Bianchi type-II perfect fluid solutions

It is shown that the recent new Bianchi type-II solutions of Hajj-Boutros (1986a, b) do not exist. We present a consistent method for perfect fluid solutions in this paper.     

Development of a real-time algorithm for detection of solar wind discontinuities

A study is presented of an algorithm, based on the statistical analysis of interplanetary magnetic field data, for the real-time detection of discontinuities in the solar wind. The analysis is based on the application of a sliding or searching algorithm together with a minimum variance treatment. A demonstration is given for a Pioneer data set from 29 August, 1966. This particular data set was chosen because it has been extensively studied (in terms of the fast forward MHD shock wave) by previous groups who utilized the three-dimensional Rankine-Hugoniot shock equations after identifying the shock on a subjective basis. Our procedure differs in that it is perfectly objective because of its searching technique. For this particular data set we identify the original shock with excellent agreement with the earlier studies of its normal vector, as well as an additional shock and tangential discontinuity, neither of which had been identified previously.     

Main sequence for rotating stars of intermediate mass

We have investigated the evolutionary behaviour of intermediate mass (2, 3, 4, 5, and 7M ) Population I stars, assuming two different rates of rotation at the threshold of stability.In the first part of the study, stars are assumed to start with a critical rotation (fast rotation model) and to progress to the point of rotational instability. The stars evolve by losing mass and become rotationally unstable before they reach the zero-age Main Sequence. It is argued that multiple star systems might be formed through the evolution of rapidly rotating stars. An expression for the rotational mass loss rate is derived as a function of the physical parameters of stars.In the second part of the study, stars are assumed to rotate at a rate below the critical value (slow rotation model). The evolution of slowly rotating stars is followed as far as zero-age Main Sequence on the theoretical Hertzsprung-Russell diagram and compared with that of normal stars. The evolutionary paths are found to be more or less similar to those of normal stars; but their positions on the Main Sequence are characterized by effective temperatures and luminosities lower than those of normal stars. The zero-age Main-Sequence times of these stars are longer than those of normal stars. The rotational rates obtained for the zero-age Main Sequence are in good agreement with observed values.     

A note on the total mass of comets in the solar system

The assumption that the very low albedo determined for Halley's comet is typical of all short period comets, taken together with the assumption that the average sizes of long and short period comets are approximately equal, leads to an increase in the total mass of comets in the solar system by almost two orders of magnitude. If gravitational ejection from the Uranus - Neptune zone during the later phases of planet formation is indeed responsible for the classical Oort cloud between 10⁴–10¹⁵ AU, then the mass of comets in this transplanetary region during cosmogonie times has to exceed the combined masses of Uranus and Neptune by over an order of magnitude. Furthermore, if the recent arguments for as many as 10¹⁴ comets in an inner Oort cloud between ~40– 10⁴AU are valid, then the total mass of comets in the solar system approaches 2% of a solar mass.     

Premature mortality in the Republic of Ireland

Regional variations in the incidence of premature deaths between 1971 and 1981 arc examined by mapping standardised mortality ratios for deaths under the age of 65. Premature mortality is also examined with regards to the number of years of normal life lost by those who die prematurely, using a specially defined unfulfilled life index. Unfulfilled life and premature deaths arc found to have a higher incidence in the major urban areas and a lower incidence in western counties, although there are some interesting differences in their spatial distributions. Differences with regard to sex. age at death and cause of death are also examined.     

An UV survey of the galactic plane

The present paper is the introduction to a systematic analysis of 123 6-degree fields near the galactic plane, recorded in the medium ultraviolet (2000 Å) by the ballon-borne experiment SCAP 2000 of the Laboratoire d'Astronomie Spatiale, Marseille, and Geneva Observatory. The available data are presented and the general properties of the images are briefly discussed.It is shown that the high selectivity of the UV passband regarding spectral type, together with the strong interstellar extinction at that wavelength, provide the necessary conditions for an efficient application of Wolf's method to study the distribution of interstellar matter in the solar neighbourhood. The results of a fast analysis of the available data are presented here.     

Analysis of a white-light flare spectrum

The continuum emission of an X₁ flare on 26 March, 1970 observed close to the solar limb (N 05 E 64) was analyzed by a photometric determination of the contrast I()/I ₀() in the wavelength range 3558–5920 Å. Two possible mechanisms for the emission were investigated, namely hydrogen Paschen and H^– continua. We show the unlikeness of the Paschen possibility and derive strong constraints on the temperature structure and energy deposition mechanism imposed by the H^– continuum process.We conclude that the emission must have originated in deep atmospheric layers. The relevance of this result with respect to flare energy release and transport processes is also discussed.     

The diameter of the sun at decameter wavelengths

Using observations obtained with the Clark Lake radioheliograph we determined the diameter of the Sun in the decameter wavelength range. Both equatorial and polar diameters increase with decreasing frequency, as D=Af . The eccentricity of the brightness distribution appears to remain constant in the frequency range (30–74 MHz) in good agreement with the optical results in a corresponding height range. The smaller size of the polar diameter is attributed to coronal holes covering the poles during the period of our observations, while streamers were observed at the equator most of the time.     

Hydrodynamical models of type II supernovae

A series of hydrodynamical models of type-II supernova outbursts (SNII) has been calculated. Approximate relations connecting the total outburst energy ε, the mass of envelope ejectedM, the presupernova radiusR, and the amount of ionizing quanta radiated by the supernovaeN _H with such values as the duration of the light curve plateau Δt, and absolute magnitude in the wavelength bandV and photospheric velocityU _PH observed near the middle of the plateau have been established. Advantage has been taken of the relations to obtain a preliminary evaluation for the characteristics of the average SN II: ε=7×10⁵⁰ erg,M=6M _⊙,R=500R _⊙,N _H=2×10⁵⁸. The SNIIs with plateau-like light curves seem to be accounted for by thermonuclear explosions of degenerate cores of red giant stars and result in a total disruption of the star without any stellar remnant. To the contrary, SNIIs with linear light curves have substantially different properties (in particular, they throw considerably less massive envelopes off). These SNII must signify the birth of collapsed objects—neutron stars (pulsars) or black holes.     

Variability of carbon monoxide in the mars atmosphere

In January of 1982 we measured a microwave spectrum of CO in the Martian atmosphere utilizing the rotational J = 1 → 2 transition of CO. We have analyzed data and reanalyzed the microwave spectra of R. K. Kakar, J. W. Waters, and W. J. Wilson, (Science196, 1090–1091, 1977, measured in 1975) and J. C. Good and F. P. Schloerb, (Icarus47, 166–172, 1981 measured in 1980) in order to constrain estimates of the temporal variability of CO abundance in the Martian atmosphere. Our values of CO column density from the data of Karar et al., Good and Schloerb, and our own are 1.7 ± 0.9 × 10²⁰, 3.0 ± 1.0 × 10²⁰, and 4.6 ± 2.0 × 10²⁰cm^?2, respectively. The most recent estimate of CO column density from the 1967 infrared spectra of J. Connes, P. Connes, and J.P. Maillard, (Atlas de Spectres Infarouges de Venus, Mars, Jupiter, et Saturne, Editions due Centre National de la Recherche Scientifique, Paris, 1969), is 2.0 ± 0.8 × 10²⁰ cm^?2 (L.D.G. Young and A.T. Young, Icarus30, 75–79, 1977). The large uncertainties given for the microwave measurements are due primarily to uncertainty in the difference between the continuum brightness temperature and atmospheric temperatures of Mars. We have accurately calculated the variation among the observations of the continuum (surface) brightness temperature of Mars, which is primaroly a function of the observed aspect of Mars. A more difficult problem to consider is variability of global atmospheric temperatures among the observations, particularly the effects of global dust storms and the ellipticity of the orbit of Mars. The large bars accompanying our estimates of CO column density from the three sets of microwave measurements are primarily caused by an assumed uncertainty of ±10°K in our atmospheric temperature model due to possible dust in the atmosphere. A qualitative consideration of seasonal variability of global atmospheric temperatures among the measurements suggests that there is not strong evidence for variability of the column abundance of CO on Mars, although variability of 0–100% over a time scale of several years is allowed by the data set. The implication for the variability of Mars O₂ is, crudely, a factor of two less. We found that the altitude distribution of CO in the atmosphere of Mars was not well constrained by any of the spectra, although our spectrum was marginally better fitted by an altitude increasing profile of CO mixing ratios.