Sökning: "chemical abundances"

Visar resultat 21 - 25 av 51 avhandlingar innehållade orden chemical abundances.

  1. 21. Atomic Processes in Stellar Atmospheres : Inelastic Collisions and Effects on Late-type Spectra

    Författare :Yeisson Fabian Martinez Osorio; Paul Barklem; Karin Lind; Nikolai Piskunov; Carlos Allende Prieto; Uppsala universitet; []
    Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; NATURVETENSKAP; NATURAL SCIENCES; Spectral line: formation; atomic data; stellar abundances.; Fysik med inriktning mot astrofysik; Physics with specialization in Astrophysics;

    Sammanfattning : Chemical abundances as measured from stellar spectral lines are often subject to uncertainties due to lack of accurate data for inelastic collisions, which is needed for non-local thermodynamic equilibrium (non-LTE) modelling. For cool stars, understanding of collision processes with electrons and hydrogen atoms is required to achieve high precision measurements. LÄS MER

  3. 22. Modelling the Winds from Carbon Rich AGB Stars : Implications for Stellar Evolution and the Chemical Evolution of Galaxies

    Författare :Lars Mattsson; Uppsala universitet; []
    Nyckelord :;

    Sammanfattning : Stars on the AGB are known to lose mass at high rates (10-8 - 10-4 Msun/yr) through slow winds (20 km/s), enriching the inter stellar medium with newly synthesised elements. We explore how the mass loss for C-rich AGB stars depends on the basic stellar parameters by computing a large grid of wind models. LÄS MER

  4. 23. Solar Type Stars as Calibrators : A Photometric and Spectroscopic Study on the Atmospheric Properties of Late-type Stars

    Författare :Anna Önehag; Ulrike Heiter; Andreas Korn; Bengt Gustafsson; Frank Grundahl; Uppsala universitet; []
    Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; stars: atmospheres; stars: late-type; techniques: photometric; stars: abundances; techniques: spectroscopic; Astronomy; Astronomi;

    Sammanfattning : Detailed knowledge of solar-type stars is essential in the understanding of the evolutionary past, presence and future of the Sun as well as the formation of its planetary system. Moreover, solar-type stars are of key significance for the study of the evolution of the Galaxy. The ages of solar-type stars map the full galactic evolution. LÄS MER

  5. 24. Studies of Interstellar Molecular Gas in the Magellanic Clouds

    Författare :Arto Heikkilä; Chalmers tekniska högskola; []
    Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; abundances-Galaxies; evolution; molecules-Galaxies; Magellanic Clouds-Interstellar medium; molecules-Galaxies; interstellar medium-Galaxies;

    Sammanfattning : Results of observational studies of interstellar molecular gas clouds in the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC), two nearby metal-poor and dust-poor dwarf galaxies, are presented. Spectral line radiation emitted by interstellar molecules has been used to probe the physical state and the chemical composition of individual molecular clouds. LÄS MER

  7. 25. Modelling the middle atmosphere and its sensitivity to climate change

    Författare :Andreas Jonsson; Jörg Gumbel; Joanna Haigh; Stockholms universitet; []
    Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; climate change; middle atmosphere; ozone; carbon dioxide; stratosphere; mesosphere; chemical kinetics; atmospheric tides; Meteorology; Meteorologi;

    Sammanfattning : The Earth's middle atmosphere at about 10-100 km has shown a substantial sensitivity to human activities. First, the ozone layer has been reduced since the the early 1980s due to man-made emissions of halogenated hydrocarbons. LÄS MER