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  • 1. Cruzalebes, P.
    et al.
    Rabbia, Y.
    Jorissen, A.
    Spang, A.
    Sacuto, S.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, The Uppsala Astronomical Observatory.
    Pasquato, E.
    Chiavassa, A.
    Chesneau, O.
    Freville, P.
    SPIDAST: a new modular software to process spectrointerferometric measurements2013In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 432, no 2, p. 1658-1671Article in journal (Refereed)
    Abstract [en]

    Extracting stellar fundamental parameters from Spectrointerferometric (SPI) data requires reliable estimates of observables and with robust uncertainties (visibility, triple product, phase closure). A number of fine calibration procedures are necessary throughout the reduction process. Testing departures from centrosymmetry of brightness distributions is a useful complement. Developing a set of automatic routines called spidast (made available to the community) to reduce, calibrate and interpret raw data sets of instantaneous spectrointerferograms at the spectral channel level, we complement (and in some respects improve) the ones contained in the amdlib Data Reduction Software. Our new software spidast is designed to work in an automatic mode, free from subjective choices, while being versatile enough to suit various processing strategies. spidast performs the following automated operations: weighting of non-aberrant SPI data (visibility, triple product), fine spectral calibration (subpixel level), accurate and robust determinations of stellar diameters for calibrator sources (and their uncertainties as well), correction for the degradations of the interferometer response in visibility and triple product, calculation of the centrosymmetry parameter from the calibrated triple product, fit of parametric chromatic models on SPI observables, to extract model parameters. spidast is currently applied to the scientific study of 18 cool giant and supergiant stars, observed with the VLTI/AMBER facility at medium resolution in the K band. Because part of their calibrators have no diameter in the current catalogues, spidast provides new determinations of the angular diameters of all calibrators. Comparison of spidast final calibrated observables with amdlib determinations shows good agreement, under good and poor seeing conditions.

  • 2.
    Davidsson, Björn
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics, The Uppsala Astronomical Observatory.
    Thermophysical Modelling and Mechanical Stability of Cometary Nuclei2003Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Comets are the most primordial and least evolved bodies in the Solar System. As such, they are unique sources of information regarding the early history of the Solar System. However, little is known about cometary nuclei since they are very difficult to observe due to the obscuring coma. Indirect methods are therefore often used to extract knowledge about nucleus parameters such as size, shape, density, material strength, and rotational properties. For example, tidal and non-tidal splitting of cometary nuclei can provide important information about nuclear densities and material strengths, but only if the criteria for mechanical stability are well known. Masses and densities of cometary nuclei can also be obtained by studying orbital modifications due to non-gravitational forces, but only if the thermophysics of comets can be modelled accurately.

    A detailed investigation is made regarding the mechanical stability of small Solar System bodies. New expressions for the Roche distance are derived, as functions of the size, shape, density, material strength, rotational period, and spin axis orientation of a body. The critical rotational period for centrifugal breakup in free space is also considered, and the resulting formulae are applied to comets for which the size, shape and rotational period have been estimated observationally, in order to place constraints on their densities and material strengths.

    A new thermophysical model of cometary nuclei is developed, focusing on two rarely studied features - layer absorption of solar energy, and parallel modelling of the nucleus and innermost coma. Sophisticated modelling of radiative transfer processes and the kinetics of gas in thermodynamic non-equilibrium form the basis for this work. The new model is applied to Comet 19P/Borrelly, and its density is estimated by reproducing the non-gravitational changes of its orbit.

  • 3. de Val-Borro, M.
    et al.
    Edgar, R. G.
    Artymowicz, P.
    Ciecielag, P.
    Cresswell, P.
    D'Angelo, G.
    Delgado-Donate, E. J.
    Dirksen, G.
    Fromang, S.
    Gawryszczak, A.
    Klahr, H.
    Kley, W.
    Lyra, Wladimir
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, The Uppsala Astronomical Observatory.
    Masset, F.
    Mellema, G.
    Nelson, R. P.
    Paardekooper, S. -J
    Peplinski, A.
    Pierens, A.
    Plewa, T.
    Rice, K.
    Schaefer, C.
    Speith, R.
    A comparative study of disc-planet interaction2006In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 370, no 2, p. 529-558Article in journal (Refereed)
    Abstract [en]

    We perform numerical simulations of a disc-planet system using various grid-based and smoothed particle hydrodynamics (SPH) codes. The tests are run for a simple setup where Jupiter and Neptune mass planets on a circular orbit open a gap in a protoplanetary disc during a few hundred orbital periods. We compare the surface density contours, potential vorticity and smoothed radial profiles at several times. The disc mass and gravitational torque time evolution are analysed with high temporal resolution. There is overall consistency between the codes. The density profiles agree within about 5 per cent for the Eulerian simulations. The SPH results predict the correct shape of the gap although have less resolution in the low-density regions and weaker planetary wakes. The disc masses after 200 orbital periods agree within 10 per cent. The spread is larger in the tidal torques acting on the planet which agree within a factor of 2 at the end of the simulation. In the Neptune case, the dispersion in the torques is greater than for Jupiter, possibly owing to the contribution from the not completely cleared region close to the planet.

  • 4.
    Festin, Leif
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics, The Uppsala Astronomical Observatory.
    The faintest stars: A study of white, red and brown dwarfs1998Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    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. The surveyed volume corresponds to 464 pc3 in the solar neighbourhood and contains 21 M dwarfs and 7 white dwarfs. The derived M-dwarf luminosity function is consistent with previous findings, showing no substantial upturnbeyond Mv = 16. The white dwarf space density is consistent with a 20% fraction of the dynamical matter in the solar neighbourhood residing in white dwarfs. This is in line with the most recent independent results obtained with different methods, making the white dwarfs the best explanation to the Milky Way dark matter at present.

    The brown dwarfs were studied in the Pleiades open cluster. The distance and age of the Pleiades make the rapidly fading brown dwarfs still rather bright and easy to detect. 850 arcmin2 were covered in a deep RIJK survey. Nine new possible cluster members were discovered, four of which are below the brown dwarf limit. The faintest of these has an estimated mass of 0.040 M. and is thereby the lowest mass brown dwarf identified in the Pleiades cluster at present. The derived Pleiades substellar luminosity function is consistent with a mass function index between 0 and 1, making the brown dwarfs unlikely to contribute more than a few percent to the cluster mass, which is also consistent with recent dynamical results.

  • 5.
    García Pérez, Ana Elia
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics, The Uppsala Astronomical Observatory.
    On the Abundances of Li, Be and O in Metal-Poor Stars in the Galaxy2005Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Stellar atmospheres constitute excellent environments to study the chemical evolution of our Galaxy. The chemical composition of these atmospheres reflects the composition of the gas from where these stars were born. As the Galaxy evolves, the composition of the gas changes from being primordial (Big-Bang nucleosynthesis) to being enriched in heavy elements (stellar and interstellar nucleosynthesis). The abundances of fragile chemical elements can be affected by stellar mixing processes. Precise lithium, beryllium and oxygen abundance determinations in old stars are presented in this thesis. These determinations are based on the analysis of the observed spectra of a sample of thirteen metal-poor subgiant stars. According to stellar mixing theories, these stars are in a stellar evolutionary stage in which mixing by convection is expected. Abundances of fragile elements like lithium and beryllium are thus expected to be affected by such mixing processes. As a consequence of this, the abundances of these elements are discussed in a dilution context. Lithium and beryllium abundances are compared with the abundances of stars with similar characteristics but in a less evolved stellar phase so that mixing processes have not acted yet. As expected, our abundances seem to be depleted following reasonably well the standard predictions. Stellar abundances of oxygen should give an estimate of the oxygen contribution of core-collapse supernovae to the interstellar medium. However, there is poor agreement among the abundances determined from different atomic or molecular indicators in general. Abundances coming from three different indicators are compared in this thesis. The abundances determined from the O I infrared triplet lines at 777.1-5 nm give the poorest agreement among the three indicators. The abundances based on OH ultraviolet lines around 310 nm are lower for the subgiants in comparison with previous studies of main-sequence stars, becoming even lower than values based on the O I forbidden line at 630.03 nm. Still the most reliable indicator appears to be the O I forbidden line which suggests a plateau-like or only slowly increasing [O/Fe] towards lower [Fe/H]. In addition, the line formation of the Be II ultraviolet resonance lines at 313.0-1 nm, commonly used for abundance determinations purposes, is investigated under non-local thermodynamic equilibrium. We find that the common assumption of local thermodynamic equilibrium typically gives systematic errors of about 0.1 dex.

    List of papers
    1. Oxygen abundances in metal-poor subgiants as determined from [OI], OI and OH lines
    Open this publication in new window or tab >>Oxygen abundances in metal-poor subgiants as determined from [OI], OI and OH lines
    Show others...
    2006 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 451, no 2, p. 621-642Article in journal (Refereed) Published
    Abstract [en]

    The debate on the oxygen abundances of metal-poor stars has its origin in contradictory results obtained using different abundance indicators. To achieve a better understanding of the problem we have acquired high quality spectra with the Ultraviolet and Visual Echelle Spectrograph at VLT, with a signal-to-noise of the order of 100 in the near ultraviolet and 500 in the optical and near infrared wavelength range. Three different oxygen abundance indicators, OH ultraviolet lines around 310.0 nm, the [O I] line at 630.03 nm and the O I lines at 777.1-5 nm were observed in the spectra of 13 metal-poor subgiants with . Oxygen abundances were obtained from the analysis of these indicators which was carried out assuming local thermodynamic equilibrium and plane-parallel model atmospheres. Abundances derived from O I were corrected for departures from local thermodynamic equilibrium. Stellar parameters were computed using -vs.-color calibrations based on the infrared flux method and Balmer line profiles, Hipparcos parallaxes and lines. [O/Fe] values derived from the forbidden line at 630.03 nm are consistent with an oxygen/iron ratio that varies linearly with [Fe/H] as . Values based on the O I triplet are on average (s.d.) higher than the values based on the forbidden line while the agreement between OH ultraviolet lines and the forbidden line is much better with a mean difference of the order of (s.d.). In general, our results follow the same trend as previously published results with the exception of the ones based on OH ultraviolet lines. In that case our results lie below the values which gave rise to the oxygen abundance debate for metal-poor stars.

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:uu:diva-92684 (URN)10.1051/0004-6361:20053181 (DOI)
    Available from: 2005-02-24 Created: 2005-02-24 Last updated: 2017-12-14Bibliographically approved
    2. Li and Be depletion in metal-poor subgiants
    Open this publication in new window or tab >>Li and Be depletion in metal-poor subgiants
    2006 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 447, no 1, p. 299-310Article in journal (Refereed) Published
    Abstract [en]

    A sample of metal-poor subgiants has been observed with the UVES spectrograph at the Very Large Telescope and abundances of Li and Be have been determined. Typical signal-to-noise per spectral bin values for the co-added spectra are of the order of 500 for the line (670.78 nm) and 100 for the doublet lines (313.04 nm). The spectral analysis of the observations was carried out using the Uppsala suite of codes and MARCS (1D-LTE) model atmospheres with stellar parameters from photometry, parallaxes, isochrones and Fe II lines. Abundance estimates of the light elements were corrected for departures from local thermodynamic equilibrium in the line formation. Effective temperatures and Li abundances seem to be correlated and Be abundances correlate with [O/H]. Standard models predict Li and Be abundances approximately one order of magnitude lower than main-sequence values which is in general agreement with the observations. On average, our observed depletions seem to be 0.1 dex smaller and between 0.2 and 0.4 dex larger (depending on which reference is taken) than those predicted for Li and Be, respectively. This is not surprising since the initial Li abundance, as derived from main-sequence stars on the Spite plateau, may be systematically in error by 0.1 dex or more, and uncertainties in the spectrum normalisation and continuum drawing may affect our Be abundances systematically.

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:uu:diva-92685 (URN)10.1051/0004-6361:20053182 (DOI)
    Available from: 2005-02-24 Created: 2005-02-24 Last updated: 2017-12-14Bibliographically approved
    3. Departures from LTE in the formation of the BeII UV resonance lines in late type stars
    Open this publication in new window or tab >>Departures from LTE in the formation of the BeII UV resonance lines in late type stars
    In: Astronomy & AstrophysicsArticle in journal (Refereed) Submitted
    Identifiers
    urn:nbn:se:uu:diva-92686 (URN)
    Available from: 2005-02-24 Created: 2005-02-24Bibliographically approved
  • 6.
    García Pérez, Ana Elia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, The Uppsala Astronomical Observatory.
    Asplund, Martin
    Primas, Francesca
    Nissen, Poul Erik
    Gustafsson, Bengt
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, Theoretical Astrophysics.
    Oxygen abundances in metal-poor subgiants as determined from [OI], OI and OH lines2006In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 451, no 2, p. 621-642Article in journal (Refereed)
    Abstract [en]

    The debate on the oxygen abundances of metal-poor stars has its origin in contradictory results obtained using different abundance indicators. To achieve a better understanding of the problem we have acquired high quality spectra with the Ultraviolet and Visual Echelle Spectrograph at VLT, with a signal-to-noise of the order of 100 in the near ultraviolet and 500 in the optical and near infrared wavelength range. Three different oxygen abundance indicators, OH ultraviolet lines around 310.0 nm, the [O I] line at 630.03 nm and the O I lines at 777.1-5 nm were observed in the spectra of 13 metal-poor subgiants with . Oxygen abundances were obtained from the analysis of these indicators which was carried out assuming local thermodynamic equilibrium and plane-parallel model atmospheres. Abundances derived from O I were corrected for departures from local thermodynamic equilibrium. Stellar parameters were computed using -vs.-color calibrations based on the infrared flux method and Balmer line profiles, Hipparcos parallaxes and lines. [O/Fe] values derived from the forbidden line at 630.03 nm are consistent with an oxygen/iron ratio that varies linearly with [Fe/H] as . Values based on the O I triplet are on average (s.d.) higher than the values based on the forbidden line while the agreement between OH ultraviolet lines and the forbidden line is much better with a mean difference of the order of (s.d.). In general, our results follow the same trend as previously published results with the exception of the ones based on OH ultraviolet lines. In that case our results lie below the values which gave rise to the oxygen abundance debate for metal-poor stars.

  • 7.
    García Pérez, Ana Elia
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics, The Uppsala Astronomical Observatory.
    Kiselman, Dan
    Departures from LTE in the formation of the BeII UV resonance lines in late type starsIn: Astronomy & AstrophysicsArticle in journal (Refereed)
  • 8.
    García Pérez, Ana Elia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, The Uppsala Astronomical Observatory.
    Primas, Francesca
    Li and Be depletion in metal-poor subgiants2006In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 447, no 1, p. 299-310Article in journal (Refereed)
    Abstract [en]

    A sample of metal-poor subgiants has been observed with the UVES spectrograph at the Very Large Telescope and abundances of Li and Be have been determined. Typical signal-to-noise per spectral bin values for the co-added spectra are of the order of 500 for the line (670.78 nm) and 100 for the doublet lines (313.04 nm). The spectral analysis of the observations was carried out using the Uppsala suite of codes and MARCS (1D-LTE) model atmospheres with stellar parameters from photometry, parallaxes, isochrones and Fe II lines. Abundance estimates of the light elements were corrected for departures from local thermodynamic equilibrium in the line formation. Effective temperatures and Li abundances seem to be correlated and Be abundances correlate with [O/H]. Standard models predict Li and Be abundances approximately one order of magnitude lower than main-sequence values which is in general agreement with the observations. On average, our observed depletions seem to be 0.1 dex smaller and between 0.2 and 0.4 dex larger (depending on which reference is taken) than those predicted for Li and Be, respectively. This is not surprising since the initial Li abundance, as derived from main-sequence stars on the Spite plateau, may be systematically in error by 0.1 dex or more, and uncertainties in the spectrum normalisation and continuum drawing may affect our Be abundances systematically.

  • 9.
    Gunnarsson, M.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, The Uppsala Astronomical Observatory.
    Bockelee-Morvan, D.
    Biver, N.
    Crovisier, J.
    Rickman, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, The Uppsala Astronomical Observatory.
    Mapping the carbon monoxide coma of comet 29P/Schwassmann-Wachmann 12008In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 484, no 2, p. 537-546Article in journal (Refereed)
    Abstract [en]

    Context. CO is assumed to be the main driver behind the activity of comet 29P/Schwassmann-Wachmann 1, which resides in a near-circular orbit at 6 AU from the Sun. Several properties of the outgassing of CO can be deduced from its millimetre-wave emission. Earlier studies have indicated CO production from the nucleus as well as an extended source. Aims. We have sought to further investigate the nature of the CO production in comet 29P/Schwassmann-Wachmann 1, through the use of newly available instrumentation. Methods. We used the HERA receiver array on the 30-m IRAM telescope to map the 230 GHz CO(J = 2-1) line in the comet with an unprecedented sensitivity and spatial coverage, and a high spectral resolution (20 kHz, i.e., 25 m s(-1)). A 36-point map, 60 by 60 '', was obtained in June 2003, and a 25-point map, 96 by 96 '', in January 2004. Results. The CO emission line has a characteristic asymmetric profile. Our analysis is based on a coma model, where the outgassing pattern is derived from the shape of this line at the central position of the map. When comparing to the observations, both maps show a line intensity at offset positions that is 2-3 times stronger than the model prediction. Different explanations for this are evaluated, and it is found that for the global coma character, an extremely low gas temperature in the inner coma reproduces the observed radial profile. A cold inner coma depletes the population of the CO J = 2 rotational level in the region closest to the nucleus, making spectra observed at offset positions relatively stronger. From the global appearance of the maps, the coma was found to be largely axisymmetric, and the presence of a strong extended source of CO, as indicated from earlier observations using the SEST telescope, was not seen. When examining the maps in more detail, a possible exception to this was seen in an area similar to 30 '' south of the comet, where an excess in emission is present in both maps. Model fits to the spectra based on the cold inner coma that we find, with an intital kinetic temperature T(kin) = 4 K, give a measure of Q(CO), the CO production rate. Q(CO) was found to be (3.9 +/- 0.2) x 10(28) mol s(-1) in June 2003, and (3.7 +/- 0.2) x 10(28) mol s(-1) in January 2004. These values are a factor similar to 1.5 higher than that derived using only the information available from non-mapped data, and this adjustment applies also to previously published production rates.

  • 10.
    Gunnarsson, Marcus
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics, The Uppsala Astronomical Observatory.
    Gas Production in Distant Comets2002Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    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. At these distances, water sublimation is inefficient, and cometary activity is dominated by outgassing of carbon monoxide.

    An observing campaign is presented, where the millimeter-wave emission from CO in comet 29P/Schwassmann-Wachmann 1 has been studied in detail using the Swedish-ESO Submillimetre Telescope (SEST). Coma models have been used to analyse the spectra. The production of CO is found to have two separate sources, one releasing CO gas on the nuclear dayside, and one extended source, where CO is produced from coma material, proposed to be icy dust grains.

    Radio observations of many molecules in comet C/1995 O1 (Hale-Bopp) have been carried out in a long-term international effort using several radio telescopes. An overview of the results is presented, describing the evolution of the gas production as the comet passed through the inner Solar system. Spectra recorded using the SEST, primarily of CO, for heliocentric distances from 3 to 11 AU are analysed in detail, also using coma models.

    The concept of icy grains constituting the extended source discovered in comet 29P/Schwassmann-Wachmann 1 is examined by theoretical modelling of micrometre-sized ice/dust particles at 6 AU from the Sun. It is shown that that such grains can release their content of volatiles on timescales similar to that found for the extended source.

  • 11.
    Hidalgo-Gomez, Ana Maria
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, The Uppsala Astronomical Observatory.
    Olofsson, Kjell
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, The Uppsala Astronomical Observatory.
    The chemical content of a sample of dwarf irregular galaxies2002In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 389, no 3, p. 836-844Article in journal (Refereed)
    Abstract [en]

    We present abundances of neon, nitrogen and oxygen of some nearby dwarf irregular galaxies. The elemental abundances are retrieved from long-slit spectroscopy of H II regions in the objects. The abundances are found to be sub-solar in all cases. For the dwarf irregular galaxy DDO 190 the abundances reported in this work are the first ever published. One object, DDO 167, proved to have an oxygen abundance about similar to the one of I Zw 18, even though the uncertainties are high. A comparison of the chemical abundances between all the groups of gas-rich galaxies have been performed and the main conclusion is that the dwarf gas-rich galaxies are not distinguishable on the basis of their chemical content.

  • 12.
    Hidalgo-Gámez, Ana Maria
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics, The Uppsala Astronomical Observatory.
    A study of possible chemical inhomogeneities of dwarf irregular galaxies and the influence on the Z-L relationship1999Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    A study on the chemical abundances of dwarf irregular galaxies (dI's) is presented in this work. This type of galaxies have typically low metallicity. First of all, a definition of dI is proposed, in order to obtain a homogeneous group of targets.

    Due to the small size of the dI galaxies and the absence of strong dynamical processes a homogeneous chemical composition is normally assumed. The main argument is that the gas in the interstellar medium of the galaxies are probably not too much affected by internal dynamics and could therefore be well mixed. This hypothesis has been investigated. Optical spectra for various star-forming regions (HII regions) in five dI's have been obtained and analysed. For all the HII regions, the chemical abundances of the whole region have been determined. Spectra of four of these HII regions are of very high quality which allow an additional study of possible variations of the chemical abundances within the regions. It could be concluded that the existence of variations in the chemical abundances, especially at large scales, may depend on thephysical properties of the galaxy and its environment.

    Another important aspect to study is the behaviour of the dI galaxies in the metallicity-luminosity plane. A deep study of previous relationships for this kind of objects were performed as well as the possible sources of dispersion from this relationship. With the results on the chemical abundances of eight galaxies and the latest distance determinations a new, weak, relationship between the metallicity and the luminosity was derived. The influence of the environment and other physical properties of the galaxies have also been studied.

  • 13.
    Hultman, John
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics, The Uppsala Astronomical Observatory.
    Dissipative formation of galaxies in hierarchical cosmology1998Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    A description and detailed tests of a numerical code for simulations of galaxy formation is presented. The dynamics is followed with fully adaptive and Lagrangian Smooth Particle Hydrodynamics (SPH) combined with a gravitational tree method. The severe numerical problem of sub-resolution clustering is solved by merging of gas particles.

    The code is used for Hydrodynamical simulations of the formation of galaxies in the mass range 109 - 1013M. The effect of an ambient UV radiation field, and the effect of metal enrichment of halo gas due to star formation and stellar evolution, are investigated. The UV radiation field is found to strongly affect galaxies with circular velocities less than ≈ 50 km/s. The effect is, however, not large enough to reconcile hierarchical clustering models with observations.

    I present numerical simulations of galaxy formation in a CDM scenario, including star formation, using the SPH and tree method on scales ranging from 20 Mpc down to less than 1 kpc. The gas component is treated as a two-phase medium, governed by thermal instability and supernova feedback. For a certain degree of supernova evaporation, several general properties of elliptical galaxies are reproduced, like shapes, r1/4-profiles, half-light radii, slow rotation and anisotropic velocity dispersions. A Faber-Jackson -like relation is observed, being of the form M ~ Σ2.6.

    No disk shaped objects form. The elliptical objects form through a hierarchical, star-forming "inside-out" collapse. The SFR has a rapidly raising and later exponentially decaying behaviour in individual objects. The stellar contribution to the closure density is around one percent. The co-moving average SFR shows an increasing behaviour with redshift. Low mass objects are strongly suppressed. Generally, the more massive objects are in place at z ~ 0.5 - 2. Although many problems and questions still remain, the overall impression is that surprisingly many properties of ellipticals are reproduced.

  • 14.
    Kochukhov, Oleg
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, The Uppsala Astronomical Observatory.
    Magnetic and Chemical Structures in Stellar Atmospheres2003Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    We present an investigation of the magnetic field geometries and inhomogeneous distribution of chemical elements in the atmospheres of peculiar A and B stars. Our study combines high-quality spectroscopic and spectropolarimetric stellar observations with the development and application of novel techniques for theoretical interpretation of the shapes and variability of stellar line profiles. In particular, we extend the method of Doppler imaging to the analysis of spectra in the four Stokes parameters, making it possible to derive detailed and reliable stellar magnetic maps simultaneously with the imaging chemical inhomogeneities.

    The magnetic Doppler imaging is applied to study of magnetic topologies and distributions of chemical elements in the peculiar stars α2 CVn and 53 Cam. We found that the magnetic field geometry of 53 Cam is considerably more complex than a low-order multipolar topology, commonly assumed for magnetic A and B stars. Our Doppler imaging analysis also led to a discovery and study of spots of enhanced mercury abundance in the atmosphere of α And, a star where the presence of a global magnetic field is unlikely.

    The ESO 3.6-m telescope is used to collect unique, very high spectral- and time-resolution observations of rapidly oscillating peculiar A (roAp) stars and to reveal line profile variations due to stellar pulsations. We present a detailed characterization of the spectroscopic pulsational behaviour and demonstrate a remarkable diversity of pulsations in different spectral lines. The outstanding variability of the lines of rare-earth elements is used to study propagation of pulsation waves through the stellar atmospheres and identify pulsation modes. This analysis led to a discovery of a non-axisymmetric character of pulsations in roAp stars.

    Our study of chemical stratification in the atmosphere of the roAp star γ Equ provides a compelling evidence for significant variation of the chemical composition with depth. We find a combined effect of extreme chemical anomalies and a growth of pulsation amplitude in the outermost atmospheric layers to be the most likely origin of the high-amplitude pulsational variations of the lines of rare-earth elements.

    Observations of cool magnetic CP stars are obtained with the ESO Very Large Telescope and are used for empirical investigation of the anomalies in the atmospheric temperature structure. We show that the core-wing anomaly of the hydrogen Balmer lines observed in some cool CP stars can be attributed to a hot layer at an intermediate atmospheric depth.

    List of papers
    1. Doppler imaging of stellar magnetic fields: I. Techniques
    Open this publication in new window or tab >>Doppler imaging of stellar magnetic fields: I. Techniques
    2002 In: Astronomy & Astrophysics, ISSN 0004-6361, Vol. 381, no 2, p. 736-756Article in journal (Refereed) Published
    Identifiers
    urn:nbn:se:uu:diva-90271 (URN)
    Available from: 2003-04-23 Created: 2003-04-23Bibliographically approved
    2. LTE spectrum synthesis in magnetic stellar atmospheres.: The interagreement of three independent polarised radiative transfer codes
    Open this publication in new window or tab >>LTE spectrum synthesis in magnetic stellar atmospheres.: The interagreement of three independent polarised radiative transfer codes
    Show others...
    2001 In: Astronomy & Astrophysics, ISSN 0004-6361, Vol. 374, no 1, p. 265-279Article in journal (Refereed) Published
    Identifiers
    urn:nbn:se:uu:diva-90272 (URN)
    Available from: 2003-04-23 Created: 2003-04-23Bibliographically approved
    3. Doppler imaging of stellar magnetic fields: II. Numerical experiments
    Open this publication in new window or tab >>Doppler imaging of stellar magnetic fields: II. Numerical experiments
    2002 In: Astronomy & Astrophysics, ISSN 0004-6361, Vol. 388, no 3, p. 868-888Article in journal (Refereed) Published
    Identifiers
    urn:nbn:se:uu:diva-90273 (URN)
    Available from: 2003-04-23 Created: 2003-04-23Bibliographically approved
    4. Doppler imaging of stellar magnetic fields
    Open this publication in new window or tab >>Doppler imaging of stellar magnetic fields
    Show others...
    2002 In: Astronomy & Astrophysics, ISSN 0004-6361, Vol. 389, no 2, p. 420-438Article in journal (Refereed) Published
    Identifiers
    urn:nbn:se:uu:diva-90274 (URN)
    Available from: 2003-04-23 Created: 2003-04-23Bibliographically approved
    5. Magnetic Doppler imaging of 53 Cameliopardalis in all four Stokes parameters
    Open this publication in new window or tab >>Magnetic Doppler imaging of 53 Cameliopardalis in all four Stokes parameters
    Show others...
    2004 In: Astronomy & Astrophysics, Vol. 414, no 4, p. 613-632Article in journal (Refereed) Published
    Identifiers
    urn:nbn:se:uu:diva-90275 (URN)
    Available from: 2003-04-23 Created: 2003-04-23Bibliographically approved
    6. The variability of the HgII λ3984 line of the mercury-manganese star α Andromedae
    Open this publication in new window or tab >>The variability of the HgII λ3984 line of the mercury-manganese star α Andromedae
    2002 In: The Astrophysical Journal, ISSN 0004-637X, Vol. 575, no 1, p. 449-460Article in journal (Refereed) Published
    Identifiers
    urn:nbn:se:uu:diva-90276 (URN)
    Available from: 2003-04-23 Created: 2003-04-23Bibliographically approved
    7. Time-resolved spectroscopy of the roAp star γ Equ
    Open this publication in new window or tab >>Time-resolved spectroscopy of the roAp star γ Equ
    2001 In: Astronomy & Astrophysics, ISSN 0004-6361, Vol. 374, no 2, p. 615-628Article in journal (Refereed) Published
    Identifiers
    urn:nbn:se:uu:diva-90277 (URN)
    Available from: 2003-04-23 Created: 2003-04-23Bibliographically approved
    8. Pulsational and rotational line profile variations of the roAp stars α Cir and HR 3831
    Open this publication in new window or tab >>Pulsational and rotational line profile variations of the roAp stars α Cir and HR 3831
    2001 In: Astronomy & Astrophysics, ISSN 0004-6361, Vol. 377, no 2, p. L22-L25Article in journal (Refereed) Published
    Identifiers
    urn:nbn:se:uu:diva-90278 (URN)
    Available from: 2003-04-23 Created: 2003-04-23Bibliographically approved
    9. Abundance stratification and pulsations in the atmosphere of the roAp star γ Equulei
    Open this publication in new window or tab >>Abundance stratification and pulsations in the atmosphere of the roAp star γ Equulei
    Show others...
    2002 In: Astronomy & Astrophysics, ISSN 0004-6361, Vol. 384, no 2, p. 545-553Article in journal (Refereed) Published
    Identifiers
    urn:nbn:se:uu:diva-90279 (URN)
    Available from: 2003-04-23 Created: 2003-04-23Bibliographically approved
    10. Interpretation of the core-wing anomaly of Balmer line profiles of cool Ap stars
    Open this publication in new window or tab >>Interpretation of the core-wing anomaly of Balmer line profiles of cool Ap stars
    2002 In: The Astrophysical Journal, ISSN 0004-637X, Vol. 578, no 1, p. L75-L78Article in journal (Refereed) Published
    Identifiers
    urn:nbn:se:uu:diva-90280 (URN)
    Available from: 2003-04-23 Created: 2003-04-23Bibliographically approved
  • 15. Kuhlbrodt, Björn
    et al.
    Örndahl, Eva
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics, The Uppsala Astronomical Observatory.
    Wisotzki, Lutz
    Jahnke, Knud
    High-redshift quasar host galaxy analysis with adaptive optics: A statistical approach2005In: Astronomy and Astrophysics, ISSN 0004-6361, Vol. 439, p. 497-512Article in journal (Refereed)
  • 16. Kupka, F.
    et al.
    Piskunov, Nikolai
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, Observational Astronomy.
    Ryabchikova, T. A.
    Stempels, H. C.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, The Uppsala Astronomical Observatory.
    Weiss, W. W.
    VALD-2: Progress of the Vienna Atomic Line Data Base1999In: Astronomy and Astrophysics Supplement Series, ISSN 0365-0138, E-ISSN 1286-4846, Vol. 138, no 1, p. 119-133Article in journal (Refereed)
  • 17.
    Lagerros, Johan S. V.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics, The Uppsala Astronomical Observatory.
    Thermal physics of asteroids1998Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The thermal infrared and microwave emission from asteroids have many applications. Fundamental physical properties can be investigated, which have implications for the geophysical evolution of the asteroids, and the early history of the solar system.

    A new thermophysical model of asteroids is presented. A number of physical processes previously neglected in the Standard Thermal Model are now considered. The new model predicts the thermal emission of asteroids, from mid-infrared to microwave wavelengths. The irregular shapes of asteroids are modelled in detail, and the spin state of the asteroids is taken into account, whereby it is possible to calculate model thermal lightcurves. The heat conduction into the surface material in general lowers the mid-infrared flux from main-belt asteroids. The model is able to explain the observed "beaming" of the emission into the solar direction, under the assumption that it is caused by the small-scale surface roughness. Subsurface scattering processes are considered when calculating the directional- and wavelength-dependent emissivity.

    The model is applied to a large database of observations in the wavelength range of 7-2 000 µm. The purpose is to derive the thermophysical properties of ten asteroids, selected as calibration targets for the instruments on board the Infrared Space Observatory. The results indicate very rough and porous surfaces, with low levels of heat conduction. The emissivity variessignificantly with wavelength.

  • 18. Lykasov, Gennady
    et al.
    Olsson, Emma
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics, The Uppsala Astronomical Observatory.
    Pethick, Christopher
    Long-wavelength spin- and spin-isospin correlations in nucleon matterManuscript (Other academic)
  • 19.
    Olsson, Emma
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics, The Uppsala Astronomical Observatory.
    Many-body Problems in the Theory of Stellar Collapse and Neutron Stars2004Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    When modelling the collapse of massive stars leading to supernova explosions and the cooling of neutron stars, understanding the microphysical processes, such as the interaction of neutrinos within a dense medium are of vital importance. The interaction of neutrinos with nucleons (neutrons and protons) is altered by the presence of the medium, compared to the same process with free nucleons. Neutrino scattering and production processes may be characterized in terms of the excitations that are created or destroyed in the nuclear medium. One way to analyse the effects of the medium is by using Landau's theory of normal Fermi liquids. This theory gives simple relationships between physical quantities such as the spin susceptibility or the response to a weak interaction probe in terms of Landau parameters, that are measures of the interaction between quasiparticles. One problem when using Landau Fermi liquid theory for nucleon matter is that the interaction has a tensor component. The tensor interaction does not conserve the total spin and, as a consequence, there are generally contributions to long-wavelength response functions from states that have more than one quasiparticle-quasihole pair in the intermediate state. Such contributions cannot be calculated in terms of Landau parameters alone, since in the usual formulation of Landau theory, only singlepair excitations are considered. In this thesis three problems are addressed. First, we obtain bounds on the contributions from more than one quasiparticle-quasihole pair by using sum-rule arguments. Second, we derive expressions for static response functions allowing for the tensor components of the interaction. We analyse which the most important effects are on the static response of nucleon matter, and find that the major contributions comes from renormalization of coupling constants and transitions to states with more than one quasiparticle-quasihole pair. Third, we show how contributions to the dynamical response coming from states containing two quasiparticle-quasihole pairs may be evaluated in terms of Landau theory if one allows for the effect of collisions in the Landau kinetic equation. We consider the case of asymmetric nuclear matter, and our work goes beyond earlier works in that they contain the effects of collisions in addition to those of the mean field.

    List of papers
    1. Multipair contributions to the spin response of nuclear matter
    Open this publication in new window or tab >>Multipair contributions to the spin response of nuclear matter
    2002 In: Physical Review C, ISSN 0556-2813, Vol. 66, p. 065803-Article in journal (Refereed) Published
    Identifiers
    urn:nbn:se:uu:diva-92473 (URN)
    Available from: 2004-11-12 Created: 2004-11-12Bibliographically approved
    2. Static response of Fermi liquids with tensor interactions
    Open this publication in new window or tab >>Static response of Fermi liquids with tensor interactions
    2004 In: Physical Review C, ISSN 0556-2813, Vol. 70, p. 025804-Article in journal (Refereed) Published
    Identifiers
    urn:nbn:se:uu:diva-92474 (URN)
    Available from: 2004-11-12 Created: 2004-11-12Bibliographically approved
    3. Long-wavelength spin- and spin-isospin correlations in nucleon matter
    Open this publication in new window or tab >>Long-wavelength spin- and spin-isospin correlations in nucleon matter
    Manuscript (Other academic)
    Identifiers
    urn:nbn:se:uu:diva-92475 (URN)
    Available from: 2004-11-12 Created: 2004-11-12 Last updated: 2010-01-13Bibliographically approved
  • 20.
    Olsson, Emma
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics, The Uppsala Astronomical Observatory.
    Haensel, Pawel
    Pethick, Christopher
    Static response of Fermi liquids with tensor interactions2004In: Physical Review C, ISSN 0556-2813, Vol. 70, p. 025804-Article in journal (Refereed)
  • 21.
    Olsson, Emma
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics, The Uppsala Astronomical Observatory.
    Pethick, Christopher
    Multipair contributions to the spin response of nuclear matter2002In: Physical Review C, ISSN 0556-2813, Vol. 66, p. 065803-Article in journal (Refereed)
  • 22. Ryabchikova, T. A.
    et al.
    Piskunov, Nikolai
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, Observational Astronomy.
    Stempels, H. C.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, The Uppsala Astronomical Observatory.
    Kupka, F.
    Weiss, W. W.
    The Vienna Atomic Line Data Base - a status report1999In: Physica scripta. T, ISSN 0281-1847, Vol. T83, p. 162-173Article in journal (Refereed)
  • 23.
    Ryde, Nils
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics, The Uppsala Astronomical Observatory.
    Infrared spectroscopic investigations of stellar winds from red giants2000Doctoral thesis, comprehensive summary (Other academic)
  • 24. Silvester, J.
    et al.
    Wade, G. A.
    Kochukhov, Oleg
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, The Uppsala Astronomical Observatory.
    Landstreet, J. D.
    Bagnulo, S.
    Magnetic Doppler imaging of Ap stars2008In: CONTRIBUTIONS OF THE ASTRONOMICAL OBSERVATORY SKALNATE PLESO, ISSN 1335-1842, Vol. 38, no 2, p. 341-346Article in journal (Refereed)
    Abstract [en]

    Historically, the magnetic field geometries of the chemically peculiar Ap stars were modelled in the context of a simple dipole field. However, with the acquisition of increasingly sophisticated diagnostic data, it has become clear that the large-scale field topologies exhibit important departures from this simple model. Recently, new high-resolution circular and linear polarisation spectroscopy has even hinted at the presence of strong, small-scale field structures, which were completely unexpected based on earlier modelling. This project investigates the detailed structure of these strong fossil magnetic fields, in particular the large-scale field geometry, as well as small scale magnetic structures, by mapping the magnetic and chemical surface structure of a selected sample of Ap stars. These maps will be used to investigate the relationship between the local field vector and local surface chemistry, looking for the influence the field may have on the various chemical transport mechanisms (i.e., diffusion, convection and mass loss). This will lead to better constraints on the origin and evolution, as well as refining the magnetic field model for Ap stars. Mapping will be performed using high resolution and signal-to-noise ratio time-series of spectra in both circular and linear polarisation obtained using the new-generation ESPaDOnS (CFHT, Mauna Kea, Hawaii) and NARVAL spectropolarimeters (Pic du Midi Observatory). With these data we will perform tomographic inversion of Doppler-broadened Stokes IQUV Zeeman profiles of a large variety of spectral lines using the INVERS10 magnetic Doppler imaging code, simultaneously recovering the detailed surface maps of the vector magnetic field and chemical abundances.

  • 25.
    Skoglöv, Erik
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics, The Uppsala Astronomical Observatory.
    The Dynamical Spin Vector Evolution of the Asteroids2002Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The dynamical evolution of the spin axis direction due to gravitational and thermal factors is examined. It is found that the spin axis variations generally are regular and relatively small for the bodies in the asteroid main belt. There are also reasons to believe that this is the case for minor objects beyond the main belt. However, it is found that these regular variations are larger when the orbital inclination of the objects is increased. This effect may explain certain features in the spin vector distribution of the main belt asteroids, not possible to explain by collisional factors. The spin vector evolution of the asteroids in the inner solar system, including the Earth- and Mars-crossing objects, is often subjected to strong forces related to frequencies in the orbital evolution. The variations in the spin vector direction are then very large and often subjected to chaos. The larger frequency related obliquity zones of the Mars-crossers are usually regular while the zones of the Earth-Mars-crossers often are of a chaotic nature. The spin vector evolution of asteroids with comet-like orbits is often chaotic regardless of initial obliquity. For the inner solar system asteroids, it is often possible for an initial prograde spin to turn into a retrograde one, or vice versa, due to the frequency related phenomena. Though some spin vector directions seem to be more probable than other ones over time, there are no indications for an evolution towards a more prograde or a more retrograde spin vector distribution.

    The effects on the spin vector evolution from the thermal Yarkovsky force are examined for objects with radii larger than 50 m. This force will affect the orbital evolution and thus indirectly affect the spin vector evolution. However, it is found that the studied effects are minor as compared to the gravitationally related ones. This is true both for the diurnal and the seasonal variants of the Yarkovsky force.

  • 26. Soubiran, C.
    et al.
    Allende Prieto, C.
    Altmann, M.
    Bragaglia, A.
    Clementini, G.
    Frémat, Y.
    Heiter, Ulrike
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, The Uppsala Astronomical Observatory.
    Joliet, E.
    Pancino, E.
    Sartoretti, P.
    Smart, R.
    Thuillot, W.
    Ground-Based Observations for Gaia (GBOG)2008In: SF2A-2008: Proceedings of the Annual meeting of the French Society of Astronomy and Astrophysics / [ed] C. Charbonnel, F. Combes and R. Samadi, 2008, p. 0035-Conference paper (Refereed)
    Abstract [en]

    This contribution gives an overview of the ground-based observing efforts organized to collect the auxiliary data mandatory for the calibrations and tests of the Gaia data processing.

  • 27. Szutowicz, S.
    et al.
    Krolikowska, M.
    Rickman, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, The Uppsala Astronomical Observatory.
    Non-gravitational motion of the Jupiter-family comet 81P/Wild 2 II. The active regions on the surface2008In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 490, no 1, p. 393-402Article in journal (Refereed)
    Abstract [en]

    Aims. The non-gravitational perturbations in the orbital motion of comet 81P/Wild 2 are investigated using a two-source model of outgassing. Methods. In the process of orbit improvement the nucleus orientation and the location of two active regions are found from numerical fitting of the non-gravitational acceleration model to positional observations of the comet. Two different approaches to the lag angle of the outgassing behind the subsolar meridian are considered, assuming this angle to be either constant or varying with heliocentric distance. Results. The derived spin axis orientation (I similar to 60 degrees, phi similar to 155 degrees) as well as the location of two active regions, the northern (beta = 84 degrees) and the southern one (beta = -42 degrees), agree with determinations based on different observations by other authors. Orbital linkages of two and three successive apparitions of 81P/Wild 2 indicate an evolution of the change in the orbital period, possible time variations of the spin axis of the comet and an increase of the source areas during the last five revolutions. The non-gravitational perturbations were also used to constrain the sizes of the two active areas as well as the mass and bulk density (similar to 400 kg m(-3)) of the comet nucleus. The modeled two-source water production curve is compared with the activity data represented by the observed water production curve and the brightness curve.

  • 28.
    Thorén, Patrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, The Uppsala Astronomical Observatory.
    Dwarf and Subgiant Stars as Probes of Galactic Chemical and Dynamical Evolution2001Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Stellar chemical abundances provide astronomers with vital information about the production of chemical elements. Some stars preserve the composition of the environment in which they were born on their surfaces. By analysing the light from a star, the abundances of elements, its age and its path in space can be derived, and translated into the language of galactic history.

    The spallative history of boron in the early Galaxy was reinvestigated by observations of an ultraviolet spectral line in the old star HD 140283 with the Hubble Space Telescope. The line was barely detected and the upper limit abundance derived was lower than expected, which calls for further observations of this line in halo stars.

    Stars evolved into subgiants were observed with the ESO CAT, La Silla, and NOT, La Palma, to deduce their usefulness for galactic evolution studies. The high resolution spectroscopy study of the 26 objects showed that these stars are indeed useful for such studies. They are more luminous than dwarf stars and their ages can be accurately derived. They do not seem to have changed their surface abundances due to their evolution into giants. Subgiants can successfully be used to observationally reach regions further from the Earth, which can remove local biases that may appear when only observing nearby dwarf stars.

    A NLTE investigation of neutral Ca showed that cool metal rich dwarf stars did not deviate significantly from LTE, as had earlier been suggested. By an LTE analysis of a sample of 17 such dwarfs, using recent MARCS atmospheres, synthetic spectroscopy and modern atomic line data, cool metal rich dwarfs were shown not to deviate significantly from the expected abundance patterns in a number of elements. This increases the number of potential targets for studies of galactic chemical evolution in the metal rich regime since most stars are cool.

  • 29. VandenBerg, Don A.
    et al.
    Edvardsson, Bengt
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, The Uppsala Astronomical Observatory.
    Eriksson, Kjell
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, The Uppsala Astronomical Observatory.
    Gustafsson, Bengt
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, The Uppsala Astronomical Observatory.
    On the use of blanketed atmospheres as boundary conditions for stellar evolutionary models2008In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 675, no 1, p. 746-763Article in journal (Refereed)
    Abstract [en]

    Stellarmodels have been computed for stars having [Fe/H] = 0.0 (assuming both the Grevesse & Sauval and Asplund et al. heavy-element mixtures) and -2.0 to determine the effects on the predicted T-eff scale of using boundary conditions derived from the latest MARCS model atmospheres. The latter were fitted in a fully consistent way to the interior models at the photosphere and at tau = 100: the resultant evolutionary sequences on the H-R diagram were found to be nearly independent of the chosen fitting point. Tracks were also computed in which the pressure at T = T-eff was obtained by integrating the hydrostatic equation together with either the classical gray T(tau, T-eff) relation or that derived by Krishna Swamy from an empirical solar atmosphere. Due to the effects of differences in the solar-calibrated values of the mixing-length parameter, alpha(MLT), very similar tracks were obtained for the different treatments of the atmosphere, except at solar abundances, where the models based on the Krishna Swamy T(tau, T-eff) relationship predicted similar to 150 K hotter giant branches than the others, in good agreement with the inferred temperatures of giants in the open cluster M67 from recent (V - K) -T-eff relations. Tracks that used new "scaled solar, differentially corrected'' MARCS atmospheres were found to agree well with those that employed the Krishna Swamy T(tau, T-eff) relationship, independently of the assumed metal abundance. (Gray atmospheres are quite different from MARCS models.) Fits of isochrones for [Fe/H] = -2.0 to the CMD of the globular cluster M68, as well as the possibility that alpha(MLT) varies with stellar parameters, are also discussed.

  • 30.
    Örndahl, Eva
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics, The Uppsala Astronomical Observatory.
    Quasar host galaxies at intermediate and high redshifts2003Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Quasars form one of the most energetic phenomena in the universe, and can be traced out to very large redshifts. By studying the galaxies which host the active nuclei, important insights can be gained into the processes that trigger and maintain the quasar powerhouse. The evolution rate of the quasar population is furthermore similar to that of ordinary galaxies, which implies a connection between black hole accretion and star formation in the host galaxies. While the properties of quasar host galaxies at low redshift have become better constrained in recent years, less is known about hosts at earlier cosmic epochs. In addition, though radio-quiet quasars are by far more common than their radio-loud counterparts their host galaxies have not been studied to the same extent, in particular not at higher redshifts.

    An imaging campaign of a large sample of quasars at intermediate redshift (0.4 < z < 0.8) was carried out at optical wavelengths using the Nordic Optical Telescope, and is studied in this thesis together with two smaller samples. The joint material forms more than half of the total number of observed sources in this redshift interval and increases the number of resolved radio-quiet hosts at z>0.4 considerably. The morphology and mean magnitudes are found to be similar for radio-loud and radio-quiet host galaxies. Both types of host are shown to have optical colours as blue as those of present-day late-type spirals and starburst galaxies, which is likely the result of ongoing star formation.

    With increasing redshift, observations of host galaxies become more difficult. High spatial resolution can be achieved with adaptive optics, but the variation of the point spread function in the near-infrared wavelength band which is most suited for detection is large and rapid. A statistical approach to the problem of characterizing the point spread function has been developed, making use of simulated objects which are matched to the different atmospheric conditions. Bright, compact host galaxies showing signs of merging and interaction were detected in this way for three quasars at z~2.2, which were observed with the ESO 3.6 m telescope. The method is not restricted to host galaxy analysis but can be utilized in other applications as well, provided that the underlying extended source can be described by an analytical model.

    List of papers
    1. An optical imaging study of 0.4 < z < 0.8 quasar host galaxies: I. Observations and reduction
    Open this publication in new window or tab >>An optical imaging study of 0.4 < z < 0.8 quasar host galaxies: I. Observations and reduction
    2003 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, Vol. 404, p. 883-899Article in journal (Refereed) Published
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:uu:diva-90498 (URN)
    Available from: 2003-05-07 Created: 2003-05-07 Last updated: 2013-03-17
    2. An optical imaging study of 0.4 < z < 0.8 quasar host galaxies: II. Analysis and interpretation
    Open this publication in new window or tab >>An optical imaging study of 0.4 < z < 0.8 quasar host galaxies: II. Analysis and interpretation
    2005 In: Astronomy and Astrophysics, ISSN 0004-6361, Vol. 443, p. 61-78Article in journal (Refereed) Published
    Identifiers
    urn:nbn:se:uu:diva-90499 (URN)
    Available from: 2003-05-07 Created: 2003-05-07Bibliographically approved