منابع مشابه
Non-LTE Spectral Analysis of Extremely Hot Post-AGB Stars: Constraints for Evolutionary Theory
Spectral analysis by means of Non-LTE model-atmosphere techniques has arrived at a high level of sophistication: fully line-blanketed model atmospheres which consider opacities of all elements from H to Ni allow the reliable determination of photospheric parameters of hot, compact stars. Such models provide a crucial test of stellar evolutionary theory: recent abundance determinations of trace ...
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In previous studies we have shown that the optical variability of quasars increases, on average, with redshift. We explained this dependance in terms of a hardening of the spectrum during bright phases, coupled with the increase of the rest-frame frequency for increasing red-shift. We re-analize now these correlations on the basis of new light curves of PG quasars, recently published by the Wis...
متن کاملNon-LTE analysis of neutral magnesium in cool stars
Calculations of the statistical equilibrium of magnesium in the solar photosphere have shown that NLTE populations hardly affect Mg line formation in the Sun. However, in metal-poor dwarfs and giants the influence of electron collisions is reduced, and the ultraviolet radiation field, enhanced due to reduced background line opacity, results in more pronounced NLTE effects. In the photosphere of...
متن کاملNon-LTE analysis of neutral magnesium in the solar atmosphere
We investigate the formation of neutral magnesium lines in the solar photosphere with an atomic model containing 83 levels plus the ground state of Mg ii connected via radiative and collisional interactions. Synthetic line flux and intensity profiles are compared with the solar spectrum to study the relevant physical processes and their influence on the level populations and line profiles. For ...
متن کاملMaximising spectral efficiency in LTE cells
The efficiency with which spectrum is used in wireless communications systems is becoming increasingly important as a result of the expected growth in traffic demand and the finite nature of usable spectrum. Spectral efficiency, defined as throughput divided by bandwidth, is a useful metric for evaluating the use of spectrum in wireless systems. In any given area the achievable spectrum efficie...
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ژورنال
عنوان ژورنال: International Astronomical Union Colloquium
سال: 1989
ISSN: 0252-9211
DOI: 10.1017/s0252921100099565