Type I Radio Bursts Deflected by Lower Hybrid Waves

Solar Physics - What are the observational effects if type I bursts are deflected by lower-hybrid waves? The deflection creates an elliptical radio mirage, with the direct source at one end of the...     

Circumstellar Silicate Mineralogy

This paper reviews spectra obtained with the SWS on board of ISO of dust shells around O-rich objects. These spectra reveal the presence of many new emission features between 10 and 45 μm. These bands are generally much narrower than the well-known 10 and 20 μm silicates features. The strength of these features relative to the underlying broad continuum varies from source to source (≅ 5-50%). The 10 μm region shows evidence for the presence of Al2O3 grains. At longer wavelength, the spectra are dominated by features due to crystalline olivine and pyroxene. The exact peak position of these features shows that the emitting grains consist of the Mg-rich end-members of these minerals with an Fe-content of < 10%. The underlying continuum is attributed to amorphous silicate grains. These observations of aluminum-rich and magnesium-rich compounds compare well with the thermodynamic condensation sequence of minerals expected for O-rich outflows. The observations also imply that freeze out (ie., kinetics) of this condensation sequence at different temperatures is an important characteristic of dust formation in these objects. It is suggested that the absence of Fe-rich silicates is a natural consequence of the low temperature at which gaseous Fe reacts with Mg-rich silicates in these outflows, resulting in amorphous grains with little characterizing spectral detail. This revised version was published online in August 2006 with corrections to the Cover Date.     

Exposure history of the Torino meteorite

Abstract— We determined He, Ne, Ar, ¹⁰Be, ²⁶Al, ³⁶Cl, and ¹⁴C concentrations, as well as cosmic-ray track densities and halogen concentrations in different specimens of the H6 chondrite Torino, in order to constrain its exposure history to cosmic radiation. The Torino meteoroid had a radius of ～20 cm and travelled in interplanetary space for 2.5–10 Ma. Earlier, Torino was part of a larger body. The smallest possible precursor had a radius of 55 cm and a journey through space longer than ～65 Ma. If the first-stage exposure took place in a body with a radius of >3 m or in the parent asteroid, then it lasted nearly 300 Ma. The example of Torino shows that it is easy to underestimate first-stage exposure ages when constructing two-stage histories.     

The radio and X-ray properties of Abell 2319

New radio and X-ray data are reported for the rich cluster Abell 2319. This object is known from optical data to consist of two separate clusters, which are displaced by about 10′ in the NW direction, and could be in a pre-merger state.

In the radio domain, the cluster is characterized by the presence of a central diffuse halo source, more extended and powerful than the prototype halo in the Coma cluster. The radio halo shows an irregular structure, elongated in the NE-SW direction, and also extended towards the NW. We also report data on the extended radio galaxies located within the halo, or in its proximity.

The cluster X-ray brightness distribution shows an elongated structure towards the NW, in the radial region between 6′–12′, i.e. in the direction of the subcluster. This feature is exactly coincident with the NW extension of the radio halo. In addition, more substructural features are identified which could be due to an ongoing merger of the cluster with yet another mass component.

The radio halo morphology is correlated with the X-ray structure and the existence of merger processes in the cluster. The cluster merger can provide energy to maintain the radio halo, while the origin of the relativistic particles seems more problematic.     

Rapid climatic changes recorded in loess successions

Detailed grain-size analyses, both in China and western Europe, indicate the occurrence of short climatic cycles during loess deposition of the last glacial. Cold episodes coincided with enhanced deposition of relatively coarse loess and alternated with relatively warmer episodes with decreased deposition of finer loess and soil formation. In Europe, these oscillations may coincide with alternations of permafrost development and degradation. The short-term climatic events in the loess sections are similar to the Dansgaard–Oeschger events in ice-core records.     

Stellar models and Hyades: the Hipparcos test

We compare theoretical stellar models for main sequence (MS) stars with the Hipparcos data base for the Hyades cluster to give a warning against the uncritical use of available theoretical scenarios and to show how formal MS fittings can be fortuitous if not fictitious. Moreover, we find that none of the current theoretical scenarios appears able to account for an observed mismatch between theoretical predictions and observations of the coolest Hyades MS stars. Finally, we show that current theoretical models probably give too faint He burning luminosities unlike the case of less massive He burning models, with degenerate progenitors, which have been suggested to suffer the opposite discrepancy.     

Simulations of deep pencil-beam redshift surveys

We create mock pencil-beam redshift surveys from very large cosmological N -body simulations of two cold dark matter (CDM) cosmogonies, an Einstein–de Sitter model ( τ CDM) and a flat model with Ω₀=0.3 and a cosmological constant (ΛCDM). We use these to assess the significance of the apparent periodicity discovered by Broadhurst et al. Simulation particles are tagged as 'galaxies' so as to reproduce observed present-day correlations. They are then identified along the past light-cones of hypothetical observers to create mock catalogues with the geometry and the distance distribution of the Broadhurst et al. data. We produce 1936 (2625) quasi-independent catalogues from our τ CDM (ΛCDM) simulation. A couple of large clumps in a catalogue can produce a high peak at low wavenumbers in the corresponding one-dimensional power spectrum, without any apparent large-scale periodicity in the original redshift histogram. Although the simulated redshift histograms frequently display regularly spaced clumps, the spacing of these clumps varies between catalogues and there is no 'preferred' period over our many realizations. We find only a 0.72 (0.49) per cent chance that the highest peak in the power spectrum of a τ CDM (ΛCDM) catalogue has a peak-to-noise ratio higher than that in the Broadhurst et al. data. None of the simulated catalogues with such high peaks shows coherently spaced clumps with a significance as high as that of the real data. We conclude that in CDM universes, the regularity on a scale of ∼130  h ⁻¹ Mpc observed by Broadhurst et al. has a priori probability well below 10⁻³.