究的流动中，允许流速垂直于磁场，允许各物理量随时间变化．在各有关的守恒定律和感应方程中引进代换，不经过求解，用严格的解析方法获得了有关解的某些性质．文中给出一个简单的例子．在其中计算二维沿磁力线的稳恒态ＭＨＤ流动．     

Theoretical models of planetary nebulae

Theoretical models are calculated for 15 planetary nebulae of medium-to-high excitation, following procedures previously described. Initial stellar energy distributions are adopted from Cassinelli (1971), but are subsequently modified to obtain the best representation of optical spectra for the selected objects. Other adjustable parameters include the stellar radius,R ^(*), the nebular density,N _H, the truncation radius,r _c, for the nebular shell, and the chemical composition. Excitationsensitive ratios are usually well-represented as are the actual observed intensities of spectral lines. Forbidden lines arising from 3p ³ configurations, e.g., those of [SII], [ArIV], and [ClIII] offer difficulties. For this sample of nebulae, the mean abundances seem to agree well with those found in an earlier study where the models were used as interpolation devices (Aller, 1978). Our objective is not to use the models to derive abundances explicitly, but rather to use them to find ionization correction factors. Some cautions and limitations of this procedure are described.     

Theoretical models of planetary nebulae

Theoretical models are attempted for eight moderate excitation planetary nebulae which have been intensively observed with the image-tube scanner at Lick and in other investigations. The models are uniform density structures, often truncated, with central star energy distributions and chemical compositions so adjusted as to give an optimum fit with the observations. Although a satisfactory representation can be obtained for most of the stronger, usually observed lines, those arising from the 3p ³ configuration, specifically the nebular transitions of [Sii], [Cliii], and [Ariv], often give difficulties. A comparison with results of model predictions with those from simple, traditional procedures generally shows a good agreement, except in those instances where different judgments are made in interpreting emissions of ions of 3p ⁿ configurations.     

Theoretical profile of Saturn's rings

Steady-state solutions for the optical thickness of Saturn's rings are studied in terms of Hämeen-Anttila's (1983) theory of bimodal gravitating systems. The elastic properties of particles determine the behaviour of the rarefied mode (gaps), while the dense mode (ringlets) depends on the size and the internal density of the particles. In the outer parts of the rings the dense mode is unstable against the growth of gravitational perturbations. Inside the Roche distance this produces only very narrow ring-shaped configurations with helical orbits around them, and the system is not destroyed. The outer boundary of the rings corresponds to the distance beyond which the gravitational instability transforms the dense mode into strictly local condensations (moons). The inner boundary of the ring system is caused by the absence of dense mode near Saturn. The rarefied mode is stable in a larger region.     

Theoretical spectra of cataclysmic variables

We present two methods of modelling accretion disks in dwarf novae. The first one determines self-consistently the structure of a disk together with the radiation field. The computed theoretical spectra agree well with the observations of the dwarf nova WX Hyi in quiescence as well as in superoutburst. The second method is a modification of Tylenda's (1981) approach. We have used it to calculate models of disks around main-sequence accretors. The most interesting result is that no unique solution exists for a moderate mass flux around 10^–6 Myr^–1. Such disks are thus probably unstable.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F.R.G., 16–19 June, 1986.     

Theoretical models of planetary nebulae

Sets of theoretical models of spherically symmetrical gaseous nebulae are calculated for a fixed chemical composition and with central star, energy distributions given by Cassinelli (1971) and by Kunasz, Mihalas and Hummer (1975). A central region of constant densityN _H=100 cm^–3 is surrounded by a broken shell consisting of zones of different density and optical thickness. It is found that for a fixed chemical composition and central star flux, a considerable range can be found in the emitted fluxes of certain lines such as 4686 which are often used to fix the level of excitation of a nebula. Although it is possible to produce models yielding a variety of nebular line ratios in this way, these truncated inhomogeneous shell models have not reproduced the integrated spectra of nebulae that simultaneously show extreme features of high and low excitation with great strength-e.g. [Nii], [Oii] and 4686 Heii.     

Theoretical models of planetary nebulae

Introduction of the O⁺⁺+H⁰O⁺+H⁺ charge exchange rate suggested by Butler, Bender and Dalgarno leads to theoretical nebular models that differ from those previously computed in several important respects. Different elemental abundances, bluer central star energy distributions, and truncated (material limited) models are required. If the argon abundance is fixed from the 7135 [Ariii] line intensity, 4740 [Ariv] is invariably predicted to be much too strong. Better atomic parameters, together with improved charge exchange rates for other ions, and more accurate dielectronic recombination rates may alleviate the situation.     

Theoretical chromospheric flare spectra

Solar Physics - Nous publions ici les résultats des observations coronographiques que nous avons effectuées à l'Observatoire du Pic-du-Midi à l'occasion des...     

Theoretical twin meteor showers

Attention is drawn to, and theoretical radiants calculated for, 27 hypothetical twin showers to Cook's (1973, in Evolutionary and Physical Properties of Meteoroids, NASA SP-319, U.S. Govt. Printing Office, Washington, D.C.) working list of meteor streams. Of these twin showers, 7 are previously known, 1 is a night-time twin to the ? Geminids, 9 are found to be contained among Sekanina's (1976, Icarus27, 265–321) radar streams, and the remaining 10 are undetected daytime showers. Minimum radii are computed for all of Cook's streams and are used to assess the possibility of detecting the twin showers.     

Theoretical interpretation of cosmic magnetic fields

The paper discusses the possibilty of interpreting the magnetic fields of astronomical bodies in the framework of a unified field theory.Using one of the solutions of the generalized field theory, a direct relation between the polar magnetic field, the angular velocity and the gravitational potential of the body considered, is obtained. The geometric model used for applications has spherical symmetry and is of the type (FIGI).The predictions of the theoretical formula, obtained from the model, are compared with available observational data, and with the empirical formula of Blackett. The theoretical formula gives a possible interpretation of a seed magnetic field which will develop and produce the large-scale magnetic field observed for celestial objects. The formula shows that the field is generated as a result of rotation of a massive object.     

Theoretical model of flares and prominences

A theoretical model of flare which explains observed quantities in H, EUV, soft X-ray and flare-associated solar wind is presented. It is assumed that large mass observed in the soft X-ray flare and the solar wind comes from the chromosphere by the process like evaporation while flare is in progress. From mass and pressure balance in the chromosphere and the corona, the high temperature in the soft X-ray flare is shown to be attained by the larger mass loss to the solar wind compared with the mass remained in the corona, in accord with observations. The total energy of 10³² erg, the electron density of 10^13.5 cm^–3 in H flare, the temperature of the X-ray flare of 10^7.3K and the time to attain maximum H brightness (600 s) are derived consistent with observations. It is shown that the top height of the H flare is located about 1000 km lower than that of the active chromosphere because of evaporation. So-called limb flares are assigned to either post-flare loops, surges or rising prominences.The observed small thickness of the H flare is interpreted by free streaming and/or heat conduction. Applications are suggested to explain the maximum temperature of a coronal condensation and the formation of quiescent prominences.     

Theoretical modelling of SiO maser lineshapes

Various factors affecting the lineshapes of SiO masers have been considered: saturation, competitive gain, velocity redistribution and properties of the circumstellar envelope supporting the masers. The lineshape of a single maser spot is likely to be dominated by conditions of complete velocity redistribution (CVR) for low to moderate amplification, changing to NVR (no velocity redistribution) only for strongly saturating masers. Both CVR and NVR regimes can produce peculiar lineshapes. When many maser cells were considered, distributed at random in the stellar envelope, the individual lineshapes were combined to produce synthetic spectra. Maser action is predicted in higher rotational transitions than those observed to date, for example the J=7-6 transition of v=2.