Wavelet Spectrum Analysis Of Eit/Soho Images

The extreme ultraviolet imaging telescope (EIT) of SOHO offers a unique record of the solar atmosphere for its sampling in temperature, field of view, resolution, duration, and cadence. To investigate globally and locally its topology and evolution during the solar cycle, we consider a multi-scale approach, and more precisely we use the wavelet spectrum. We present three results among the applications of such a procedure. First, we estimate the typical dimension of the supergranules as seen in the 30.4 nm passband, and we show that the evolution of the characteristic network scale is almost in phase with the solar cycle. Second, we build pertinent time series that give the evolution of the signal energy present in the corona at different scales. We propose a method that detects eruptions and post-flaring activity in EUV image sequences. Third, we introduce a new way to extract active regions in EIT images, with perspectives in, e.g., long-term irradiance analysis.     

Testing the circumstellar disc hypothesis: a search for H2 outflow signatures from massive young stellar objects with linearly distributed methanol masers

The results of a survey searching for outflows using near-infrared imaging are presented. Targets were chosen from a compiled list of massive young stellar objects associated with methanol masers in linear distributions. Presently, it is a widely held belief that these methanol masers are found in (and delineate) circumstellar accretion discs around massive stars. If this scenario is correct, one way to test the disc hypothesis is to search for outflows perpendicular to the methanol maser distributions. The main objective of the survey was to obtain wide-field near-infrared images of the sites of linearly distributed methanol masers using a narrow-band 2.12-μm filter. This filter is centred on the  H₂ v = 1–0 S(1)  line; a shock diagnostic that has been shown to successfully trace CO outflows from young stellar objects. 28 sources in total were imaged of which 18 sources display H₂ emission. Of these, only two sources showed emission found to be dominantly perpendicular to the methanol maser distribution. Surprisingly, the H₂ emission in these fields is not distributed randomly, but instead the majority of sources are found to have H₂ emission dominantly parallel to their distribution of methanol masers. These results seriously question the hypothesis that methanol masers exist in circumstellar discs. The possibility that linearly distributed methanol masers are instead directly associated with outflows is discussed.     

Does sediment grain size affect diatom grazing by harpacticoid copepods?

Estuarine soft sediments support a diverse group of eukaryotic and prokaryotic organisms though the role of the sediment per se for the functioning of these organisms remains largely unknown. The present study aimed to test the effect of sediment grain size on the grazing activities of harpacticoid copepods. In controlled experiments, two common intertidal harpacticoid species (Paramphiascella fulvofasciata and Nitokra spinipes) were each offered a mix of two benthic diatom species (Navicula phyllepta and Seminavis robusta) in different sedimentary conditions. Several microcosms were created using a variety of sediment types, including fine silt (<63 microm), coarser grained sands (125-250, 250-450, 100-300 microm), artificial 'sediments' of glass beads (250-500, 2000 microm) and even the absence of sediment was tested. The diatoms were enriched in the stable carbon (13)C to facilitate tracing in the harpacticoids. Both copepod species were able to graze on the diatoms with highest uptake when sediment was absent. In contrast, both harpacticoid species showed no uptake in silty conditions. In general, grazing was favoured when mean sediment grain size increased. The strong negative effect of fine grains on the grazer's efficiency can be explained by the resulting differences in the structure (and accessibility) of the diatom biofilm on the one hand and the mobility of the grazer on the other hand. In view of the subtle equilibrium between primary producers and grazers, these results might have important implications for the effect of siltation of tidal flats due to, e.g., human activities.     

Dissolution and depletion of ferromagnesian minerals from Holocene tephra layers in an acid bog,New Zealand,and implications for tephra correlation

This study examines the depletion of ferromagnesian silicate minerals from a sequence of thin, distal, mainly rhyolitic tephra layers of Holocene age preserved in an acid peat bog (Kopouatai), North Island, New Zealand. The rate of such depletion has been fast, as indicated by the complete loss of biotite from one tephra layer (Kaharoa Tephra), in which it is normally dominant, in only ca. 770 yr. Chemical dissolution is advocated as the likely cause for the depletion, with amphiboles and other mineral grains commonly showing etch pits, microcaves, and other characteristic surface solution features. Theoretical thermodynamic and kinetic models show a marked increase in the rate of dissolution of all ferromagnesian minerals under conditions of low pH (< 4), but that where silica concentrations in solution are high the relative proportions of minerals remaining are unaffected. However, where concentrations of dissolved silica are low, as in most bog environments, the relative proportions of ferromagnesian minerals are affected as well as absolute amounts being decreased. Amphiboles are depleted relative to pyroxenes, consistent with kinetic studies. The results show that the identification and correlation of tephras on the basis of relative abundances of ferromagnesian minerals alone may be unreliable, and emphasise the need to use multiple criteria in such studies.     

Abundances of [WC] central stars and their planetary nebulaee

We review elemental abundances derived for planetary nebula (PN) WCcentral stars and for their nebulae. Uncertainties in the abundances of[WC] stars are still too large to enable an abundance sequenceto be constructed. In particular it is not clear why the hotter [WCE]stars have C and O abundances which are systematically lower than those oftheir supposed precursors, the [WCL] stars. This abundance differencecould be real or it may be due to unaccounted-for systematic effects inthe analyses. Hydrogen might not be present in [WC] star winds asoriginallysuggested, since broad pedestals observed at the base of nebular lines canplausibly be attributed to high velocity nebular components. It isrecommended that stellar abundance analyses should be carried out withnon-LTE model codes, although recombination line analyses can provideuseful insights. In particular, C II dielectronic recombinationlines provide a unique means to determine electron temperatures in cool[WC] star winds. We then compare the abundances found for PNe which have [WC] central starswith those that do not. Numerous abundance analyses of PNe have beenpublished, but comparisons based on non-uniform samples and methods arelikely to lack reliability. Nebular C/H ratios, which might be expected todistinguish between PNe around H-poor and H-rich stars, are rather similarfor the two groups, with only a small tendency towards larger values fornebulae around H-deficient stars. Nebular abundances should be obtainedwith photoionization models using the best-fitting non-LTE modelatmosphere for the central star as the input. Heavy-metal line blanketingstill needs to be taken into consideration when modeling the central star,as its omission can significantly affect the ionizing fluxes as well asthe abundance determinations. We discuss the discrepancies between nebularabundances derived from collisionally excited lines and thosederived from optical recombination lines, a phenomenon that may havelinks with the presence of H-deficient central stars.     

WIMPs and solar evolution code

The Saclay solar evolution code is used to check the effect of WIMPs on solar evolution. In this paper we study the effects of various types of Cosmion-matter interactions, give constraints on the crosssections compatible with the measured neutrino rate of 2 SNU on chlorine, and relate these constraints to ongoing dark matter detection experiments.Unité associée au CNRS UA 280, F-75251 Paris Cedex 05, France.On leave from LPC, Collège de France.     

Fast Segmentation of Solar Extreme Ultraviolet Images

A segmentation scheme for identifying large-scale structures (coronal holes, active regions, etc.) in solar extreme ultraviolet images, is presented. Unlike standard approaches, both the image intensity and the relative contribution of different wavelengths are used. Spectral information is important for compensating luminosity changes. The approach is illustrated with images taken in the extreme ultraviolet by the EIT telescope onboard SOHO. This supervised segmentation scheme, which incorporates a Bayesian classifier, is computationally simple, and can easily be used to track in near-real time structures, such as coronal holes.     

The dynamical structure of dwarf elliptical galaxies

Deep imaging and long-slit spectroscopy was obtained for a sample of dwarf ellipticals in the Fornax cluster, NGC 5044 and NGC 5898 groups using the ESO VLT. The observational data extend out to typically 1.5–2 effective radii and indicate a kinematic dichotomy in the family of ellipticals. The observed stellar kinematics indicate a luminosity–velocity dispersion relation largely supporting Supernova-driven stellar mass loss scenarios for the formation of dwarf ellipticals. Stellar dynamical models favour dark matter halos with typical mass-to-light ratios in the range of 3 to 9 solar units. This revised version was published online in August 2006 with corrections to the Cover Date.     

Beam Mode Expansion of Corrugated Conical Horns with Phase Correcting Lens: Application to Radioastronomy Receivers

A classical radioastronomy receiver is fed with a corrugated horn and an independent lens, both placed in a cryostat to lower the noise temperature. The beam is focused and directed using a combination of elliptical and plane mirrors. This paper proposes modifying the initial feeding system by placing the lens onto the horn aperture, thereby allowing a size reduction of the horn and lens, and a simplification of their mechanical design. The profiled lens is shaped to correct the phase error on the horn aperture. A quasi-optical model of the horn-plus-lens system has been developed using a Beam Mode Expansion (BME). Results using both a hyperbolic-planar lens and a spherical-elliptical lens, as well as results obtained by using Geometrical Optics (GO) with a Kirchoff–Huygens integration to get the far-field pattern, have been compared with measurements. As a direct application, a full focusing system for the new 40-m radiotelescope at the “Centro Astronómico de Yebes” is presented for the 22, 30 and 45 GHz bands. This paper has developed a QO model for a corrugated conical horn with a phase-correcting lens. This revised version was published online in July 2006 with corrections to the Cover Date.