Bianchi type-VI0 conformally invariant scalar fields

An exact solution of Einstein's equations corresponding to the conformally invariant scalar field with tracefree energy-momentum tensor as source is obtained in Bianchi type VI₀ class of metrics. The solution represents a spatially homogeneous but anisotropy universe which admits anisotropic expansions. Some properties of the cosmological model are discussed.     

The effect of Main-Sequence stars on age estimates of open clusters

Existing methods for age estimation of open clusters are discussed. Most of the observed open clusters (except extremely young and old) contain 50–90% unevolved Main-Sequence stars. Possible difficulties encountered in estimating the actual age of an unevolved Main-Sequence star are discussed. For a relatively reliable cluster age estimation only a small percentage of cluster members are suitable. The effect of unevolved Main-Sequence stars on open cluster age estimates using the modified method of isochromes is analyzed.On leave of absence from the Department of Physics, Kumaon University, Naini Tal, India.     

Existence of equilibrium points and their linear stability in the generalized photogravitational Chermnykh-like problem with power-law profile

We consider the modified restricted three body problem with power-law density profile of disk, which rotates around the center of mass of the system with perturbed mean motion. Using analytical and numerical methods, we have found equilibrium points and examined their linear stability. We have also found the zero velocity surface for the present model. In addition to five equilibrium points there exists a new equilibrium point on the line joining the two primaries. It is found that L ₁ and L ₃ are stable for some values of inner and outer radius of the disk while other collinear points are unstable, but L ₄ is conditionally stable for mass ratio less than that of Routh’s critical value. Lastly, we have studied the effects of radiation pressure, oblateness and mass of the disk on the motion and stability of equilibrium points.     

Effect of electron temperature on small-amplitude electron acoustic solitary waves in non-planar geometry

Effects of electron temperature on the propagation of electron acoustic solitary waves in plasma with stationary ions, cold and superthermal hot electrons is investigated in non-planar geometry employing reductive perturbation method. Modified Korteweg–de Vries equation is derived in the small amplitude approximation limit. The analytical and numerical calculations of the KdV equation reveal that the phase velocity of the electron acoustic waves increases as one goes from planar to non planar geometry. It is shown that the electron temperature ratio changes the width and amplitude of the solitary waves and when electron temperature is not taken into account,our results completely agree with the results of Javidan & Pakzad (2012). It is found that at small values of \(\tau \), solitary wave structures behave differently in cylindrical (\(\text {m} = 1\)), spherical (\(\text {m} = 2\)) and planar geometry (\(\text {m} = 0\)) but looks similar at large values of \(\tau \). These results may be useful to understand the solitary wave characteristics in laboratory and space environments where the plasma have multiple temperature electrons.     

Quasi-similar solution of the strong shock wave problem in non-ideal gas dynamics

The quasisimilar theory is used to investigate the solution of the blast wave problem with generalized geometries in a non-ideal gas satisfying the equation of state of the Van der Waals type. Here it is assumed that the distribution of normalized velocity, pressure and density are nearly similar in the narrow range of the shock strength. A comparison between approximate analytical solution and numerical solution of the problem is presented for the cylindrical geometry. The numerical solutions are presented for the generalized geometry in a non-ideal gas. It is also assessed as to how the non-idealness of the gas affects the behavior of the flow parameters.     

On the Photometric Error Calibration for the Differential Light Curves of Point-like Active Galactic Nuclei

It is important to quantify the underestimation of rms photometric errors returned by the commonly used APPHOT algorithm in the IRAF software, in the context of differential photometry of point-like AGN, because of the crucial role it plays in evaluating their variability properties. Published values of the underestimation factor, η, using several different telescopes, lie in the range 1.3–1.75. The present study aims to revisit this question by employing an exceptionally large data set of 262 differential light curves (DLCs) derived from 262 pairs of non-varying stars monitored under our ARIES AGN monitoring program for characterizing the intra-night optical variability (INOV) of prominent AGN classes. The bulk of these data were taken with the 1-m Sampurnanad Telescope (ST). We find η?=?1.54±0.05 which is close to our recently reported value of η?=?1.5. Moreover, this consistency holds at least up to a brightness mismatch of 1.5 mag between the paired stars. From this we infer that a magnitude difference of at least up to 1.5 mag between a point-like AGN and comparison star(s) monitored simultaneously is within the same CCD chip acceptable, as it should not lead to spurious claims of INOV.     

Finite-difference analysis of the MHD stokes problem for a vertical plate with Hall and ion-slip currents

An explicit finite-difference method is employed to study the MHD free convection heat generating fluid past an impulsively started vertical infinite plate when a strong magnetic field is applied perpendicular to the plate. The velocity and temperature profiles are shown on graphs and the results are discussed in terms of the non-dimensional parameters _e (Hall parameter), _i (ionslip parameter), (heat source parameter), and Gr (Grashof number).     

Radial distribution of the integrated light and photometric colours in open star clusters

Mass segregation in the form of preferential concentration of more massive stars in the central regions of a number of open star clusters has been known for some time. In this paper, integratedUBV colours in concentric zones have been estimated for 12 nearby open clusters using the observations of individual cluster members. It is found that the clusters showing pronounced mass segregation also show significant radial variations in the integrated colours. However, the effects of stochastic fluctuations around the massive portion of the mass distribution function on the integrated colours should be taken into consideration, if they are present.     

Radial clastic dykes formed by a salt diapir in the Dead Sea Rift, Israel

ABSTRACT Fanning structures radiating from a central perturbation are known in various geological environments, where different processes have produced similar geometry. The present contribution describes and analyses fanning clastic dykes in the Dead Sea Rift, a new example of diapir-related deformation. The dykes are opening-mode fractures exposed in lacustrine varved marl of the Lisan Formation, deposited 70–15 ka. They are arranged mainly in a radial and tangential geometry. The radial traces converge at the 'Black Hill' structural dome. The geometry of the fractures is consistent with stresses exerted by the rise of a salt diapir located underneath the Black Hill. The estimated extension of the radial fractures is in good agreement with the present topographic elevation of the hill. The absence of fractures in the overlying Holocene alluvium probably indicates that either the rise of the Black Hill salt diapir paused or is associated now with a different style of deformation.