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 Msol.   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. / 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 Msun.   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.

The use of Type Ia supernovae (SNe Ia) as distance indicators is essential for studying the expansion history of the Universe and for exploring the nature of dark energy. However, a lack of understanding of the progenitor systems and the empirically derived colour-brightness corrections represent severe limitations for SNe Ia as cosmological probes. In this thesis, we study how dust along the line of sight towards SNe Ia affects the observed light over a wide range of wavelengths; from X-rays to infrared. Unless properly corrected for, the existence of intergalactic dust will introduce a redshift dependent magnitude offset to standard candle sources and bias the cosmological parameter estimates as derived from observations of SNe Ia. We model the optical extinction and X-ray scattering properties of intergalactic dust grains to constrain the intergalactic opacity using a combined analysis of observed quasar colours and measurements of the soft X-ray background. We place upper limits on the extinction AB(z = 1) &lt; 0.10 - 0.25 mag, and the dust density parameter Ωdust &lt; 10−5 − 10−4 (ρgrain/3 g cm−3), for models with RV &lt; 12 − ∞, respectively. Dust in the host galaxies, and dust that may reside in the circumstellar (CS) environment, have important implications for the observed colours of SNe Ia. Using the Hubble Space Telescope and several ground based telescopes, we measure the extinction law, from UV to NIR, for a sample of six nearby SNe Ia. The SNe span a range of E(B − V ) ≈ 0.1 − 1.4 mag and RV  ≈ 1.5 − 2.7, showing a diversity of dust extinction parameters. We present mid- and far-infrared (IR) observations for a number of SNe Ia, obtained with the Herschel Space Observatory and Spitzer Space Telescope, addressing CS dust as an explanation for “peculiar” extinction towards some SNe Ia. No excess IR emission is detected, limiting CS dust masses, Mdust &lt; 10−5 solar masses. In particular, the timely appearance of SN 2014J in M82 - the closest SN Ia in several decades - allows for detailed studies, across an unprecedented wavelength range, of its lightcurve and spectral evolution along with the host galaxy and CS environment. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 5: Manuscript. Paper 6: Manuscript.</p>

The Galactic disk is home of many billion stars, one of which isour Sun. The stellar population of which the Sun is a member residesin the vertically thin spiral structure of the disk. There is a seconddisk population, the so-called thick disk, that has somewhat dierentspatial, kinematic and chemical properties as compared to the thindisk. It may be systematically older than the thin disk (Bernkopf et al.2001), with a star-formation hiatus separating the two. Observationsof thick-disk subgiants allow us to probe the chemical properties ofthese stars. As the subgiant evolutionary phase is short, age-datingthese stars is also possible. Are they in fact systematically older thanthe oldest thin-disk stars? This project will take rst steps towardsanswering this question based on new target selections done on DataRelease 1 of the Gaia mission. / Vintergatans disk innehåller flera miljarder stjärnor, varav en är vår Sol. Den stjärnbefolkning som Solen är medlem i ligger i den vertikalt tunna spiralstrukturen på skivan (tunna disken). Det finns en andra diskpopulation, den så kallade tjocka disken, som har något annorlunda rumsliga, kinematiska och kemiska egenskaper jämfört med den tunna disken. Den kan vara äldren än tunna disken (Bernkopf et al. 2001), med en stjärnbildningsstopp som skiljer de två. Genom att observera subjättar som är en del av den tjocka disken blir det möjligt att analysera dessa stjärnors kemiska egenskaper. Eftersom subjätte grenen är en kort evolutionär fas, åldersbestämmelse är också möjlig för dessa stjärnor. Är de faktiskt systematiskt äldre än de äldsta tunna diskens stjärnor? Detta projekt kommer att ta de första stegen mot att svara på denna fråga baserat på nya målval som gjorts på Data Release 1 från Gaia-uppdraget.

Radial velocity measurements are critical in finding and confirming exoplanets. To confine the parameters of the planet we naturally want to minimise the errors on the measurement. However the observed measurement error is now on the same order as the precision of the instrument. This so called jitter is related to the stellar activity (Wright 2005), i.e. the magnetic field of the star. In this paper we investigate if we can discover any correlation between the radial velocity variation and the magnetic activity of the star using HARPSpol spectra for the two stars Epsilon Eridani and GJ674.

At the end of the lives of low- to intermediate mass stars they can be found on the asymptotic giant branch (AGB). The AGB phase ends when the entire circumstellar envelope (CSE) is blown away in a superwindphase, in the end creating a planetary nebula. It is unknown what shapes the CSE and the planetary nebula. Binarity is a favored theory. In order to test this theory the CSE around the star R Aquarii has been studied using the emission from different molecules observed with ALMA. R Aquarii is a nearby binary system and therefore easy to study. The system consists of a Mira variable on the AGB and a hot white dwarf. It was found that only in the emission from the 12CO J=3–2 transition were the CSE resolved enough for any structure to be seen. The morphology was irregular and no clear symmetry was seen. A spot in the same molecular line was detected at high velocities (v = -23 km/s) relative to the star at a projected distance of 7 arcsec south of R Aqr. Line profiles for 12CO and 13CO follow the same shape but differs in magnitude, indicating that they can be found in the same structure. A mass loss rate of 6.5·10-7 solar masses per year was calculated for R Aquarii using line intensities obtained from the line profile of 12CO. The morphology and kinematics of the CO CSE of R Aquarii are discussed within the limitations of the current data set. More observations with better resolution are needed to better understand the morphology of the CSE of R Aquarii and draw firm conclusions.

The presence of dark matter is inferred at scales ranging from rotations of galaxies to imprints in the CMB – the Big Bang after-glow. The nature of dark matter is, however, still unknown as no detection other than the gravitational one has been made. This thesis presents two analyses searching for a neutrino signal from dark matter annihilations in the Milky Way. The first analysis searched for an excess of νμ charged current events with directions from the central region of the dark matter halo and, was focused on low energy events, thus probing low dark matter particle masses. Approximately 319 days of data collected with the 79-string configuration of the IceCube detector was used in the analysis. Despite a large deficit in the number of observed events the data were found to be consistent with background and upper limits were set on &lt;σⱴ&gt;. At the time of the analysis these limits were the strongest set by a neutrino experiment below 100 GeV. The second analysis was performed on a data sample originally used in an unfolding analysis of the atmospheric and astrophysical neutrino spectra. The data consisted of contained cascade events above 1 TeV collected with the 79-string configuration and the completed detector in the 86-string configuration during two years of data-taking. The limits set by this analysis were more constraining by up to a factor of 10 compared to previous IceCube analyses, and the most competitive limits are set assuming a Burkert halo profile. These two analyses prompted the development of a signal subtraction likelihood method to address the problem of signal contamination in background estimates based on scrambled data. Additionally a study concerning future extensions of IceCube in the Gen2 project is presented. The cascade reconstruction performance was examined and compared for different proposed detector extensions.

Through the spectral synthesis model YGGDRASIL, developed by E. Zackris- son et al. 2011, luminosities for the chemically pristine population III galaxies are retrieved and compared to the capabilities of the upcoming infrared telescopes, in particluar the Wide Field InfraRed Survey Telescope (WFIRST). In order to push the very faint galaxies into the detectable regime of the telescope, magnification by gravitational lensing needs to be introduced. The probabilities for the nec- essary magnifications at different redshifts in combination with the depth of the telescope are translated into required minimum number densities and minimum formation rates for detecting one object per survey area. Both photometric and spectroscopic detections are investigated and compared to limits predicted by theory. Three different initial mass functions (IMF) for the stars that make up the galaxy are used, two that are top-heavy, i.e centers around stellar masses of 10 − 500M⊙, and one that resembles the IMF that are used for stars of younger generations, with its distribution peak at below one solar mass. The most optimistic results comes from the model that focusses on a galaxy of very heavy stars (with a total galaxy mass of 105 − 106M⊙), that yields minimum number densities for photometric detection at z &gt; 10 that are lower or comparable to what has been predicted by theory. When the calculations are concerned with spectroscopy, the minimum number densities goes up and very massive galaxies (107M⊙) are required to reach the predicted limits at z &gt; 10 and to enable detection by WFIRST. A comparison between the upcoming infrared telescopes; WFIRST, James Webb Space Telescope (JWST) and Euclid, are performed with WFIRST as the strongest candidate for photometry and JWST as the preferred instrument for spectroscopy, with a strong dependence on the survey area.

Magnetic fields are important for multiple physical processes in and around stars, for these reasons improving the understanding of how they are generated and maintained is of great value. In this work the magnetic field structure of the eclipsing binary UV Piscium is investigated. This is done by utilising the Zeeman-Doppler Imaging technique that reconstructs stellar magnetic maps by combining the information of how the magnetic field affects spectral lines with the rotational modulation of spectral lines. In order to improve the signal-to-noise ratio the least squares deconvolution technique was used to combine multiple spectral lines into an average line profile. The high resolution circular polarisation observations analysed in this work were taken by the ESPaDOnS spectograph at the Canada-France-Hawaii Telescope during August and September of 2016. We reconstructed detailed magnetic field maps and obtained the average magnetic field strengths of 137G for the primary and 88G for the secondary, which is not unusual values for stars of this type. The methods used are however likely to underestimate the magnetic field strengths. This is because the lack of linear polarisation profiles likely results in systematic underestimation of magnetic field strengths, especially meridional components. Another issue that became apparent in this work is that in eclipsing binaries, without linear polarisation observations, there is a degeneracy between the different hemispheres, resulting in further uncertainties in the determination of surface magnetic field geometry. We also found that there is indication of surface evolution on the time scale of months as some observations taken around fifty days earlier were could not be phased with the main data set.

The open cluster Messier 67 is known to have chemical composition, metallicity and age (~ 4 Gyr) close to the Sun. Therefore, it is advantageous for stellar physical studies and of stellar evolution, in particular for solar like stars within the cluster. This work considers three such stars, the formerly studied solar twin M67-1194 and two more recently suggested solar twins M67-1787 &amp; 2018. Most solar twins show a ratio of volatile to refractory elements that systematically depart from the Sun’s. Our targets do not follow this trend as closely. Their composition is closer to the Sun and they are, therefore, exquisite targets for studies of stellar evolution within the cluster. However, their solar likeness also provides studies regarding the origin and evolution of the Solar system. The stellar ages of the solar twins are established through a chemical clock [Y/Mg] and via stellar isochrones from BaSTI. The latter age assessment of the solar twins is supplemented with the analysis of two subgiant stars M67-1442 &amp; 1844. We approach the isochrone-based method using spectroscopically, astrometrically and photometrically derived parameters. The different ages of the stars and methods thus estimate the age of the cluster itself. The chemical ages of the stars suggest a cluster age of 4.56  ±0.44 Gyr and the isochrone-based estimates suggests a cluster age within the range 3.30-5.51 Gyr. Our results thus affirm and imply a near solar age of the cluster.

No description available.