Non-existence of higher dimensional anisotropic cosmological model in bimetric theory of gravitation

A Five dimensional spherically symmetric space-time model in Rosen's (1973) bimetric theory of gravitation is considered. It is shown that, in this theory, the geometry of the five dimensional space-time does not admit perfect fluid source. Hence a vacuum model is presented and studied. It is observed that in the case of stiff fluid we again get the vacuum model. This revised version was published online in July 2006 with corrections to the Cover Date.     

Comet Halley's dust drag perturbing the Giotto spacecraft

Hypervelocity impact sputter causes impulses substantially greater than the initial momenta of micro-grains of comet Halley's dust coma, the effective factor being discontinuous at the dust mass (0.2 g) that just penetrates the spacecraft bumper shield. Marginally non-penetrating grains determine the net drag and torque, calculated here for the Giotto shield and exposed components. The torque due to asymmetries induces a precession of the spacecraft axis, whose amplitude is solved for passage through the model dust coma, to find slowly damped oscillations of significant (1°) amplitude.     

Star count of the North Galactic Pole region in theUBV colour bands

Astrophysics and Space Science -     

An anisotropic cosmological model in a scalar-tensor theory of gravitation

A spatially-homogeneous and anisotropic-cosmological model in a scalar-tensor theory proposed by Sen and Dunn (1971) is obtained when the source of the gravitational field is a perfect fluid with pressure equal to energy density and the metric is of Bianchi type-I. Various physical properties of the model have also been discussed.     

Doppler Images of ζ Andromedae

Doppler images are presented for the RS CVn-type binary ζ And. Our upgraded Doppler imaging code TempMap_ε takes into account the distorted geometry of the primary giant component. On the maps several low latitude spots are restored with a temperature contrast of about 1000 K. Some weak polar features are also found. Cross-correlation of the consecutive Doppler-maps suggests solar-like differential surface rotation.     

Mass composition of the escaping plasma at Mars

Data from the Ion Mass Analyzer (IMA) sensor of the ASPERA-3 instrument suite on Mars Express have been analyzed to determine the mass composition of the escaping ion species at Mars. We have examined 77 different ion-beam events and we present the results in terms of flux ratios between the following ion species: CO⁺₂/O⁺ and O⁺₂/O⁺. The following ratios averaged over all events and energies were identified: CO⁺₂/O⁺ = 0.2 and O⁺₂/O⁺ = 0.9. The values measured are significantly higher, by a factor of 10 for O⁺₂/O⁺, than a contemporary modeled ratio for the maximum fluxes which the martian ionosphere can supply. The most abundant ion species was found to be O⁺, followed by O⁺₂ and CO⁺₂. We estimate the loss of CO⁺₂ to be by using the previous measurements of Phobos-2 in our calculations. The dependence of the ion ratios in relation to their energy ranges we studied, 0.3-3.0 keV, indicated that no clear correlation was found.     

Evolution of the Fine Structure of Magnetic Fields in the Quiet Sun: Observations from Sunrise/IMaX and Extrapolations

Observations with the balloon-borne Sunrise/Imaging Magnetograph eXperiment (IMaX) provide high spatial resolution (roughly 100 km at disk center) measurements of the magnetic field in the photosphere of the quiet Sun. To investigate the magnetic structure of the chromosphere and corona, we extrapolate these photospheric measurements into the upper solar atmosphere and analyze a 22-minute long time series with a cadence of 33 seconds. Using the extrapolated magnetic-field lines as tracer, we investigate temporal evolution of the magnetic connectivity in the quiet Sun’s atmosphere. The majority of magnetic loops are asymmetric in the sense that the photospheric field strength at the loop foot points is very different. We find that the magnetic connectivity of the loops changes rapidly with a typical connection recycling time of about 3±1 minutes in the upper solar atmosphere and 12±4 minutes in the photosphere. This is considerably shorter than previously found. Nonetheless, our estimate of the energy released by the associated magnetic-reconnection processes is not likely to be the sole source for heating the chromosphere and corona in the quiet Sun.