High-energy particle acceleration and production of ultra-high-energy cosmic rays in the giant lobes of Centaurus A

The nearby radio galaxy Centaurus A is poorly studied at high frequencies with conventional radio telescopes because of its very large angular size, but is one of a very few extragalactic objects to be detected and resolved by the Wilkinson Microwave Anisotropy Probe ( WMAP ). We have used the five-year WMAP data for Cen A to constrain the high-frequency radio spectra of the 10° giant lobes and to search for spectral changes as a function of position along the lobes. We show that the high-frequency radio spectra of the northern and southern giant lobes are significantly different: the spectrum of the southern lobe steepens monotonically (and is steeper further from the active nucleus) whereas the spectrum of the northern lobe remains consistent with a power law. The inferred differences in the northern and southern giant lobes may be the result of real differences in their high-energy particle acceleration histories, perhaps due to the influence of the northern middle lobe, an intermediate-scale feature which has no detectable southern counterpart. In light of these results, we discuss the prospects for Fermi Gamma-ray Space Telescope detections of inverse-Compton emission from the giant lobes and the lobes' possible role in the production of the ultra-high-energy cosmic rays (UHECR) detected by the Pierre Auger Observatory. We show that the possibility of a Fermi detection depends sensitively on the physical conditions in the giant lobes, with the northern lobe more likely to be detected, and that any emission observed by Fermi is likely to be dominated by photons at the soft end of the Fermi energy band. On the other hand, we argue that the estimated conditions in the giant lobes imply that UHECRs can be accelerated there, with a potentially detectable γ-ray signature at TeV energies.     

Short-period Jupiter family comets after Stardust

The NASA Stardust mission has provided for laboratory study an extensive data set of cometary dust of known provenance (from comet 81P/Wild 2) yielding detailed insights into the composition of the comet. Combined with the results of data from other missions to short-period Jupiter family comets (JFC), this has greatly deepened the understanding of such objects. If depressions on the surface of comet 81P/Wild 2 are all taken as evidence of impact cratering, their number suggests a long occupancy in the outer region of the Solar System. The dust from comet 81P/Wild 2 has been shown to be heavily deficient in pre-Solar grains and rich in materials formed at high temperatures in the inner Solar System. Although it is too early to know if this is typical of JFC, it does argue for rapid and thorough mixing of materials in the disk on timescales related to comet formation, and may also suggest outward migration of small icy bodies after their formation. Thus, instead of providing mainly new knowledge of the pre-Solar materials expected to be rich in comets, Stardust and comet 81P/Wild 2 have instead focussed attention on large-scale transport processes during the critical period when cometary parent bodies were forming in the early Solar System.     

Linking Remote-Sensing and <Emphasis Type="Italic">In Situ</Emphasis> Observations of Coronal Mass Ejections Using STEREO

The twin STEREO spacecraft have been observing the Sun since 2006. Even though STEREO has only been active during solar minimum conditions so far, an important number of coronal mass ejections (CMEs) and their interplanetary counterparts (ICMEs) have been observed. Many of the ICMEs can be linked back to the corresponding CMEs on the Sun through the combination of remote-sensing and in situ observations. This paper aims to answer the question whether a CME observed by a coronagraph will be detected in situ by a spacecraft in a specific location in the heliosphere. We use a flux-rope-like model fit to the STEREO SECCHI/COR2 data to obtain the direction of CME propagation and its geometrical configuration in three dimensions. Based on model parameters, we then calculate their angular widths and determine whether they should have been detected by STEREO-A, STEREO-B, Wind or ACE. We compare the results with corresponding in situ observations of ICMEs. We find that predictions of ICME detections on the base of COR2 data generally match well the actual in situ observations.     

OSO-8 observations of CaII H and K,MgII h and k,Lα and Lβ above a sunspot

Observations with the French (L.P.S.P.) experiment on board OSO-8 of a sunspot and nearby plage region are described. The behaviour of the emission cores of the Ca II H and K and Mg II h and k resonance lines is very similar and the correspondence in intensity between the four lines persists in all observed features. In contrast, the Lyman lines show little correlation with the other lines. Their emission regions appear broader in the spectroheliograms than the underlying sunspot structure and must not necessarily possess a counterpart in lower layers. From the central intensity of L above the umbra an electron density of 4.3 × 10¹⁰ cm^-3 n _e ^* 2.3 × 10¹¹ cm^-3 at 20 000 K is estimated.Mitteilungen aus dem Kiepenheuer-Institut Nr. 186.Stockholm Observatorium, S-13300 Saltsjöbaden, Sweden.Laboratoire de Physique Stellaire et Planétaire, CNRS, P.O. Box 10, F-91370 Verrières-le-Buisson, France.     

Observable consequences of kinetic and thermal AGN feedback in elliptical galaxies and galaxy clusters

We have constructed an analytical model of active galactic nuclei (AGN) feedback and studied its implications for elliptical galaxies and galaxy clusters. The results show that momentum injection above a critical value will eject material from low-mass elliptical galaxies, and leads to an X-ray luminosity, L _X, that is  ∝σ⁸⁻¹⁰  , depending on the AGN fuelling mechanism, where σ is the velocity dispersion of the hot gas. This result agrees well with both observations and semi-analytic models. In more massive ellipticals and clusters, AGN outflows quickly become buoyancy dominated. This necessarily means that heating by a central cluster AGN redistributes the intracluster medium (ICM) such that the mass of hot gas, within the cooling radius, should be  ∝ L _X(< r _cool)/[ g ( r _cool)σ]  , where   g ( r _cool)  is the gravitational acceleration at the cooling radius. This prediction is confirmed using observations of seven clusters. The same mechanism also defines a critical ICM cooling time of  ∼0.5 Gyr  , which is in reasonable agreement with recent observations showing that star formation and AGN activity are triggered below a universal cooling time threshold.     

Computation of the RATAN-600 radio telescope power beam pattern with allowance for diffraction effects in the southern-sector-with-flat-reflector mode

We report the results of computation of the power beam pattern (PB) of the RATAN-600 radio telescope operating in the Southern-sector-with-flat-reflector (South+flat) mode throughout the entire operating frequency range of the radio telescope with the allowance for diffraction effects in the space between the secondary, primary, and flat mirrors. We also computed the gain-phase field distributions at the mirror surfaces when operating in the South+flat mode and in single-sector observations at the close to horizon elevations. The width of the power beam pattern in the vertical direction is shown to decrease and the maximum of the diagram to shift towards lower elevations with increasing wavelength. When the radio telescope is operated in the South+flat mode the above two changes in the power beam pattern begin to show up at shorter wavelengths compared to the case of single-sector operation. The shift of the power beam pattern maximum is shown to depend on the height at which the antenna is mounted. The power beam pattern was computed both for the case of a focused antenna and for the case of the off-focus primary emitter. We report the results of the computation of the PB performed in terms of the Fresnel diffraction and geometrical optics approximations, and also based on the available experimental data. The diagrams computed using this technique agree well with the measured power beams.     

Old, Low-Mass, Metal-Rich (SMR) Stars

The authors of this paper try to disentangle the many problems arisen from a new enlarged sample of nearby low-mass,metal-rich-stars. These stars have reliable absolute magnitudes, deduced from Hipparcos parallaxes, precise bolometric corrections, effective temperatures and metal abundances from high resolution detailed spectroscopic analyses. Their ages have been derived from a grid of isochrones calculated with up to date physics. The main goal of this paper is to determine the ages of the slightly evolved SMR stars. Among those with well determinated ages about 80% of them have intermediate ages of (2 to 5 Gyr), but only 20% have ages of 8 Gyr or more. Nevertheless, the existence of very old metal-rich stars is confirmed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Specifying the mesoscale numerical forecast of heavy showers

Actual surface fields of meteorological variables 1–3 hours before the heavy showers are analyzed in detail for the purpose of their specification with WRF-ARW model. The complex of hygrothermodynamic characteristics needed for this purpose is discovered. The detailed satellite, radar, and synoptic data are also considered.     

An optimization scheme of instrumental soil water storage determination

An optimization scheme is considered of the method of instrumental determination of soil moisture used within the Roshydromet system. The scheme enables to reduce the volume of instrumental operations by 2.5–3 times using the empirical statistical dependences between the water content in different layers of the soil profile. Efficiency of the filtration of outliers in the data sample is studied on the basis of the analysis of regression residuals when deriving the regression equations.