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High Metallicities (high + metallicity)

Distribution by Scientific Domains
Physics and Astronomy75%

Selected Abstracts

Single-Component Molecular Conductor [Pt(tmdt)2] (tmdt,=,trimethylenetetrathiafulvalenedithiolate) , An Advanced Molecular Metal Exhibiting High Metallicity

ADVANCED MATERIALS, Issue 35 2009
Biao Zhou
A newly prepared single-component molecular metal, [Pt(tmdt)2], exhibited very high conductivity and metallic behavior down to 4 K in the compacted polycrystalline state. A ,conducting paint' of [Pt(tmdt)2] obtained by kneading the microcrystals with lacquer and thinner showed metallic conductivity at around room temperature. [source]

Revisiting the origin of the high metallicities of sub-damped Lyman-alpha systems,

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2009
Miroslava Dessauges-Zavadsky
ABSTRACT Sub-damped Lyman-alpha systems (sub-DLAs) have previously been found to exhibit a steeper metallicity evolution than the classical damped Lyman-alpha systems (DLAs), evolving to close to solar metallicity by z, 1. From new high-resolution spectra of 17 sub-DLAs, we have increased the number of measurements of [Fe/H] at z < 1.7 by 25 per cent and compiled the most complete literature sample of sub-DLA and DLA abundances to date. We find that sub-DLAs are indeed significantly more metal-rich than DLAs, but only at z < 1.7; the metallicity distributions of sub-DLAs and DLAs at z > 1.7 are statistically consistent. We also present the first evidence that sub-DLAs follow a velocity width,metallicity correlation over the same velocity range as DLAs, but the relation is offset to higher metallicities than the DLA relation. On the basis of these results, we revisit the previous explanation that the systematically higher metallicities observed in sub-DLAs are indicative of higher host galaxy masses. We discuss the various problems that this interpretation encounters and conclude that in general sub-DLAs are not uniquely synonymous with massive galaxies. We rule out physically related sources of bias (dust, environment, ionization effects) and examine systematics associated with the selection and analysis of low-redshift sub-DLAs. We propose that the high metallicities of sub-DLAs at z < 1.7 that drives an apparently steep evolution may be due to the selection of most low-redshift sub-DLAs based on their high Mg ii equivalent widths. [source]

A comprehensive study of reported high-metallicity giant H ii regions , I. Detailed abundance analysis

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2002
Marcelo Castellanos
We present long-slit observations in the optical and near-infrared of 14 H ii regions in the spiral galaxies NGC 628, 925, 1232 and 1637, all of them reported to have solar or oversolar abundances according to empirical calibrations. For seven of the observed regions, ion-weighted temperatures from optical forbidden auroral to nebular line ratios are obtained and, for six of them, the oxygen abundances derived by standard methods turn out to be significantly lower than solar. The other one, named CDT1 in NGC 1232, shows an oxygen abundance of , and constitutes, to the best of our knowledge, the first high-metallicity H ii region for which accurate line temperatures, and hence elemental abundances, have been derived. For the rest of the regions no line temperature measurements could be made, and the metallicity has been determined by means of both detailed photoionization modelling and the sulphur abundance parameter S23. Only one of these regions shows values of O23 and S23 implying a solar or oversolar metallicity. According to our analysis, only two of the observed regions can therefore be considered as of high metallicity. These two fit the trends previously found in other high-metallicity H ii regions, i.e., N/O and S/O abundance ratios seem to be higher and lower than solar respectively. [source]