Approximate analytic solutions to the isothermal Lane–Emden equation

We derive accurate analytic approximations to the solution of the isothermal Lane–Emden equation, a basic equation in Astrophysics that describes the Newtonian equilibrium structure of self-gravitating, isothermal fluid spheres. The solutions we obtain, using analytic arguments and rational approximations, have simple forms, and are accurate over a radial extent that is much larger than that covered by conventional series expansions around the origin. Our best approximation has a maximum error on density of 0.04 % at 10 core radii, and is still within 1 % from an accurate numerical solution at a radius three times larger.     

Field solution for a dipole in an anisotropic medium containing time-varying irregularities

Field solutions for a dipole in an anisotropic plasma medium are obtained in the presence of an infinitesimally small electric current source and time-varying irregularities through the use of inverse Fourier-transform technique. The derived solutions can be utilized for the evaluation of the field at an arbitrary distance and are also useful to lossy medium.     

Field solution in an anisotropic plasma imbedded in a moving dielectric medium

Wave equations in an anisotropic plasma imbedded in a moving dielectric medium have been derived through Maxwell-Minkowski relations. These are solved for longitudinal and transverse cases of propagation. The dispersion relation within the medium has been deduced through which the nature of splitting may be understood.     

TIME-DISTANCE HELIOSEISMOLOGY WITH THE MDI INSTRUMENT: INITIAL RESULTS

In time-distance helioseismology, the travel time of acoustic waves is measured between various points on the solar surface. To some approximation, the waves can be considered to follow ray paths that depend only on a mean solar model, with the curvature of the ray paths being caused by the increasing sound speed with depth below the surface. The travel time is affected by various inhomogeneities along the ray path, including flows, temperature inhomogeneities, and magnetic fields. By measuring a large number of times between different locations and using an inversion method, it is possible to construct 3-dimensional maps of the subsurface inhomogeneities. The SOI/MDI experiment on SOHO has several unique capabilities for time-distance helioseismology. The great stability of the images observed without benefit of an intervening atmosphere is quite striking. It has made it possible for us to detect the travel time for separations of points as small as 2.4 Mm in the high-resolution mode of MDI (0.6 arc sec pixel^-1). This has enabled the detection of the supergranulation flow. Coupled with the inversion technique, we can now study the 3-dimensional evolution of the flows near the solar surface.     

Qualitative analysis of cosmological models in Brans-Dicke theory

Isotropic and homogeneous cosmological models with a perfect fluid cource in Brans-Dicke theory are investigated from the point of view of dynamical system theory.Work partially supported by CNPq (Brazil).     

The Global, Local and Cluster Galaxy Luminosity Function

We review selected measurements of the galaxy luminosity function including the field, the local group, the local sphere, nearby clusters (Virgo, Coma and Fornax) and clusters in general. We conclude that, excluding the super-luminous cD and D galaxies, the overall cluster luminosity function is fully consistent with the field luminosity function over the magnitude range in common (–22 ≤ M _B –5log _{h 0.68} ≤ –17). We find that only in the core regions of clusters (r ≤ 300 kpc) does the overall form of the luminosity function show significant variation. However when the luminosity function is subdivided by spectral type some further variations are seen. We argue that these results imply: substantial late infall, efficient star-formation suppression, and the confinement of mass-changing evolutionary processes to the core regions only. This revised version was published online in July 2006 with corrections to the Cover Date.     

A research program to map the Galactic Emission at low frequencies

The need for accurate and complete maps of the galaxy at radio frequencies is made evident not only by the importance of the data in the study of galactic dynamics and structure formation but also in the analysis of cosmic background radiation data. A summary of the existing radio surveys of our galaxy is presented along with their limitations. A new program, the Galactic Emission Mapping (GEM) project, to obtain calibrated and complete maps of the galaxy in the 400 to 1400 MHz range, is outlined.Presented at the 2nd UN/ESA Workshop, held in Bogotá, Colombia, 9-13 November, 1992.     

DENIS: A deep near-infrared survey of the southern sky

The DENIS project is the first attempt to carry out a complete digitized survey of the southern sky in the range 1–2.5µm. The main objectives of the programme and the main specifications of the camera and of the data processing stream are briefly outlined