Ion-by-Ion DEM Determination: I. Method

We describe a technique to derive constraints on the differential emission measure (DEM) distribution, a measure of the temperature distribution, of collisionally ionized hot plasmas from their X-ray emission line spectra. This technique involves fitting spectra using a number of components, each of which is the entire X-ray line emission spectrum for a single ion. It is applicable to high-resolution X-ray spectra of any collisionally ionized plasma and particularly useful for spectra in which the emission lines are broadened and blended such as those of the winds of hot stars. This method does not require that any explicit assumptions about the form of the DEM distribution be made and is easily automated.Comment: This paper was split in two. This version is part I. Part II may be found at astro-ph/050343

Systematic search for high-energy gamma-ray emission from bow shocks of runaway stars

Context. It has been suggested that the bow shocks of runaway stars are sources of high-energy gamma rays (E > 100 MeV). Theoretical models predicting high-energy gamma-ray emission from these sources were followed by the first detection of non-thermal radio emission from the bow shock of BD+43^\deg 3654 and non-thermal X-ray emission from the bow shock of AE Aurigae. Aims. We perform the first systematic search for MeV and GeV emission from 27 bow shocks of runaway stars using data collected by the Large Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope (Fermi). Methods. We analysed 57 months of Fermi-LAT data at the positions of 27 bow shocks of runaway stars extracted from the Extensive stellar BOw Shock Survey catalogue (E-BOSS). A likelihood analysis was performed to search for gamma-ray emission that is not compatible with diffuse background or emission from neighbouring sources and that could be associated with the bow shocks. Results. None of the bow shock candidates is detected significantly in the Fermi-LAT energy range. We therefore present upper limits on the high-energy emission in the energy range from 100 MeV to 300 GeV for 27 bow shocks of runaway stars in four energy bands. For the three cases where models of the high-energy emission are published we compare our upper limits to the modelled spectra. Our limits exclude the model predictions for Zeta Ophiuchi by a factor $\approx$ 5.Comment: 5 pages, 5 figures, 1 table, accepted by A&

Dynamical Ne K Edge and Line Variations in the X-Ray Spectrum of the Ultra-compact Binary 4U 0614+091

We observed the ultra-compact binary candidate 4U 0614+091 for a total of 200 ksec with the high-energy transmission gratings onboard the \chandra X-ray Observatory. The source is found at various intensity levels with spectral variations present. X-ray luminosities vary between 2.0$\times10^{36}$ \ergsec and 3.5$\times10^{36}$ \ergsec. Continuum variations are present at all times and spectra can be well fit with a powerlaw component, a high kT blackbody component, and a broad line component near oxygen. The spectra require adjustments to the Ne K edge and in some occasions also to the Mg K edge. The Ne K edge appears variable in terms of optical depths and morphology. The edge reveals average blue- and red-shifted values implying Doppler velocities of the order of 3500 \kms. The data show that Ne K exhibits excess column densities of up to several 10$^{18}$ cm$^{-2}$. The variability proves that the excess is intrinsic to the source. The correponding disk velocities also imply an outer disk radius of the order of $< 10^9$ cm consistent with an ultra-compact binary nature. We also detect a prominent soft emission line complex near the \oviii L$\alpha$ position which appears extremely broad and relativistic effects from near the innermost disk have to be included. Gravitationally broadened line fits also provide nearly edge-on angles of inclination between 86 and 89$^{\circ}$. The emissions appear consistent with an ionized disk with ionization parameters of the order of 10$^4$ at radii of a few 10$^7$ cm. The line wavelengths with respect to \oviiia\ are found variably blue-shifted indicating more complex inner disk dynamics.Comment: 24 pages, 8 figures, submitted to the Astrophyscial Main Journa

Environmental variables, pesticide pollution and meiofaunal community structure in two contrasting temporarily open/closed false bay estuaries

Environmental variables (including natural and anthropogenic stressors) and meiobenthic communities were sampled in a ‘natural’ (Rooiels) and a ‘disturbed’ (Lourens) estuary in the Western Cape, South Africa, bimonthly for 20 months. A primary aim of the study was to assess if the meiobenthic community structure is driven by different variables when comparing ‘natural’ versus ‘disturbed’ system. Due to the much smaller catchment of the Rooiels Estuary, many environmental variables were significantly different (p<0.001) from the variables in the Lourens Estuary, e.g. salinity, temperature, pH, total suspended solids, nitrate and depth. No pesticide concentrations were expected in the Rooiels Estuary due to the absence of agricultural development in the catchment. However, chlorpyrifos (8.9 µg/kg), prothiofos (22.0 µg/kg) and cypermethrin concentrations (0.42 µg/kg) were detected frequently, with the highest concentrations recorded during the summer months. Principal response curve analysis showed that temporal variability between sampling dates explained 42% of the variance in environmental variables and pesticide concentrations and spatial variability between the 2 estuaries explained 58%. Variables contributing most to the differences were higher concentrations of endosulfan, p,p-DDE and nitrate concentrations in the Lourens Estuary and larger grain size and higher salinity at the bottom in the Rooiels Estuary. In general the meiofaunal community in the Rooiels Estuary showed a significantly higher number of taxa (p<0.001), a significantly higher Shannon Wiener Diversity Index (

Effectiveness of acidizing geothermal wells in the South German Molasse Basin

In Germany, many hydro-geothermal plants have been constructed in recent years, primarily in the region of Munich. As the host formation here mainly consists of carbonates, nearly all recently drilled wells have been acidized in order to improve the well yield. In this study, the effectiveness of these acid treatments is analyzed with respect to the amount of acid used and the number of acid treatments carried out per well. The results show that the first acid treatment has the largest effect, while subsequent acidizing improves the well only marginally. Data also indicate that continued acidizing can lead to degradation of the well. These findings may not only be important for geothermal installations in Germany but also for projects, for example, in Austria, France or China where geothermal energy is produced from carbonate formations as well

Growth of Oxide Compounds under Dynamic Atmosphere Composition

Commercially available gases contain residual impurities leading to a background oxygen partial pressure of typically several 10^{-6} bar, independent of temperature. This oxygen partial pressure is inappropriate for the growth of some single crystals where the desired oxidation state possesses a narrow stability field. Equilibrium thermodynamic calculations allow the determination of dynamic atmosphere compositions yielding such self adjusting and temperature dependent oxygen partial pressures, that crystals like ZnO, Ga2O3, or Fe{1-x}O can be grown from the melt.Comment: 4 pages, 3 figures, talk on CGCT-4 Sendai, May 21-24, 200

Correlations in a two--chain Hubbard model

Equal time spin--spin and pair field correlation functions are calculated for a two-chain Hubbard model using a density-matrix numerical renormalization group approach. At half-filling, the antiferromagnetic and pair field correlations both decay exponentially with the pair field having a much shorter correlation length. This is consistent with a gapped spin-liquid ground state. Below half--filling, the antiferromagnetic correlations become incommensurate and the spin gap persists. The pair field correlations appear to follow a power law decay which is similar to their non-interacting U=0 behavior.Comment: 9 pages and 5 postscript figures, RevTeX 3.0, UCI-CMTHE-94-01 (revised version