The evolution of bodies orbiting in the trans-Neptunian region on to intermediate-type orbits

We investigate the dynamical evolution of 210 hypothetical massless bodies initially situated between 10 and 30 au from the Sun in order to determine the general characteristics of the evolved system. This is of particular relevance to the understanding of the origin of Edgeworth–Kuiper belt objects on scattered intermediate orbits, such as 1996 TL ₆₆, which have high eccentricity and semimajor axis but nevertheless have perihelion in the region between 30 and 50 au from the Sun.     

Neural networks and the separation of cosmic microwave background and astrophysical signals in sky maps

We implement an independent component analysis (ICA) algorithm to separate signals of different origin in sky maps at several frequencies. Owing to its self-organizing capability, it works without prior assumptions on either the frequency dependence or the angular power spectrum of the various signals; rather, it learns directly from the input data how to identify the statistically independent components, on the assumption that all but, at most, one of the components have non-Gaussian distributions.
We have applied the ICA algorithm to simulated patches of the sky at the four frequencies (30, 44, 70 and 100 GHz) used by the Low Frequency Instrument of the European Space Agency's Planck satellite. Simulations include the cosmic microwave background (CMB), the synchrotron and thermal dust emissions, and extragalactic radio sources. The effects of the angular response functions of the detectors and of instrumental noise have been ignored in this first exploratory study. The ICA algorithm reconstructs the spatial distribution of each component with rms errors of about 1 per cent for the CMB, and 10 per cent for the much weaker Galactic components. Radio sources are almost completely recovered down to a flux limit corresponding to ≃0.7 σ _CMB, where σ _CMB is the rms level of the CMB fluctuations. The signal recovered has equal quality on all scales larger than the pixel size. In addition, we show that for the strongest components (CMB and radio sources) the frequency scaling is recovered with per cent precision. Thus, algorithms of the type presented here appear to be very promising tools for component separation. On the other hand, we have been dealing here with a highly idealized situation. Work to include instrumental noise, the effect of different resolving powers at different frequencies and a more complete and realistic characterization of astrophysical foregrounds is in progress.     

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.     

On measuring low-degree p-mode frequency splitting with full-disc integrated data

The standard method of measuring rotational splitting from solar full-disc oscillation data, based on maximum-likelihood fitting of multi-Lorentzian profiles to oscillation power spectra, systematically overestimates the splitting. One of the reasons is that the maximum likelihood estimators (MLE) become unbiased only asymptotically as the number of data tends to infinity; for a finite data set they are often biased, inducing a systematic error. In this paper we assess by Monte Carlo simulations the amount of systematic error in the splitting measurement, using artificially generated power spectra. The simulations are carried out for multiplets of degree     2 and 3 with various signal-to-noise ratios, linewidths and observing times. We address the possible use of non-MLE estimators that could provide a smaller or negligible systematic error. The implication for asteroseismology is also discussed.     

Companions and interactions in the NGC 6946 system

We report the results of a survey of the H  i environment of NGC 6946 in a search for gas-rich companions to the galaxy. Such gas-rich companions could include material left over from the galaxy assembly process which could persist into the current day around an isolated galaxy such as NGC 6946. NGC 6946 is prolifically forming stars, has a nuclear starburst, and has widespread high-velocity clouds associated with the disc. All of these features could be explained by the accretion of low-mass H  i clouds by NGC 6946. Our survey recovered two previously detected dwarf galaxies associated with NGC 6946, but otherwise found no signatures of interactions in the NGC 6946 system. The companions are small enough, and distant enough from NGC 6946 that they should have minimal effect on the main galaxy. Some tidal debris may be expected due to interaction between the two dwarf galaxies, but none is observed. This could be because it is at low column densities, or because the dwarf galaxies are more separated than they appear on the sky. This study of the system suggests that NGC 6946 is a gravitationally bound system with two dwarf galaxies in stable orbits about the larger primary galaxy.     

Thermal and kinematic corrections to the microwave background polarization induced by galaxy clusters along the line of sight

We derive analytic expressions for the leading-order corrections to the polarization induced in the cosmic microwave background (CMB) owing to scattering of photons off hot electrons in galaxy clusters along the line of sight. For a thermal distribution of electrons with kinetic temperature k _B T _e∼10 keV and bulk peculiar velocity V ∼1000 km s⁻¹, the dominant corrections to the polarization induced by the primordial CMB quadrupole and the cluster peculiar velocity arise from electron thermal motion and are at the level of ∼10 per cent in each case, near the peak of the polarization signal. When more sensitive measurements become feasible, these effects will be significant for the determination of transverse peculiar velocities, and the value of the CMB quadrupole at the cluster redshift, via the cluster polarization route.     

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.     

Collimation of extragalactic radio jets in compact steep-spectrum and larger sources

We study the collimation of radio jets in the high-luminosity Fanaroff–Riley class II sources by examining the dependence of the sizes of hotspots and knots in the radio jets on the overall size of the objects for a sample of compact steep-spectrum (CSS) and larger-sized objects. The objects span a wide range in overall size from about 50 pc to nearly 1 Mpc. The mean size of the hotspots increases with the source size during the CSS phase, which is typically taken to be about 20 kpc, and the relationship flattens for the larger sources. The sizes of the knots in the compact as well as the larger sources are consistent with this trend. We discuss possible implications of these trends. We find that the hotspot closer to the nucleus or core component tends to be more compact for the most asymmetric objects where the ratio of separations of the hotspots from the nucleus r _d>2. These highly asymmetric sources are invariably CSS objects, and their location in the hotspot size ratio–separation ratio diagram is possibly the result of their evolution in an asymmetric environment. We also suggest that some sources, especially of lower luminosity, exhibit an asymmetry in the collimation of the oppositely directed radio jets.     

Climate sensitivity to changes in land surface characteristics

Using a recently developed global vegetation distribution, topography, and shorelines for the Early Eocene in conjunction with the Genesis version 2.0 climate model, we investigate the influences that these new boundary conditions have on global climate. Global mean climate changes little in response to the subtle changes we made; differences in mean annual and seasonal surface temperatures over northern and southern hemispheric land, respectively, are on the order of 0.5°C. In contrast, and perhaps more importantly, continental scale climate exhibits significant responses. Increased peak elevations and topographic detail result in larger amplitude planetary 4 mm/day and decreases by 7–9 mm/day in the proto Himalayan region. Surface temperatures change by up to 18°C as a direct result of elevation modifications. Increased leaf area index (LAI), as a result of altered vegetation distributions, reduces temperatures by up to 6°C. Decreasing the size of the Mississippi embayment decreases inland precipitation by 1–2 mm/day. These climate responses to increased accuracy in boundary conditions indicate that “improved” boundary conditions may play an important role in producing modeled paleoclimates that approach the proxy data more closely.