نتایج جستجو برای: abundances

تعداد نتایج: 16306  

1997
Paolo Molaro

In this paper we review the present status of observations of the Big Bang elements D, 3He, 4He and 7Li and of their extrapolation to the primordial values. It is shown that, within the errors, the abundances are consistent with the predictions of the standard Big Bang nucleosynthesis for 1 ≤ η10 ≤ 6, which corresponds to 0.004 ≤ Ωbh 2 0 ≤ 0.02. Narrower consistencies in η10 are still possible ...

2008
Y. Zhang

We have determined fluorine abundances from the [F II] λ4789 and [F IV] λ4060 nebular emission lines for a sample of planetary nebulae (PNe). Our results show that fluorine is generally overabundant in PNe, thus providing new evidence for the synthesis of fluorine in asymptotic giant branch (AGB) stars. [F/O] is found to be positively correlated with the C/O abundance ratio, in agreement with t...

2005
Gary Steigman

The relic abundances of the light elements synthesized during the first few minutes of the evolution of the Universe provide unique probes of cosmology and the building blocks for stellar and galactic chemical evolution, while also enabling constraints on the baryon (nucleon) density and on models of particle physics beyond the standard model. Recent WMAP analyses of the CBR temperature fluctua...

2005
O. K. Manuel

The isotopic compositions of noble gases in the solar wind show high enrichments of light isotopes. When corrected for mass fractionation all five noble gases there can be resolved in terms of the two primitive noble gas components that have been identified in planetary solids. Reasons are presented for assigning the fractionation to a solar process that selectively enriches lighter nuclei at t...

2001
Max Pettini

It has recently become possible to measure directly the abundances of several chemical elements in a variety of environments at redshifts up to z 4. In this review I summarise the latest observations of Lyman break galaxies, the Lyman alpha forest and damped Lyman alpha systems with a view to uncovering any clues which these data may offer to the first episodes of star formation. The picture wh...

1997
Bengt Gustafsson

We have derived elemental abundances of O, Ni as well as for a number of s-elements for 47 G and K dwarf, with Me/H]> 0:1 dex. The selection of stars was based on their kinematics as well as on their uvby ?-photometry. One sample of stars on rather eccentric orbits traces the chemical evolution interior to the solar orbit and another, on circular orbits, the evolution around the solar orbit. A ...

2004
Sarbani Basu

Recent analyses of solar photospheric abundances suggest that the oxygen abundance in the solar atmosphere needs to be revised downwards. In this study we investigate the consequence of this revision on helioseismic analyses of the depth of the solar convection zone and the helium abundance in the solar envelope and find no significant effect. We also find that the revised abundances along with...

2000
I. Ilyin

High-resolution spectra of six core heliumburning ‘clump’ stars and three giants in the open cluster M 67 have been obtained with the SOFIN spectrograph on the Nordic Optical Telescope to investigate abundances of up to 25 chemical elements. Abundances of carbon were studied using the C2 Swan (0,1) band head at 5635.5 Å. The wavelength interval 7980–8130 Å with strong CN features was analysed i...

2002
James Di Francesco Michiel R. Hogerheijde William J. Welch Edwin A. Bergin

Abundances for 5 molecules (CO, CS, NH3, H2CO, and C3H2) and 1 molecular ion (N2H ) and upper limits for the abundances of 1 molecule (CO) and 1 molecular ion (HCO) are derived for gas within the Bok globule Barnard 68 (B68). The abundances were determined using our own BIMA millimeter interferometer data and single-dish data gathered from the literature, in conjunction with a Monte Carlo radia...

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