Showing papers in "The Astrophysical Journal in 1959"

Estimates of the Total Energy in Particles and Magnetic Field in the Non-Thermal Radio Sources.

Abstract: A summary of the estimates (made in 1958) of the total energy in particles and magnetic field in the non-thermal galactic and extragalactic sources are given. These estimates are obtained from calculations by the theory- of synchrotron radiation. (C.J.G.)

A Revised Table of Abundances of the Elements.

Abstract: The semiempirical abundance table of Suess and Urey has been very helpful to nuclear physicists in determining the relative importance of various mechanisms of nucleogenesis in contributing to the natural abundances of the elements. The table was based primarily on abundance determinations in chondritic meteorites, together with the hypothesis that the abundances of odd mass-number nuclides should lie on a smooth curve. It has recently become apparent that certain elements are over- or underabundant in the chondritic meteorites without apparent chemical reason. In order to throw additional light oil such discrepancies and on certain less well-understood mechanisms of nucleogenesis, the abundance-curve has been re-examined, using some additional nucleogenesis-based criteria for the abundances of evcn mass-number nuclides, and a new table of abundances has been constructed. It was found necessary to change the Suess-Urey table substantially in the rare-enrth region and in the lead region and to make isolated changes in the abundances of certain additional elements. Some conclusions have been drawn regarding the process of neutron capture on a fast time scale and the methods of production of bypassed heavy nuclei. (auth)

Neutron Star Models.

Abstract: An equation of state for a neutron gas, derived from the work of T. H. R. Skyrme, is given. Relativistic forms of the terms in the equation were not used. At densities of >10/sup 15/ g/cc where relativistic terms would be important, this equation is not expected to be valid. The general relativistic equations of hydrostatic equilibrium are given for which there are no solutions for proper masses in excess of three stars. It does not appear likely that much more than one star mass will condense to form a neutron star in a supennova explosion, and stable solutions should exist for such a case. (B.O.G.)

The Opacity at High Temperatures due to Compton Scattering.

Abstract: The contribution to the radiative opacity of matter arising from Compton scattering is obtained for the entire region in which degeneracy in the electron distribution may be neglected. This corresponds to temperatures up to about 125 kev (1 kev = 11605800 deg K) and densities up to roughly 10/sup -4/ g cm/sup -3/ at the highest temPeratures considered. It is found that, at temperatures for which the Klein-Nishina cross section should be used, parts of the scattering into and out of a beam of radiation do not cancel, as previously assumed. The result of this is to lower the opacity by about 13 per cent at kT = 20 kev and 37 per cent at kT = 125 kev. Although absorption resulting in pair-creation may be neglected at these temperatures, it is found that pair production is responsible in another way for a sharp rise in the opacity by increasing the density ( N) of electrons and positrons significantly at the highest temperatures considered. In fact, at kT = 125 kev, the value of N corresponding to thermal equilibrium is large and almost independent of the matter density (p), where p does not include the mass of the electrons andmore » positrons resulting from pair-creation. Hence, it is concluded that for kT > 125 kev, the average mean free path A/sub c/ = (pKc)/ sup -1/ is small and independent of p. On the other hand, for kT < 30 kev, one has the familiar situation that the Compton opacity (K) is small and independent of p. (auth)« less

The rate of star formation in the galaxy

Abstract: A method is described for obtaining time sequences of stellar configurations automatically by means of highspoed digital computers. The time- dependent differential equations of stellar structure are replaced by secondorder difference equations. These non-linear difference equations, together with the boundary conditions, are solved by an iterative method which is a generalization of the Newton-Raphson method for obtaining roots of functions. With the UNIVAC computer of the Livermore slte of the Lawrence Radiation Laboratory, the method has been used in connection with various previously published studies of stellar evolution. (auth)

The rotation and mass of ngc 1808.

Abstract: Dusty Sb galaxy NGC 1808 velocity field, rotation, mass and mass/light ratio, noting circular motion departures and interstellar gas