Sökning: "Astronomi och astrofysik"

Visar resultat 1 - 5 av 308 avhandlingar innehållade orden Astronomi och astrofysik.

  1. 1. Regolith Properties of Mercury Derived from Observations and Modelling

    Författare :Johan Warell; Nick Thomas; Uppsala universitet; []
    Nyckelord :NATURAL SCIENCES; NATURVETENSKAP; NATURVETENSKAP; NATURAL SCIENCES; Astronomy; Mercury; Moon; imaging; photometry; spectroscopy; regolith; space weathering; light scattering; spectral modelling; Astronomi; Astronomy and astrophysics; Astronomi och astrofysik; astronomi; Astronomy;

    Sammanfattning : The properties of Mercury's regolith have been investigated at optical and near-infrared wavelengths with high-resolution imaging, photometric, and spectroscopic observations with the Swedish Vacuum Solar Telescope and the Nordic Optical Telescope. A new global optical map at a spatial resolution of 200 km shows that the well known (from Mariner 10) and poorly known hemispheres are indistinguishable with respect to the distribution, number density, and morphological parameters of bright albedo features. LÄS MER

  2. 2. Numerical simulations of type III planetary migration

    Författare :Adam Peplinski; Pawel Artymowicz; Garrelt Mellema; John Papaloizou; Stockholms universitet; []
    Nyckelord :NATURAL SCIENCES; NATURVETENSKAP; NATURVETENSKAP; NATURAL SCIENCES; planetary system formation; Astronomy and astrophysics; Astronomi och astrofysik; Astronomy; astronomi; accretion; accretion discs; hydrodynamics; methods: numerical; planets and satellites: formation; Astronomy; Astronomi;

    Sammanfattning : Planets are believed to form in primordial gas-dust discs surrounding newborn stars. An important breakthrough in our understanding of planetary formation was the discovery of extra-solar planets around sun-like stars, especially the frequent occurrence of giant planets on close orbits (hot Jupiters). LÄS MER

  3. 3. Optical Turbulence Characterization for Ground-Based Astronomy

    Författare :Susanna Hagelin; Anna Rutgersson; Elena Masciadri; Valentina Zitelli; Uppsala universitet; []
    Nyckelord :NATURAL SCIENCES; NATURVETENSKAP; NATURAL SCIENCES; NATURVETENSKAP; NATURVETENSKAP; NATURVETENSKAP; NATURAL SCIENCES; NATURAL SCIENCES; site testing; atmospheric effects; turbulence; optical turbulence; applied meteorology; mesoscale models; Meteorology; Meteorologi; Astronomy and astrophysics; Astronomi och astrofysik; Meteorologi; Meteorology;

    Sammanfattning : The optical turbulence, which creates perturbations of the wavefronts coming from the stars, is caused by small-scale fluctuations in the index of refraction of the atmosphere and is a problem for astronomers because it limits the maximum resolution of the ground-based telescopes. One way of identifying the best sites to build astronomical observatories, where the influence of the optical turbulence is as small as possible, is to use the standard meteorological parameters to get a first idea of the potential of a site. LÄS MER

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

    Författare :Leif Festin; Uppsala universitet; []
    Nyckelord :NATURAL SCIENCES; NATURVETENSKAP; 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

  5. 5. Gas Production in Distant Comets

    Författare :Marcus Gunnarsson; F Peter Schloerb; Uppsala universitet; []
    Nyckelord :NATURAL SCIENCES; NATURVETENSKAP; NATURVETENSKAP; NATURAL SCIENCES; Astronomy; Comets; Radio Astronomy; Molecular Spectroscopy; Coma Models; Astronomi; Astronomy and astrophysics; Astronomi och astrofysik; astronomi; Astronomy;

    Sammanfattning : Molecular spectroscopy at radio wavelengths is a tool well suited for studying the composition and outgassing kinematics of cometary comae. This is particularly true for distant comets, i.e. comets at heliocentric distances greater than a few AU, where the excitation of molecules is inefficient other than for rotational energy levels. LÄS MER