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.     

Predicted interplanetary distribution of Lyman-σ intensity and polarization

Our current understanding of the spatial and temporal distribution of interplan etary neutral hydrogen is currently limited to a comparison of Lyman-σ photometric data with predictions of the solar backscattered radiation using theoretical models. In this paper, how the uncertainties in current model calculations could be reduced through the future use of polarization measurements made from interplanetary spacecraft is investigated. In particular, inquiry into how a mapping of the degree of linear polarization made from a spacecraft at various locations in the Solar System can improve knowledge of the interstellar wind parameters, number density, temperature, and velocity, is made. A polarization measurement can, in principle, be made with very high precision. In this regard, being a relative quantity, a polarization measurement can be made independent of instrumental calibration and long-term sensitivity degredation. Furthermore, the sky distribution of both intensity and polarization has been calculated using a variety of models for the neutral hydrogen. It is found that the polarization distribution over the sky is quite different from that of the intensity distribution. It is also showed that the maximum degree of polarization of the Laymam-σ line increases with heliocentric distance of the spacecraft, varying from 0 up to ～ 18% at 20 AU.     

Ultra-Deep Optical Spectroscopy with PMAS. Using the Nod-and-Shuffle Technique

PMAS, the Potsdam Multi-Aperture Spectrophotometer, is a new integral field spectrograph in the optical, which is optimized for good transmission and high image quality from 350 nm to 1 μm. We present our plan to implement a CCD charge-shuffle mode to allow for beam switching with a very high degree of sky subtraction accuracy for faint object 3-D spectroscopy. This revised version was published online in July 2006 with corrections to the Cover Date.     

Resonant Periodic Orbits of Trans-Neptunian Objects

We study two and three-dimensional resonant periodic orbits, usingthe model of the restricted three-body problem with the Sun andNeptune as primaries. The position and the stability character ofthe periodic orbits determine the structure of the phase space andthis will provide useful information on the stability and longterm evolution of trans-Neptunian objects. The circular planarmodel is used as the starting point. Families of periodic orbitsare computed at the exterior resonances 1/2, 2/3 and 3/4 withNeptune and these are used as a guide to select the energy levelsfor the computation of the Poincaré maps, so that all basicresonances are included in the study. Using the circular planarmodel as the basic model, we extend our study to more realisticmodels by considering an elliptic orbit of Neptune and introducingthe inclination of the orbit. Families of symmetric periodicorbits of the planar elliptic restricted three-body problem andthe three-dimensional problem are found. All these orbitsbifurcate from the families of periodic orbits of the planarcircular problem. The stability of all orbits is studied. Althoughthe resonant structure in the circular problem is similar for allresonances, the situation changes if the eccentricity of Neptuneor the inclination of the orbit is taken into account. All theseresults are combined to explain why in some resonances there aremany bodies and other resonances are empty.     

Coincident seismic reflection/refraction studies of the continental lithosphere: a global review

Summary. Vertical-incidence reflection profiling has identified several characteristic features of the continental Iithosphere including a generally transparent upper crust, a reflective lower crust, reflections from the crust-mantle boundary, and a commonly transparent upper mantle. The underlying physical causes of these characteristic features remain poorly understood. This review summarizes additional information brought to bear on the physical properties of these characteristic crustal structures through the use of coincident wide-angle refraction profiling.     

Fresnel modeling of hematite crystal surfaces and application to martian hematite spherules

The gray crystalline hematite at Meridiani Planum first discovered by the Mars Global Surveyor Thermal Emission Spectrometer (MGS-TES) instrument occurs as spherules that have been interpreted as concretions. Analysis of the TES and mini-TES spectra shows that no 390 cm⁻¹ feature is present in the characteristic martian hematite spectrum. Here, we incorporate the mid-IR optical constants of hematite into a simple Fresnel reflectance model to understand the effect of emission angle and crystal morphology on the presence or absence of the 390 cm⁻¹ feature in an IR hematite spectrum. Based on the results we offer two models for the internal structure of the martian hematite spherules.     

Decomposition of Hudson estuary macrophytes: Photosynthetic pigment transformations and decay constants

Plant pigment decay constants were determined for four macrophytes collected from the Hudson Estuary.Typha angustifolia andScirpus fluviatilis were used as representatives of emergent aquatic vegetation (EAV), andPotamogeton sp. andVallisneria americana were used to represent submerged aquatic vegetation (SAV). Litter bags were maintained in an environmental chamber in the dark for 104 d. The fastest rate of total mass loss was in the SAVV. americana and slowest in the EAVT. angustifolia. Changes in carotenoid and chloropigment concentration resulting from microbial and meiofaunal heterotrophy in each of the macrophytes were quantified using reverse-phase, high-performance liquid chromatography (RP-HPLC) techniques. Chlorophyllc and the carotenoid, fucoxanthin, provided useful biomarkers in determining the presence of epiphytic diatom growth, which only occurred on the SAV. The highest concentrations of phaeophorbidea, commonly used as an indication of metazoan grazing, were found in the SAVV. americana. Low concentrations of phaeophorbidea in the SAVPotamogeton sp. indicate inefficient use of this SAV by meiofaunal grazers. Lutein decayed slower than all other carotenoids in both EAV and SAV. Microcosm studies such as this are necessary to further understand the mechanisms and kinetics of photosynthetic pigment transformations in natural systems.     

Flare stars and solar bursts: High resolution in time and frequency

Coronal loops on the Sun and nearby stars are investigated using observations at 20 cm wavelength with high resolution in time and frequency. Observations of the dwarf M star AD Leonis with high time resolution using the Arecibo Observatory have resulted in the discovery of a quasi-periodic train of circularly polarized spikes with a mean periodicity of 32 ± 5 ms and a total duration of 150 ms. The individual spikes had rise times of 5 ms, leading to an upper limit to the linear size L 1.5 × 10⁸ cm for the spike emitter. This size is only 0.005 of the estimated radius of AD Leonis. Provided that the emitter is symmetric, it has a brightness temperature of T _B 10¹⁶ K, suggesting a coherent burst mechanism such as an electron-cyclotron maser. Coronal oscillations might modulate the maser output, producing the quasi-periodic spikes. Observations at closely spaced wavelengths, or high frequency resolution, using the Very Large Array have revealed narrow-band structure (v/v 0.01) in solar bursts and in the slowly-varying radiation of the dwarf M star YZ Canis Minoris. The narrow-band emission cannot be explained by continuum emission processes, but it might be attributed to electron-cyclotron maser radiation. Maser action at the second or first harmonic of the gyrofrequency implies magnetic field strengths of 250 and 500 G, respectively. Thus, observations with high resolution in time and frequency suggest coherent processes in the coronae of the Sun and dwarf M stars. The scientific potential of these discoveries may be best fulfilled by the construction of a solar-stellar synthesis radiotelescope.Proceedings of the Workshop on Radio Continua during Solar flares, held at Duino (Trieste), Italy, 27–31 May, 1985.     

Fluid and source magma evolution of the Questa porphyry Mo deposit,New Mexico,USA

Combined fluid inclusion microthermometry and microanalysis by laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) are used to constrain the hydrothermal processes forming a typical Climax-type porphyry Mo deposit. Molybdenum mineralisation at Questa occurred in two superimposed hydrothermal stages, a magmatic-hydrothermal breccia and later stockwork veining. In both stages, texturally earliest fluids were single-phase, of low salinity (~7 wt.% NaCl_equiv.) and intermediate-density. Upon decompression to ~300 bar, they boiled off a vapour phase, leaving behind a residual brine (up to 45 wt.% NaCl_equiv) at temperatures of ~420°C. The highest average Mo concentrations in this hot brine were ~500 μg/g, exceeding the Mo content of the intermediate-density input fluid by about an order of magnitude and reflecting pre-concentration of Mo by fluid phase separation prior to MoS₂ deposition from the brine. Molybdenum concentrations in brine inclusions, then, decrease down to 5 μg/g, recording Mo precipitation in response to cooling of the saline liquid to ~360°C. Molybdenite precipitation from a dense, residual and probably sulphide-depleted brine is proposed to explain the tabular shape of the ore body and the absence of Cu-Fe sulphides in contrast to the more common Cu-Mo deposits related to porphyry stocks. Cesium and Rb concentrations in the single-phase fluids of the breccia range from 2 to 8 and from 40 to 65 μg/g, respectively. In the stockwork veins, Cs and Rb concentrations are significantly higher (45–90 and 110–230 μg/g, respectively). Because Cs and Rb are incompatible and hydrothermally non-reactive elements, the systematic increase in their concentration requires two distinct pulses of fluid exsolution from a progressively more fractionated magma. By contrast, major element and ore metal concentrations of these two fluid pulses remain essentially constant. Mass balance calculations using fluid chemical data from LA-ICPMS suggest that at least 25 km³ of melt and 7 Gt of deep input fluid were necessary to provide the amount of Mo contained in the stockwork vein stage alone. While the absolute amounts of fluid and melt are uncertain, the well-constrained element ratios in the fluids together with empirical fluid/melt partition coefficients derived from the inclusion analyses suggest a high water content of the source melt of ~10%. In line with other circumstantial evidence, these results suggest that initial fluid exsolution may have occurred at a confining pressure exceeding 5 kbar. The source of the molybdenum-mineralising fluids probably was a particularly large magma chamber that crystallised and fractionated in the lower crust or at mid-crustal level, well below the shallow intrusions immediately underlying Questa and other porphyry molybdenum deposits. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.