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Visar resultat 1 - 5 av 12 avhandlingar som matchar ovanstående sökkriterier.

  1. 1. The faintest stars : A study of white, red and brown dwarfs

    Författare :Leif Festin; Uppsala universitet; []
    Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; Astronomy; brown dwarfs; white dwarfs; M dwarf; low luminosity; luminosity function; mass function; Pleiades; Astronomi; Astronomy and astrophysics; Astronomi och astrofysik; astronomi; Astronomy;

    Sammanfattning : The local space density of the faintest stars, including M dwarfs, white dwarfs and brown dwarfs has been studied by two different methods.By using dark nebulae as opaque outer screens, the luminosity functions of M dwarfs and white dwarfs were studied as volume-limited and dynamically unbiassed foreground samples. LÄS MER

  3. 2. Observational Studies of the Chemical Evolution in the Galactic Thin and Thick Disks

    Författare :Thomas Bensby; Astronomi - Genomgår omorganisation; []
    Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; Astronomy; Astronomi; Fysicumarkivet A:2004:Bensby;

    Sammanfattning : The origin and evolution of the thin and thick disks in the Galaxy have been studied by means of detailed stellar abundances. High-resolution spectra of 102 F and G dwarf stars have been obtained with the spectrographs on the ESO 3.6-m and ESO 1. LÄS MER

  4. 3. Karaktäristiken hos strukturmarken på olika altitud i Abiskoområdet – en koppling till klimat och komplex systemteori

    Författare :Gunnar Scharin; Christer Jonasson; Johan Kling; Uppsala universitet; []
    Nyckelord :Abisko; patterned ground; permafrost; non-sorted circles; altitude; self-generation; Geovetenskap med inriktning mot miljöanalys; Earth Science with specialization in Environmental Analysis; Earth Science with specialization in Physical Geography; Geovetenskap med inriktning mot naturgeografi; Biology with specialization in Ecological Botany; Biologi med inriktning mot ekologisk botanik;

    Sammanfattning : Subarctic and alpine areas are sensitive to climatic change when they lie at the margin of permafrost occurrence. Patterned ground in such areas is generated from an interplay among different mechanisms such as temperature, hydrology, soil texture, snow cower and vegetation. LÄS MER

  5. 4. A Photometric Study of the Galactic Disks based on Strömgren Photometry

    Författare :Anna Arnadottir; Astronomi - Genomgår omorganisation; []
    Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; density parameters; formation.; metallicity distribution function; thin disk; metallicities. Galaxy - thick disk; colours; Photometry - Strömgren; luminosities; SDSS. Stars - classification;

    Sammanfattning : One of the key questions in todays galaxy research is the formation and evolution of disk galaxies such as the Milky Way. Using observations in the intermediate band Stromgren uvby filter system we have investigated how both density and metallicity varies within the Galactic disks in order to learn more about the Galaxy and its past. LÄS MER

  7. 5. Magnetic fields of cool stars from near-infrared spectropolarimetry

    Författare :Alexis Lavail; Oleg Kochukhov; Nikolai Piskunov; Gaitee Hussain; Jeff Valenti; Uppsala universitet; []
    Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; stars: magnetic field; stars: pre-main-sequence; stars: late-type; techniques: spectroscopic; techniques: polarimetric; Astronomy; Astronomi;

    Sammanfattning : Magnetic fields rule many physical processes in and around stars throughout their lifetime. All cool stars possess a magnetic field, likely generated by dynamo processes. In order to properly understand the evolution of cool stars, we need to understand their magnetism. LÄS MER