On the most general accurate solutions for Buchdahl's fluid spheres

The most general accurate solutions for the Buchdhal fluid sphere were obtained and matched with the Schwarzchild's exterior solution at the pressure free interface. Various parameters of the solutions were so adjusted that the energy density, pressure and temperature were positive and decreasing away from the centre, and the velocity of sound was less than unity throughout the spheroid model. Using this procedure, the maximum mass of the fluid sphere with a surface density of2 × 10¹⁴gm cm^-3 was determined to be 3.82MΘ and 4.57 MΘ for strong and weak energy conditions respectively. PACS number: 0402, 0402J, 0440D, 95301 This revised version was published online in July 2006 with corrections to the Cover Date.     

Kinematics in the z = 2.81 Galaxy and the Evidence for Rotation

The existence of rotation signatures in damped Lyαabsorption systems represents a crucial test of the hypothesis that these features arise in disks of normal spiral galaxies. We apply the method for evaluating such signatures to the metal absorption lines in QSO 0528-250. In particular, the systemic redshift of the absorber is inferred from the recent detection of emission in the absorber by Möller and Warren. The kinematics of this absorber are particularly interesting because molecular hydrogen, the densest ISM component of the assumed foreground absorbing galaxy, is detected. Contrary to a recent claim, the method yields a satisfactory value for the assumed rotation velocity of the absorber.     

Evidence for a mid‐Pleistocene shift of ice‐drift pattern in the Nordic seas

Sediment proxy records from a continuous, 1.5 million year long deep‐sea sediment core from a site in the western Norwegian Sea were used to obtain new insights into the nature of palaeoceanographic change in the northern North Atlantic (Nordic seas) during the climatic shift of the Mid‐Pleistocene Revolution (MPR). Red‐green sediment colour and magnetic susceptibility records both reveal significant differences in their mean values when comparing the intervals older than 700 000 yr (700 ka) with those from the past 500 kyr. The timing and duration of these changes indicates that the MPR in the Nordic seas is characterised by a gradual transition lasting about 200 kyr. Together with further sedimentological evidence this suggests that the mid‐Pleistocene climate shift was accompanied by a general change in ice‐drift pattern. It is further proposed that prior to the onset of the major late Pleistocene glaciations in the Northern Hemisphere a significant proportion of the ice in the eastern Nordic seas originated from a southern provenance, whereas later it dominantly came from the surrounding landmasses. Copyright © 2003 John Wiley & Sons, Ltd.     

Microtextures and crystal chemistry in P21/c pigeonites

Summary ?A single-crystal X-ray investigation was performed on crystals of P2₁/c natural pigeonite with varying Ca and Fe^* ( = Fe²⁺ + Mn²⁺) contents, in order to verify the effect of microtextural disorder on structure refinements and to constrain the crystal chemistry of pigeonite. Antiphase domains and exsolution lamellae affect differently the refinement results. In a crystal free of exsolution the structure obtained after refinement with all reflections is an average of that of the antiphase domains and of their boundaries, whereas in an exsolved crystal it represents only the structure of the prevailing pigeonite lamellae. The refinement using only h + k odd reflections seems to give the structure of the Ca-free pigeonite characteristic of the antiphase domains rather than that of Ca-rich domain walls. The ratio of the scale factors in refinements with all reflections and with only h + k odd reflections allows the ratios of the exsolved augite and pigeonite phases to be estimated. The crystal chemistry of the investigated samples follows the trends outlined by data on Ca-free and Fe-free synthetic samples. In particular, it is shown that Ca and Fe^* substitution for Mg induce similar changes in the average structure, i.e. both induce an expansion in the M1 polyhedron and decrease the difference between the M2–O3 distances. Received October 18, 2001; revised version accepted February 15, 2002     

Morphology and Luminosity Segregations in Galaxy Groups

We study morphology and luminosity segregation of galaxies in groups. We analyze the two catalogs of (∼2×400) groups which have been identified in the Nearby Optical Galaxy sample, by means of hierarchical and percolation `friends-of-friends' methods. We find that earlier-type (brighter) galaxies are more clustered and lie closer to the group centers, both in position and in velocity, than later-type (fainter) galaxies. Spatial segregations are stronger than kinematical segregations. These effects are generally detected at the ≳3-sigma level, with the exception of morphological segregation in velocity, which is the weakest effect. Our main results are confirmed by the analysis of statistically more reliable groups (with at least five members), and are strengthened by the detection of segregation in both hierarchical and percolation catalogs. Luminosity segregation is shown to be independent of morphology segregation. Our conclusions agree with a continuum of segregation properties of galaxies in systems, from low-mass groups to massive clusters. This revised version was published online in July 2006 with corrections to the Cover Date.     

Photometric Study of the W Uma-Type Eclipsing Binary System GSC 4832.400

We present a photometric analysis of the eclipsing binary systemGSC4832.400 based on 732 photometric observations obtained on sixteen clear nights during 1999–2000 in the V-Johnson and yb-Strömgren filters. The observed times of the minima yielded a linear ephemeris showing that the system has a constant period of 0.313150 ± 0.000002days. The light curve corresponds to a circular orbit for the system and clearly shows that GSC4832.400 has the defining characteristics of a W UMa-type eclipsing binary. It also shows a small O'Connell effect, which could be due to the presence of a hot spot in the primary star. A preliminary photometric solution based on the assumption of an over contact systemsatis factorily reproduced the observed light curve.     

Plane Symmetric Domain Wall in Lyra Geometry

In this paper general solutions are found for domain walls in Lyra geometry in the plane symmetric spacetime metric given by Taub. Expressions for the energy density and pressure of domain walls are derived in both cases of uniform and time varying displacement field β. It is also shown that the results obtained by Rahaman et al [IJMPD, 10, 735 (2001)] are particular case of our solutions. Finally, the geodesic equations and acceleration of the test particle are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.