The heating of the solar corona has been investigated during four of decades and several mechanisms able to produce heating have been proposed. It has until now not been possible to produce quantitative estimates that would establish any of these heating mechanism as the most important in the solar corona. In order to investigate which heating mechanism is the most important, a more detailed approach is needed. In this thesis, the heating problem is approached ”ab initio”, using well observed facts and including realistic physics in a 3D magneto-hydrodynamic simulation of a small part of the solar atmosphere. The ”engine” of the heating mechanism is the solar photospheric velocity field, that braids the magnetic field into a configuration where energy has to be dissipated. The initial magnetic field is taken from an observation of a typical magnetic active region scaled down to fit inside the computational domain. The driving velocity field is generated by an algorithm that reproduces the statistical and geometrical fingerprints of solar granulation. Using a standard model atmosphere as the thermal initial condition, the simulation goes through a short startup phase, where the initial thermal stratification is quickly forgotten, after which the simulation stabilizes in statistical equilibrium. In this state, the magnetic field is able to dissipate the same amount of energy as is estimated to be lost through radiation, which is the main energy loss mechanism in the solar corona. The simulation produces heating that is intermittent on the smallest resolved scales and hot loops similar to those observed through narrow band filters in the ultra violet. Other observed characteristics of the heating are reproduced, as well as a coronal temperature of roughly one million K. Because of the ab initio approach, the amount of heating produced in these simulations represents a lower limit to coronal heating and the conclusion is that such heating of the corona is unavoidable.

<p>The barred spiral galaxy M83 (NGC5236) has been observed in the ¹²CO <i>J</i>=1–0 and <i>J</i>=2–1 millimetre lines with the Swedish-ESO Submillimetre Telescope (SEST). The sizes of the CO maps are 100×100, and they cover the entire optical disk. The CO emission is strongly peaked toward the nucleus. The molecular spiral arms are clearly resolved and can be traced for about 360º. The total molecular gas mass is comparable to the total Hi mass, but H₂dominates in the optical disk.</p><p>Iso-velocity maps show the signature of an inclined, rotating disk, but also the effects of streaming motions along the spiral arms. The dynamical mass is determined and compared to the gas mass. The pattern speed is determined from the residual velocity pattern, and the locations of various resonances are discussed. The molecular gas velocity dispersion is determined, and a trend of decreasing dispersion with increasing galactocentric radius is found.</p><p>A total gas (H₂+Hi+He) mass surface density map is presented, and compared to the critical density for star formation of an isothermal gaseous disk. The star formation rate (SFR) in the disk is estimated using data from various star formation tracers. The different SFR estimates agree well when corrections for extinctions, based on the total gas mass map, are made. The radial SFR distribution shows features that can be associated with kinematic resonances. We also find an increased star formation efficiency in the spiral arms. Different Schmidt laws are fitted to the data. The star formation properties of the nuclear region, based on high angular resolution HST data, are also discussed.</p>

<p>The X-ray Multi-mirror Mission, XMM-Newton was launched by the European Space Agency, ESA, in 1999. XMM-Newton carries six cameras, including a silicon pn-junction Charge Coupled Device, or pn-CCD camera. This camera has six operating modes, spatially as well as time resolved. The main objective of this project is to refine the Burst mode energy correction in order to align the measured energy spectra observed in the Burst mode with the spectra taken in the Full Frame mode. An observation of the line-rich supernova remnant called Cassiopeia A is used to evaluate the line positions in each mode such that the energy correction function used for the alignment can be modified accordingly. The analysis further treats the application of the correction on a source with a continuous spectrum, the Crab nebula. Discussion shows how to reduce eventual residuals in the Crab spectrum by modifying the correction function while keeping the alignment of the Cas-A spectra. The final product is an update of the corresponding published calibration file.</p>

<p><p>Med utgångspunkt från den teoretiska bakgrunden, definitionen av svarta hål och deras generella egenskaper har jag studerat villkor för bildandet av svarta hål från döende singulära stjärnor. Supernovaprocessen beskrivs tillsammans med hur neutronstjärnor kan påverkas av destabiliserande mekanismer som t.ex. kaonkondensation. Olika observationer samt alternativa teorier läggs fram som argument och motargument. Utifrån detta underlag drar jag slutsatsen att svarta hål kan existera i fler varianter än vad som hittills antagits, främst i form av s.k. lågmassiva svarta hål på 1,5-1,8 M_sol.</p><p> </p><p>Vidare skildras möjligheten att producera mikroskopiska svarta hål i LHC-acceleratorn (Large Hadron Collider) i CERN, de kontroverser som omgärdar detta fenomen och de kunskaper som skulle kunna vinnas från kontrollerade observationer av sådana objekt. Den generella slutsatsen här är det ofrånkomliga mötet mellan partikelfysik och astrofysik för att få tillgång till de allra djupaste insikterna om det universum vi lever i.</p></p> / <p>Building on the theoretical background, definition of black holes and their general characteristics, I have studied some conditions for the formation of black holes from dying singular stars. The supernova process is described along with the influence on neutron stars by destabilising mechanism such as kaon condensation. Various observations as well as alternative theories are presented for argumentation. From this material I draw the conclusion that black holes can exist in more varieties than has been previously assumed, foremost in the shape of low-massive black holes with masses between 1.5 and 1.8 M_sun.</p><p> </p><p>Furthermore the possibility to produce microscopic black holes in the LHC accelerator (Large Hadron Collider) at CERN is portrayed, together with the controversies that currently surround this phenomenon and the knowledge that could be won from controlled observations of such objects. The general conclusion here is the unavoidable meeting between particle physics and astrophysics in order to access the deepest insights about the Universe we inhabit.</p>

<p>Ett av de mest notoriska dilemman i dagens kosmologi är den mörka materians natur och dess förekomst i universum. Mot bakgrund av detta har nya forskningsdiscipliner med rötterna i Einsteins relativitetsteori växt fram, bl.a. teorin om gravitationslinser som möjliggör en indirekt observationsmetod av ljussvaga kompakta objekt som annars skulle vara mycket svåra eller omöjliga att upptäcka på traditionella vis, såsom svarta hål.</p><p>Via en genomgång av grundteorin för gravitationslinser, några enkla teoretiska studier och en grundläggande felmarginalsanalys illustreras hur olika typer av kompakta objekt i Vintergatans omedelbara omgivning kan ge upphov till vissa karakteristiska linsfenomen. Detta sätts i relation till rådande teorier om den tidigaste stjärnbildningen och de massiva kompakta rester som denna generation av mycket massiva stjärnor bör ha efterlämnat – i synnerhet <em>intermediära svarta hål</em> med massor på 100-1000 M_sol som ännu kan finnas i dagens mörka galaxhalor. Sådana objekt kan komma att upptäckas i betydligt högre grad i framtiden med de observationstekniker som är under utveckling idag. </p> / <p>One of the most notorious dilemmas in cosmology today is the nature of dark matter and its distribution in the universe. Due to this, new research disciplines originating from Einstein’s theory of relativity have emerged, among them the theory of gravitational lensing which makes it possible to indirectly observe faint compact objects that would otherwise be very difficult or impossible to discover with traditional means, up to and including black holes.</p><p>Through a rundown of the basic theory of gravitational lensing, a couple of simple theoretical models and an elementary error analysis, it is illustrated how different types of compact objects in the immediate vicinity of the Milky Way can yield various characteristic lensing phenomena. This is put in relation to contemporary theories regarding the earliest star formation and the massive compact remnants this generation of very massive stars should have left behind – particularly <em>intermediate black holes</em> with masses of 100-1000 M_sun that may still be found in dark galactic halos of today. Such objects can contribute to future observations carried out with the observational technology being developed at present.</p>

<p>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.</p><p>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.</p><p>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.</p><p>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.</p>

<p>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.</p><p>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.</p>

Observations of gamma-rays have been made from celestial sources such as active galaxies, gamma-ray bursts and supernova remnants as well as the Galactic ridge. The study of gamma rays can provide information about production mechanisms and cosmic-ray acceleration. In the high-energy regime, one of the dominant mechanisms for gamma-ray production is the decay of neutral pions produced in interactions of ultra-relativistic cosmic-ray nuclei and interstellar matter. Presented here is a parametric model for calculations of inclusive cross sections and transverse momentum distributions for secondary particles - gamma rays, elecrons, positrons, electron neutrinos, electron antineutrinos, muon neutrinos and muon antineutrinos - produced in proton-proton interactions. This parametric model is derived on the proton-proton interaction model proposed by Kamae et al.; it includes the diffraction dissociation process, Feynman-scaling violation and the logarithmically rising inelastic proton-proton cross section. To improve fidelity to experimental data for lower energies, two baryon resonance excitation processes were added; one representing the Delta(1232) and the other multiple resonances with masses around 1600 MeV/c^2. The model predicts the power-law spectral index for all secondary particles to be about 0.05 lower in absolute value than that of the incident proton and their inclusive cross sections to be larger than those predicted by previous models based on the Feynman-scaling hypothesis. The applications of the presented model in astrophysics are plentiful. It has been implemented into the Galprop code to calculate the contribution due to pion decays in the Galactic plane. The model has also been used to estimate the cosmic-ray flux in the Large Magellanic Cloud based on HI, CO and gamma-ray observations. The transverse momentum distributions enable calculations when the proton distribution is anisotropic. It is shown that the gamma-ray spectrum and flux due to a pencil beam of protons varies drastically with viewing angle. A fanned proton jet with a Gaussian intensity profile impinging on surrounding material is given as a more realistic example. As the observer is moved off the jet axis, the peak of the spectrum is moved to lower energies. / QC 20100803

Supernovae are some of the most energetic phenomena in the Universe and they have throughout history fascinated people as they appeared as new stars in the sky. Supernova (SN) 1987A exploded in the nearby satellite galaxy, the Large Magellanic Cloud (LMC), at a distance of only 168,000 light years. The proximity of SN 1987A offers a unique opportunity to study the medium surrounding the supernova in great detail. Powered by the dynamical interaction of the ejecta with the inner circumstellar ring, SN 1987A is dramatically evolving at all wavelengths on time scales less than a year. This makes SN 1987A a great ``laboratory'' for studies of shock physics. Repeated observations of the ejecta-ring collision have been carried out using the UVES echelle spectrograph at VLT. This thesis covers seven epochs of high resolution spectra taken between October 1999 and November 2007. Three different emission line components are identified from the spectra. A narrow (~10 km/s) velocity component emerges from the unshocked ring. An intermediate (~250 km/s) component arises in the shocked ring, and a broad component extending to ~15,000 km/s comes from the reverse shock. Thanks to the high spectral resolution of UVES, it has been possible to separate the shocked from the unshocked ring emission. For the unshocked gas, ionization stages from neutral up to Ne V and Fe VII were found. The line fluxes of the low-ionization lines decline during the period of the observations. However, the fluxes of the [O III] and [Ne III] lines appear to increase and this is found to be consistent with the heating of the pre-shock gas by X-rays from the shock interactions. The line emission from the ejecta-ring collision increases rapidly as more gas is swept up by the shocks. This emission comes from ions with a range of ionization stages (e.g., Fe II-XIV). The low-ionization lines show an increase in their line widths which is consistent with that these lines originate from radiative shocks. The high-ionization line profiles (Fe X-XIV) initially show larger spectral widths, which indicates that at least a fraction of the emission comes from non-radiative shocks.

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.