Simulation of large-scale gas structures formed in the interaction between galaxies. I. Method and preliminary results

Computer programs developed to study large-scale, transient gas structures in galaxies are described and test results are given. Gas-dynamic quantities are determined on the basis of a three-dimensional algorithm using so-called "smoothed particle hydrodynamics" (SPH). Preliminary calculations were made to simulate the formation of a gas ring around a spheroidal galaxy when it absorbs a low-mass, gas-rich companion, as well due to gas accretion during the flyby of a spiral galaxy of comparable mass. The evolution of tidal gas tails of disk galaxies is investigated.Translated from Astrofizika, Vol. 39, No. 2, pp. 265–284, April–June, 1996.     

A filament eruption and accompanying coronal field changes on November 5, 1992

An H filament eruption on November 5, 1992 was fully observed in H with the Hida Flare Monitoring Telescope, while Yohkoh's Soft X-ray Telescope observed the pre- and post-eruption evolution of the coronal magnetic fields. From the H data, including the red and blue wings, we have reconstructed the rise of the filament, including trajectory, velocity, and acceleration. In combination with the Yohkoh data this reconstruction suggests that the filament had several interactions with other coronal magnetic fields during the eruption. The Yohkoh data also shows pre-eruption changes in the coronal fields and several post-eruption bright coronal structures. The pre-eruption changes are interpreted as a partial opening of the corona, indicating that it is not necessary to have a complete opening of the corona in order for a filament to erupt and we discuss the several possible contributions from emerging flux. The post-event bright coronal structures are compared with theory and with a cleaner filament eruption event on July 31, 1992. These comparisons suggest that, although there are many similarities, it is hard to completely reconcile the observations with the existing theory.     

Imaging coronal emission lines under high sky-background conditions

We have obtained images in solar coronal emission lines under high sky-background conditions by making precise differential measurements between the coronal emission line and the near-by continuum, which is primarily due to scattered light from the solar disk. Chopping between the two wavelengths was performed at 100 kHz to avoid artifacts from fast-flying dust particles and other aerosols, and also from seeing effects. The differential signal was detected with a novel CCD camera that demodulates signals up to 100 kHz. These preliminary observations show coronal emission at the 0.2% level of the scattered-light background and pave the way to efficient and precise imaging of coronal emission features under less than ideal coronal-sky conditions.Operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under cooperative agreement with the National Science Foundation.     

Radiation-hydrodynamic waves and global solar oscillations

We investigate nonadiabatic hydrodynamic waves in a nongrey, radiating, thermally conducting, homogeneous atmosphere in LTE with a finite mean free path of photons. Avoiding the Eddington approximation the remaining simplifications in the basic equations are discussed, the generalized dispersion relation is analysed, and some wave properties in a grey model are studied. The properties of waves in a stratified atmosphere are analysed as well. In connection with the predicted properties of the nonadiabatic waves we discuss observations ofp-modes by measuring brightness fluctuations.     

Regional development in the United States during the 1980s: population redistribution and economic restructuring

The reduction of the rate of growth of the Brazilian population from 3% in the 1960s to 2% by 1993 resulted from a significant reduction of fertility. According to the 1986 national maternal-child health and family planning survey (PNSMIPF) results, 43.3% of women were using some type of contraception: 65.6% of married or cohabiting women. Women relied most on sterilization (17.2%), followed by oral contraceptives (OCs) (17%), the rhythm method (2.8%), the condom (1.1%), and others (5.2%). Only in the south was OC use more prevalent (28.5%) than sterilization (12.2%). The proportion of sterilization reached 27.8% in the north/center-east urban regions. In urban areas sterilization averaged 18.7% vs. 12.7% in rural areas. 26.9% of currently married women in the age range of 15-44 years had been sterilized. A 1990 international estimation indicated that the proportion of sterilization amounted to 36.9% in China, 30.95 in India, 29.7% in Brazil, 47.6% in South Korea, 30.4% in Thailand, and 36.5% in the Dominican Republic. The 1986 PNSMIPF survey also indicated that sterilized women were better informed than other women about contraception. 75% of the former had used OCs, 5% had used the diaphragm, 3% the IUD, 30% the condom, and 35% coitus interruptus at one time or other. The sterilized women had an average of 1.7 more children than those who were using other methods of contraception. 48.6% of women were sterilized before the age of 30, when they had had an average of 3.6 children. 66.6% of the sterilized women who had given birth before the age of 20 had 4 or more live births as compared to 5.9% of sterilized women aged 30 with the same number of children. 47% of women without any schooling were using some kind of contraception vs. 77% of those who had completed secondary school. A multivariate analysis also showed that the age of the mother, the number of live births, the educational status of the mother, and family income were positively correlated with sterilization.     

Morphology and variability of helium line profiles in the P Cygni spectrum

The morphology and variability of 13 helium lines in the P Cygni optical spectrum have been studied in detail over a period of three years. It is found that most lines in the sample have often shown profiles with a complicated structure: discrete components are superposed on a broader underlying P Cyg profile. Multiple sets of components were frequently observed. The radial velocity of the discrete components varies with time. In this article the velocity evolution of two sets of components is studied in detail and the corresponding velocity laws are derived. It is found that the velocity variations in the helium and hydrogen discrete components are correlated. The recurrence timescale for the appearance of new helium components is estimated.An attempt is made for a qualitative interpretation of the obtained results.     

The inverse planetary problem: a numerical treatment

The so-called inverse planetary problem can be stated as follows: given the distances from the centre, masses, and radii of (say) three planets of a planetary system, find the optimum polytropic index, mass, and radius of their star, and also other quantities of interest, which depend either explicitly or implicitly on the foregoing ones (e.g., central and mean density, central and mean pressure, central and mean temperature, etc.). It is hereafter tacitly assumed that the system is opaque with respect to observations concerning periods of planetary otbits; hence, we cannot have any relevant estimates due to the well-known period laws. In the present paper, the inverse planetary problem is treated numerically on the basis of the so-called global polytropic model, developed recently by the first author.     

Multiple flows and the fine structure of the transition region around sunspots

The fine structure in the flow field in the transition region above and surrounding a sunspot is determined fromCIV 1548 line profiles, observed with the High Resolution Telescope and Spectrograph (HRTS) during the Spacelab 2 mission. The observed line profiles show one, two, or three distinct velocity components within the resolution element of 1 × 1. Supersonic flows occur in small regions where the line profile has two or three components. The line component that shows supersonic speed often is weaker than the subsonic line component, which may explain why some observers have been unable to detect the supersonic flow component. The broadening of individual line components shows non-thermal velocities close to 20 km s^–1. This suggests that turbulence is less important than usually considered.The presence of multiple flows, which also occurs in quiet solar regions, suggests that the transition region above sunspots has a sub-arc-second fine structure, perhaps consisting of thin fibrils. The Evershed flow in the transition region appears to have a correspondingly complex character, possibly consisting of sub- and supersonic siphon flows along the individual fibrils. Time changes in the flow field over 5 min may correspond to characteristic times of individual fine structures. Possible explanations of the net downward directed mass flux are presented.     

A quasi-one-dimensional velocity regime of super-thermal electron stream propagation through the solar corona

The propagation of an inhomogeneous-stream of fast electrons through the corona-the type III radio burst source - is considered. It is shown, that the angular spectrum width of plasma waves excited by the stream is defined both by Landau damping by particles of the diffuse component and by damping (in the region of large phase velocities) by particles of the stream itself having large pitch angles. The regime of quasi-one-dimensional diffusion in the velocity space is realized only in the presence of a sufficiently dense diffuse component of super-thermal particles and only for a sufficiently large inhomogeneity scale of the stream. A large scale of the stream space profile is formed, evidently, close to the region of injection of super-thermal particles. It is the result of stripping of part of the electrons from the stream front to its slower part due to essential non-one-dimensionality of the particle diffusion in velocity space.Results obtained may explain, in particular, the evolution of a stream particle angular spectrum in the generation region of type III radio bursts observed by spacecrafts (Lin et al., 1981). For the relatively low energetic part of the stream, the oblique plasma wave stabilization by a diffuse component results in a quasi-one-dimensional regime of diffusion. The latter conserves the beam-like structure of this part of the stream.     

On the mass distribution law of systems of protocluster fragments

Starting from the hypothesis of coalescence through inelastic collisions of small fastmoving interstellar gas clouds, an attempt has been made to study the evolutionary mass distribution of a system of fragments simulating a protocluster. The assumption of a mass spectrum with a continuous injection of newly formed entities into the primeval system, and the condition of gravitational reduction of the impact cross-section, have been considered. Comparisons of numerical experiments with the mass spectrum in some well-known young galactic clusters, confirm the mass distribution power-law already obtained by other authors. The empirical Schmidt's law concerning the rate of star formation is also confirmed. The hypothesis of the universal validity of the luminosity function, should not be a priori rejected.