Clustering of galaxy clusters in cold dark matter universes

We use very large cosmological N -body simulations to obtain accurate predictions for the two-point correlations and power spectra of mass-limited samples of galaxy clusters. We consider two currently popular cold dark matter (CDM) cosmogonies, a critical density model ( τ CDM) and a flat low density model with a cosmological constant (ΛCDM). Our simulations each use 10⁹ particles to follow the mass distribution within cubes of side 2  h ⁻¹ Gpc ( τ CDM) and 3  h ⁻¹ Gpc (ΛCDM) with a force resolution better than 10⁻⁴ of the cube side. We investigate how the predicted cluster correlations increase for samples of increasing mass and decreasing abundance. Very similar behaviour is found in the two cases. The correlation length increases from     for samples with mean separation     to     for samples with     The lower value here corresponds to τ CDM and the upper to ΛCDM. The power spectra of these cluster samples are accurately parallel to those of the mass over more than a decade in scale. Both correlation lengths and power spectrum biases can be predicted to better than 10 per cent using the simple model of Sheth, Mo & Tormen. This prediction requires only the linear mass power spectrum and has no adjustable parameters. We compare our predictions with published results for the automated plate measurement (APM) cluster sample. The observed variation of correlation length with richness agrees well with the models, particularly for ΛCDM. The observed power spectrum (for a cluster sample of mean separation     ) lies significantly above the predictions of both models.     

Non-linear amplification of a magnetic field driven by cosmic ray streaming

One-, two- and three-dimensional numerical results of the non-linear interaction between cosmic rays and a magnetic field are presented. These show that cosmic ray streaming drives large-amplitude Alfvénic waves. The cosmic ray streaming energy is very efficiently transferred to the perturbed magnetic field of the Alfvén waves, and the non-linear time-scale of the growth of the waves is found to be very rapid, of the order of the gyro-period of the cosmic ray. Thus, a magnetic field of interstellar values, assumed in models of supernova remnant blast wave acceleration, would not be appropriate in the region of the shock. The increased magnetic field reduces the cosmic ray acceleration time and so increases the maximum cosmic ray energy, which may provide a simple and elegant resolution to the highest energy Galactic cosmic ray problem, where the cosmic rays themselves provide the fields necessary for their acceleration.     

New views of Betelgeuse: multi-wavelength surface imaging and implications for models of hotspot generation

We report contemporaneous multi-wavelength interferometric imaging of the red supergiant star Betelgeuse ( α Orionis), using the Cambridge Optical Aperture Synthesis Telescope (COAST) and the William Herschel Telescope (WHT), at wavelengths of 700, 905 and 1290 nm. We find a strong variation in the apparent symmetry of the stellar brightness distribution as a function of wavelength. At 700 nm the star is highly asymmetric, and can be modelled as the superposition of three bright spots on a strongly limb-darkened disc. However, at 905 nm only a single low-contrast feature is visible and at 1290 nm the star presents a featureless symmetric disc. The change in spot contrast with wavelength is consistent with a model in which the bright spots represent unobscured areas of elevated temperature, owing perhaps to convection, on a stellar disc that itself has a different appearance, i.e. geometrical extent and limb-darkening profile, at different wavelengths. The featureless centre-to-limb brightness profile seen at 1290 nm is consistent with this model and suggests that future interferometric monitoring of the star to quantify the size changes associated with radial velocity variations should be performed at similar wavelengths in the near-infrared.     

Variations of the neutralino elastic cross-section with CP-violating phases

We analyze the neutralino–nucleus elastic cross-section in the minimal supersymmetric extension of the standard model (MSSM), including contributions from CP-violating phases, using the four-fermi neutralino–quark interaction. Over a wide range of the MSSM parameter space, we show the variations in the cross-sections due to these phases. We further concentrate on the regions which are consistent with constraints from the electric dipole moment of the electron, neutron and mercury atom. In the regions we examine in detail, we find suppressions by up to a factor of two, while enhancements in the cross-sections are no greater than 10%.     

Discovery of a flare star near Sirius

The discovery of a flare star (R.A. (1950)=6^h43^m6^s.07, Decl.(1950)=?16°45′24″) located about 6 arc min south of Sirius is reported. During photometric observations on the night of 13 January, 1982, using the 102 cm telescope at Kavalur, India, the star was seen to brighten by 2.55 mag. inV band over a duration of about 200 s. Observations on this object for a duration of about 10.5 hr spread over seven more nights indicate the star to be variable. The results of these observations are presented.     

Cosmic-ray antimatter: A primary origin hypothesis

We examine the possibility that the observed cosmic-ray protons are of primary extragalactic origin. The present \(\bar p\) data are consistent with a primary extragalactic component having \(\bar p\) /p?3.2±0.7 x 10^-4 independent of energy. Following the suggestion that most extragalactic cosmic rays are from active galaxies, we propose that most of the observed \(\bar p\) 's are alos from the same sites. This would imply the possibility of destroying the corresponding \(\bar \alpha \) 'sat the source, thus leading to a flux ratio \(\bar \alpha \) /α< \(\bar p\) /p. We further predict an estimate for \(\bar \alpha \) α～10^-5, within the range of future cosmic-ray detectors. the cosmological implications of this proposal are discussed.     

Regularization and linearization of the equations of motion in central force-fields

Within the framework of linear and regular celestial mechanics, a wide class of central force field problems are considered. We take as potential function a polynomial whose variable is the reciprocal of the distance from the origin, and, as regularizing function the square root of a certain reciprocal polynomial, related to the potential function. The relations between the coefficients of both functions, in order to arrive to linear equations, are given. In particular, the case of a quintic polynomial is analyzed, and an application is made to artificial earth satellites considering harmonicsJ ₂,J ₃,J ₄.     

The 12C/13C ratio in jupiter from the Voyager infrared investigation

The ¹²C/¹³C ratio in Jupiter has been derived from the analysis of the ν₄ band of CH₄ in the spectra recorded by the Voyager 1 IRIS experiment. It is found to be 160_?55⁺⁴⁰, i.e., 1.8_?0.6^+0.4 times the terrestrial value. Instrumental noise as well as systematic sources of error were taken into account for the estimate of the uncertainty. No plausible theory predicts such a difference between the values of the ¹²C/¹³C ratio in the inner solar system and in Jupiter. However, values of this ratio in the solar neighborhood 4.5 by ago inferred—through the use of models of chemical evolution of the Galaxy —from recent interstellar medium measurements are compatible with the present determination in Jupiter. The Jovian value, rather than the terrestrial one, could then be representative of the ratio in the primitive solar nebula.