Rapid rotation,active nests of convection and global-scale flows in solar-likestars

In the solar convection zone, rotation couples with intensely turbulent convection to build global-scale flows of differential rotation and meridional circulation. Our sun must have rotated more rapidly in its past, as is suggested by observations of many rapidly rotating young solar-type stars. Here we explore the effects of more rapid rotation on the patterns of convection in such stars and the global-scale flows which are self-consistently established. The convection in these systems is richly time dependent and in our most rapidly rotating suns a striking pattern of spatially localized convection emerges. Convection near the equator in these systems is dominated by one or two patches of locally enhanced convection, with nearly quiescent streaming flow in between at the highest rotation rates. These active nests of convection maintain a strong differential rotation despite their small size. The structure of differential rotation is similar in all of our more rapidly rotating suns, with fast equators and slower poles. We find that the total shear in differential rotation, as measured by latitudinal angular velocity contrast, ΔΩ, increases with more rapid rotation while the relative shear, ΔΩ/Ω, decreases. In contrast, at more rapid rotation the meridional circulations decrease in both energy and peak velocities and break into multiple cells of circulation in both radius and latitude. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Turbulent viscosity and Λ-effect from numerical turbulence models

Homogeneous anisotropic turbulence simulations are used to determine off-diagonal components of the Reynolds stress tensor and its parameterization in terms of turbulent viscosity and Λ-effect. The turbulence is forced in an anisotropic fashion by enhancing the strength of the forcing in the vertical direction. The Coriolis force is included with a rotation axis inclined relative to the vertical direction. The system studied here is significantly simpler than that of turbulent stratified convection which has often been used to study Reynolds stresses. Certain puzzling features of the results for convection, such as sign changes or highly concentrated latitude distributions, are not present in the simpler system considered here. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Weakly relativistic solitary waves in multicomponent plasmas with electron inertia

Existence of compressive relativistic solitons is established in an arbitrary ξ-direction, inclining at an angle to the direction of the weak magnetic field (ω _pi ≫ω _Bi ) in this plasma compound with ions, relativistic electrons and relativistic electron beams. It is observed that the absolute linear growth of amplitudes of compressive solitons is due to inactive role of the weak magnetic field and the initial streaming speeds of relativistic electrons, electron beams, and Q _b (ion mass to electron beam mass). Besides, the small initial streaming of electrons is found to be responsible to generate relatively high amplitude compressive solitons. The non-relativistic ions in the background plasma, but in absence of electron-beam drift and in presence of weak magnetic field are the causing effect of interest for the smooth growth of soliton amplitudes in this model of plasma.     

Spin down of rotating compact magnetized strange stars in general relativity

We find that in general relativity slow down of the pulsar rotation due to the magnetodipolar radiation is more faster for the strange star with comparison to that for the ordinary neutron star of the same mass. Comparison with astrophysical observations on pulsars spindown data may provide an evidence for the strange star existence and, thus, serve as a test for distinguishing it from the neutron star.     

Electromagnetic fields in jets

The magnetic fields and energy flows in an astronomical jet described by our earlier model are calculated in detail. Though the field distribution varies with the external pressure function   p ( z )  , it depends only weakly on the other boundary conditions. Individual field lines were plotted; the lines become nearly vertical at the bottom and are twisted at the top. An animation of a field line's motion was made, which shows the line being wound up by the accretion disc's differential rotation and rising as a result of this. The distribution of Poynting flux within the jet indicates that much of the energy flows up the jet from the inside of the accretion disc but a substantial fraction flows back down to the outside.     

The environments and clustering properties of 2dF Galaxy Redshift Survey selected starburst galaxies

We investigate the environments and clustering properties of starburst galaxies selected from the 2dF Galaxy Redshift Survey (2dFGRS) in order to determine which, if any, environmental factors play a role in triggering a starburst. We quantify the local environments, clustering properties and luminosity functions of our starburst galaxies and compare to random control samples. The starburst galaxies are also classified morphologically in terms of their broad Hubble type and evidence of tidal merger/interaction signatures. We find the starburst galaxies to be much less clustered on large (5–15 Mpc) scales compared to the overall 2dFGRS galaxy population. In terms of their environments, we find just over half of the starburst galaxies to reside in low to intermediate luminosity groups, and a further ∼30 per cent residing in the outskirts and infall regions of rich clusters. Their luminosity functions also differ significantly from that of the overall 2dFGRS galaxy population, with the sense of the difference being critically dependent on the way their star formation rates are measured. In terms of pin-pointing what might trigger the starburst, it would appear that factors relating to their local environment are most germane. Specifically, we find clear evidence that the presence of a near neighbour of comparable luminosity/mass within 20 kpc is likely to be important in triggering a starburst. We also find that a significant fraction (20–30 per cent) of the galaxies in our starburst samples have morphologies indicative of either an ongoing or a recent tidal interaction and/or merger. These findings notwithstanding, there remain a significant portion of starburst galaxies where such local environmental influences are not in any obvious way playing a triggering role, leading us to conclude that starbursts can also be internally driven.