The Solar Heavy-Element Abundances. I. Constraints from Stellar Interiors

The latest solar atmosphere models including non-LTE corrections and three-dimensional hydrodynamic convection simulations predict a significant reduction in the solar metal abundance. This leads to a serious conflict between helioseismic data and the predictions of solar interiors models. We demonstrate that the helioseismic constraints on the surface convection zone depth and helium abundance combined with stellar interiors models can be used to constrain chemical composition. A detailed examination of the errors in the theoretical models disfavors strongly (disagreeing at the 15 σ level with the seismic data) the proposed new low abundance, while the models constructed with the older and higher solar abundances are consistent (within 2 σ). We then use the sensitivity of the seismic properties to abundance changes to invert the problem and infer a seismic solar heavy-element abundance mix with two components: meteoritic abundances and the light metals CNONe. Seismic degeneracies between the best solutions for the elements arise for changes in the relative CNONe abundances and their effects are quantified. We obtain Fe/H = 7.50 ± 0.045 ± 0.003(CNNe) and O/H = 8.86 ± 0.041 ± 0.025(CNNe) on the logarithmic scale, where H = 12 for the relative CNNe mixtures in the Grevese & Sauval mixture; the second error term reflects the uncertainty in the overall abundance scale from errors in the C, N, and Ne abundances relative to oxygen. These are consistent within the errors with the previous standard solar mixture but in strong conflict with the low oxygen abundance inferred from the three-dimensional hydro models. Changes in the Ne abundance can mimic changes in oxygen for the purposes of scalar constraints. However, models constructed with low oxygen and high neon are inconsistent with the solar sound speed profile. Implications for the solar abundance scale are discussed

Atomic data from the Iron Project.XLIII. Transition probabilities for Fe V

An extensive set of dipole-allowed, intercombination, and forbidden transition probabilities for Fe V is presented. The Breit-Pauli R-matrix (BPRM) method is used to calculate 1.46 x 10^6 oscillator strengths for the allowed and intercombination E1 transitions among 3,865 fine-structure levels dominated by configuration complexes with n <= 10 and l <= 9. These data are complemented by an atomic structure configuration interaction (CI) calculation using the SUPERSTRUCTURE program for 362 relativistic quadrupole (E2) and magnetic dipole (M1) transitions among 65 low-lying levels dominated by the 3d^4 and 3d^ 4s configurations. Procedures have been developed for the identification of the large number of fine-structure levels and transitions obtained through the BPRM calculations. The target ion Fe VI is represented by an eigenfunction expansion of 19 fine-structure levels of 3d^3 and a set of correlation configurations. Fe V bound levels are obtained with angular and spin symmetries SL\pi and J\pi of the (e + Fe VI) system such that 2S+1 = 5,3,1, L <= 10, J <= 8 of even and odd parities. The completeness of the calculated dataset is verified in terms of all possible bound levels belonging to relevant LS terms and transitions in correspondence with the LS terms. The fine-structure averaged relativistic values are compared with previous Opacity Project LS coupling data and other works. The 362 forbidden transition probabilities considerably extend the available data for the E2 and M1 transtions, and are in good agreement with those computed by Garstang for the 3d^4 transitions.Comment: 19 pages, 1 figure. This paper marks the beginning of a large-scale effort of ab initio atomic calculations that should eventually lead to re-calculation of accurate iron opacities. Astron. Astrophys. Suppl. Ser. (in press

Resolution and accuracy of resonances in R-matrix cross sections

We investigate the effect of resonances in photoionization and recombination cross sections computed using the R-matrix method. Photoionization and recombination rates derived from high-resolution cross sections for oxygen ions are compared with earlier works with less resolution and accuracy, such as in the widely used Opacity Project data. We find significant differences in photoionization rates for O II metastable states, averaged over Planck functions corresponding to ionizing radiation fields, with respect to the intrinsic accuracy of the calculations and improved resolution. Furthermore, for highly charged ions other physical effects are also important. Recombination rate coefficients, averaged over a Maxwellian distribution, are extremely sensitive to the position and resolution of near-threshold resonances, and radiation damping, in (e + O VII) --> O VI + hnu. Surprisingly however, the effect on the monochromatic and the mean Rosseland and Planck bound-free opacities is relatively small, but may be potentially significant.Comment: 11 pages, 4 figures, Journal of Physics

Metallicity Mapping with gri Photometry: The Virgo Overdensity and the Halos of the Galaxy

We describe the methodology required for estimation of photometric estimates of metallicity based on the SDSS gri passbands, which can be used to probe the properties of main-sequence stars beyond ~ 10 kpc, complementing studies of nearby stars from more metallicity-sensitive color indices that involve the u passband. As a first application of this approach, we determine photometric metal abundance estimates for individual main-sequence stars in the Virgo Overdensity, which covers almost 1000 square degrees on the sky, based on a calibration of the metallicity sensitivity of stellar isochrones in the gri filter passbands using field stars with well-determined spectroscopic metal abundances. Despite the low precision of the method for individual stars, internal errors of in [Fe/H] ~ +/- 0.1 dex can be achieved for bulk stellar populations. The global metal abundance of the Virgo Overdensity determined in this way is = -2.0 +/- 0.1 (internal) +/- 0.5 (systematic), from photometric measurements of 0.7 million stars with heliocentric distances from ~ 10 kpc to ~ 20 kpc. A preliminary metallicity map, based on results for 2.9 million stars in the northern SDSS DR-7 footprint, exhibits a shift to lower metallicities as one proceeds from the inner- to the outer-halo population, consistent with recent interpretation of the kinematics of local samples of stars with spectroscopically available metallicity estimates and full space motions.Comment: 4 pages, 2 figures, to appear in IAU Symp. 26

Wet chemical polishing for industrial type PERC solar cells

Industrial PERC cell process flows typically apply the polishing of the rear side after texturing as well as the edge isolation after POCl3 diffusion. In this paper, we present a novel single step polishing process which we apply post double sided texturing and diffusion in order to remove the rear emitter and to reduce the rear surface roughness. One challenge is to minimize the etch back of the front side emitter during rear side polishing due to the reactive gas phase of the polishing process. By optimizing the polishing process, we are able to limit the increase of the emitter sheet resistance below 5 Ω/sq. However, the wet cleaning post polishing contributes an additional 20 Ω/sq emitter sheet resistance increase which is subject to further optimization. We compensate the emitter sheet resistance increase due to wet cleaning by applying a 45 Ω/sq POCl3 diffusion instead of a 60 Ω/sq diffusion. The resulting PERC solar cells with polished rear surface post texture and diffusion show conversion efficiencies up to 19.6% which is comparable to the reference PERC cells which apply a rear protection layer instead of a polishing process.German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety/0325296Heraeus Precious MetalsRenaSingulus TechnologiesSolar Worl

Electronic and physico-chemical properties of nanmetric boron delta-doped diamond structures

Heavily boron doped diamond epilayers with thicknesses ranging from 40 to less than 2 nm and buried between nominally undoped thicker layers have been grown in two different reactors. Two types of [100]-oriented single crystal diamond substrates were used after being characterized by X-ray white beam topography. The chemical composition and thickness of these so-called deltadoped structures have been studied by secondary ion mass spectrometry, transmission electron microscopy, and spectroscopic ellipsometry. Temperature-dependent Hall effect and four probe resistivity measurements have been performed on mesa-patterned Hall bars. The temperature dependence of the hole sheet carrier density and mobility has been investigated over a broad temperature range (6K<T<450 K). Depending on the sample, metallic or non-metallic behavior was observed. A hopping conduction mechanism with an anomalous hopping exponent was detected in the non-metallic samples. All metallic delta-doped layers exhibited the same mobility value, around 3.660.8 cm2/Vs, independently of the layer thickness and the substrate type. Comparison with previously published data and theoretical calculations showed that scattering by ionized impurities explained only partially this low common value. None of the delta-layers showed any sign of confinement-induced mobility enhancement, even for thicknesses lower than 2 nm.14 page

Galactic Globular and Open Clusters in the Sloan Digital Sky Survey. II. Test of Theoretical Stellar Isochrones

We perform an extensive test of theoretical stellar models for main-sequence stars in ugriz, using cluster fiducial sequences obtained in the previous paper of this series. We generate a set of isochrones using the Yale Rotating Evolutionary Code (YREC) with updated input physics, and derive magnitudes and colors in ugriz from MARCS model atmospheres. These models match cluster main sequences over a wide range of metallicity within the errors of the adopted cluster parameters. However, we find a large discrepancy of model colors at the lower main sequence (Teff < ~4500 K) for clusters at and above solar metallicity. We also reach similar conclusions using the theoretical isochrones of Girardi et al. and Dotter et al., but our new models are generally in better agreement with the data. Using our theoretical isochrones, we also derive main-sequence fitting distances and turn-off ages for five key globular clusters, and demonstrate the ability to derive these quantities from photometric data in the Sloan Digital Sky Survey. In particular, we exploit multiple color indices (g - r, g - i, and g - z) in the parameter estimation, which allows us to evaluate internal systematic errors. Our distance estimates, with an error of sigma(m - M) = 0.03-0.11 mag for individual clusters, are consistent with Hipparcos-based subdwarf fitting distances derived in the Johnson-Cousins or Stromgren photometric systems.Comment: 26 pages, 28 figures. Accepted for publication in ApJ. Version with high resolution figures available at http://spider.ipac.caltech.edu/~deokkeun/sdss_iso.pd

The Solar Heavy Element Abundances: II. Constraints from Stellar Atmospheres

Estimates of the bulk metal abundance of the Sun derived from the latest generation of model atmospheres are significantly lower than the earlier standard values. In Paper I we demonstrated that a low solar metallicity is inconsistent with helioseismology if the quoted errors in the atmospheres models (of order 0.05 dex) are correct. In this paper we undertake a critical analysis of the solar metallicity and its uncertainty from a model atmospheres perspective, focusing on CNO. We argue that the non-LTE corrections for abundances derived from atomic features are overestimated in the recent abundance studies, while systematic errors in the absolute abundances are underestimated. If we adopt the internal consistency between different indicators as a measure of goodness of fit, we obtain intermediate abundances [C/H] = 8.44 +/- 0.06, [N/H] = 7.96 +/- 0.10 and [O/H] = 8.75 +/- 0.08. The errors are too large to conclude that there is a solar abundance problem, and permit both the high and low scales. However, the center-to-limb continuum flux variations predicted in the simulations appear to be inconsistent with solar data, which would favor the traditional thermal structure and lead to high CNO abundances of (8.52, 7.96, 8.80) close to the seismic scale. We argue that further empirical tests of non-LTE corrections and the thermal structure are required for precise absolute abundances. The implications for beryllium depletion and possible sources of error in the numerical simulations are discussed.Comment: 36 pages, 4 figures, submitted Ap