Gravitational Lens Systems to probe Extragalactic Magnetic Fields

The Faraday rotation measurements of multiply-imaged gravitational lens systems can be effectively used to probe the existence of large-scale ordered magnetic fields in lensing galaxies and galaxy clusters. The available sample of lens systems appears to suggest the presence of a coherent large-scale magnetic field in giant elliptical galaxies somewhat similar to the spiral galaxies.Comment: 11 pages, 1 figur

On the inversion of the density gradient at the fringe of the convection zone

Introduction. It is well known that the total pressure and the temperature increase as one goes inward from the surface to the center of a star. That the density, on the other hand, does not necessarily increase with depth below the surface was pointed out by Hoyle and Schwarzschild (1955) and was borne out quite clearly by the numerical integrations of the solar surface layers by Faulkner, Griffiths, and Hoyle (1963). The question was raised by Tayler and Gough (1963) as to whether the density gradient inversion was real or whether it was due to the particular model of convection adopted by Faulkner et al. It is the purpose of this note to show that the inversion is indeed genuine and results from the steep temperature gradient that exists in the outermost layers of the convection zone where convection is not fully efficient and carries only a fraction (<1/2) of the total energy flux. Also, the electron pressure-temperature plane can be divided into regions where dp/dT is negative and positive. The dividing line depends, in an insensitive manner, on the assumed model and efficiency of convection. In the case of the sun it is the hydrogen ionization at about 10^4 °K that causes the opacity to go up sharply and as a result the temperature gradient steepens there by inverting the density gradient. The inversion necessarily results in a Rayleigh-Taylor instability

Does Viscosity turn inflation into the CMB and Λ\Lambda

Consideration of the entropy production in the creation of the CMB leads to a simple model of the evolution of the universe during this period which suggests a connection between the small observed acceleration term and the early inflation of a closed universe. From this we find an unexpected relationship between the Omega's of cosmology and calculate the total volume of the universe.Comment: 8 pages , 2 figure

Role of the scalar field in gravitational lensing

A static and circularly symmetric lens characterized by mass and scalar charge parameters is constructed. For the small values of the scalar charge to the mass ratio, the gravitational lensing is qualitatively similar to the case of the Schwarzschild lens; however, for large values of this ratio the lensing characteristics are significantly different. The main features are the existence of two or nil Einstein ring(s) and a radial critical curve, formation of two or four images and possibility of detecting three images near the lens for sources located at relatively large angular positions. Such a novel lens may also be treated as a naked singularity lens.Comment: 11 pages using A&A LaTex, 3 figures included, misprints corrected, changes in section five, two references added Journal- ref : Astronomy & Astrophysics, 337(1) 1 (1998

Solar internal rotation rate and the latitudinal variation of the tachocline

A new set of accurately measured frequencies of solar oscillations are used to infer the rotation rate inside the Sun, as a function of radial distance as well as latitude. We have adopted a regularized least squares technique with iterative refinement for both 1.5D inversion using the splitting coefficients and 2D inversion using individual m splittings. The inferred rotation rate agrees well with earlier estimates showing a shear layer just below the surface and another one around the base of the convection zone. The tachocline or the transition layer where the rotation rate changes from differential rotation in the convection zone to almost latitudinally independent rotation rate in the radiative interior is studied in detail. No compelling evidence for any latitudinal variation in position and width of tachocline is found though it appears that the tachocline probably shifts to slightly larger radial distance at higher latitudes and possibly becomes thicker also. However, these variations are within the estimated errors and more accurate data would be needed to make a definitive statement about latitudinal variations.Comment: 15 pages, MNRAS-TeX, 15 figure

The Case of missing solar neutrinos with their split personalities

This article does not have an abstract

On the magnetic field required for driving the observed angular-velocity variations in the solar convection zone

A putative temporally varying circulation-free magnetic-field configuration is inferred in an equatorial segment of the solar convection zone from the helioseismologically inferred angular-velocity variation, assuming that the predominant dynamics is angular acceleration produced by the azimuthal Maxwell stress exerted by a field whose surface values are consistent with photospheric line-of-sight measurements.Comment: to appear in MNRA

Perspectives on the interior of the Sun

The interior of the Sun is not directly accessible to observations. Nonetheless, it is possible to infer the physical conditions inside the Sun with the help of structure equations governing its equilibrium and with the powerful observational tools provided by the neutrino fluxes and oscillation frequencies. The helioseismic data show that the internal constitution of the Sun can be adequately represented by a standard solar model. It turns out that a cooler solar core is not a viable solution for the measured deficit of neutrino fluxes, and the resolution of the solar neutrino puzzle should be sought in the realm of particle physics

Seismic tests for solar models with tachocline mixing

We have computed accurate 1-D solar models including both a macroscopic mixing process in the solar tachocline as well as up-to-date microscopic physical ingredients. Using sound speed and density profiles inferred through primary inversion of the solar oscillation frequencies coupled with the equation of thermal equilibrium, we have extracted the temperature and hydrogen abundance profiles. These inferred quantities place strong constraints on our theoretical models in terms of the extent and strength of our macroscopic mixing, on the photospheric heavy elements abundance, on the nuclear reaction rates such as $S_{11}$ and $S_{34}$ and on the efficiency of the microscopic diffusion. We find a good overall agreement between the seismic Sun and our models if we introduce a macroscopic mixing in the tachocline and allow for variation within their uncertainties of the main physical ingredients. From our study we deduce that the solar hydrogen abundance at the solar age is $X_{\rm inv}=0.732\pm 0.001$ and that based on the $^9$Be photospheric depletion, the maximum extent of mixing in the tachocline is 5% of the solar radius. The nuclear reaction rate for the fundamental $pp$ reaction is found to be $S_{11}(0)=4.06\pm 0.07$ $10^{-25}$ MeV barns, i.e., 1.5% higher than the present theoretical determination. The predicted solar neutrino fluxes are discussed in the light of the new SNO/SuperKamiokande results.Comment: 16 pages, 12 figures, A&A in press (1) JILA, University of Colorado, Boulder, CO 80309-0440, USA, (2) LUTH, Observatoire de Paris-Meudon, 92195 Meudon, France, (3) Tata Institute of Fundamental Research, Homi Bhabha road, Mumbai 400005, India, (4) Department of Physics, University of Mumbai, Mumbai 400098, Indi