A core-collapse supernova (CCSN) is an astronomical explosion that indicates the death of a massive star. The iron core of the star collapses into either a neutron star or a black hole while the rest of the material is expelled at high velocities. Supernovae (SNe) are important for the chemical evolution of the Universe because a large fraction of the heavier elements such as oxygen, silicon, and iron are liberated by CCSN explosions. Another important role of SNe is that the ejected material seed the next generation of stars and planets. From observations, it is clear that a large fraction of all massive stars undergoes SN explosions, but describing how SNe explode has remained a challenge for many decades. The attached papers focus on comparing theoretical predictions with observations, primarily observations of SN 1987A. The compact remnant in SN 1987A has not yet been detected and we have investigated how a compact object can remain hidden in the ejecta (Paper I and II). Because of the high opacity of the metal-rich ejecta, the direct X-ray observations are not very constraining even for potentially favorable viewing angles. However, the combined observations still strongly constrain fallback accretion and put a limit on possible pulsar wind activity. The thermal surface emission from a neutron star is consistent with the observations if our line of sight is dust-obscured, and only marginally consistent otherwise. Future observations provide promising opportunities for detecting the compact object. We have also compared the most recent three-dimensional neutrino-driven SN models that are based on explosion simulations with early X-ray and gamma-ray observations of SN 1987A (Paper III). The models that are designed to match SN 1987A fit the data well, but not all tensions can be explained by choosing a suitable viewing angle. More generally, the asymmetries do not affect the early emission qualitatively and different progenitors of the same class result in similar early emission. We also find that the progenitor metallicity is important for the low-energy X-ray cuto↵. Current instruments should be able to detect this emission from SNe at distances of 3–10 Mpc, which correspond to distances slightly beyond the Local Group. / En kärnkollapssupernova (CCSN) är en astronomisk explosion som indikerar slutet av en massiv stjärnas liv. Stjärnans järnkärna kollapsar antingen till en neutronstjärna eller ett svart hål medan resten av materialet slungas iväg med höga hastigheter. Supernovor (SNe) är viktiga för Universums kemiska utveckling eftersom en stor andel av alla tyngre element såsom syre, kisel, och järn frigörs i CCSN-explosioner. Ytterligare en viktig roll för SNe är att nästa generations stjärnor och planeter bildas av det utkastade materialet. Från observationer är det tydligt att en stor andel av alla massiva stjärnor genomgår SN-explosioner, men att förklara hur SNe exploderar har kvarstått som en utmaning under flera decennier. De bifogade artiklarna fokuserar på att jämföra teoretiska förutsägelser med observationer, primärt observationer av SN 1987A. Det kompakta objektet i SN 1987A har ännu inte blivit detekterat och vi har undersökt hur ett kompakt objekt kan förbli dolt i ejektat (Paper I och II). De direkta röntgenobservationerna är inte så begränsande även längs potentiellt gynsamma siktlinjer på grund av det metallrika ejektats höga opacitet. Däremot begränsar kombinationen av alla observationer starkt ackretion och sätter en gräns för möjlig pulsarvindsaktivitet. Den termiska ytstrålningen från en neutronstjärna är konsistent med observationerna om vår siktlinje är skymd av stoft, och bara marginellt konsistent annars. Framtida observationer utgör lovande möjligheter för att detektera det kompakta objektet. Vi har också jämfört de senaste tredimensionella neutrinodrivna SN-modellerna, som är baserade på explosionssimuleringar, med tidiga röntgen- och gamma-observationer av SN 1987A (Paper III). SN 1987A-modellerna passar datan väl, men alla diskrepanser kan inte förklaras av ett lämpligt val av observationsvinkel. Generellt så påverkar inte asymmetrierna den tidiga emissionen kvalitativt och olika föregångarstjärnor av samma kategori resulterar i likartad strålning. Vi finner också att föregångarstjärnans metallisitet är viktig för egenskaperna av lågenergiröntgenstrålningen. Befintliga instrument borde kunna detektera denna emission på 3--10 Mpc, vilket motsvarar avstånd lite bortom den Lokala galaxhopen. / <p>Examintor: Professor Mark PearceQC 20190121</p>

Recent detections of massive quasars at z &gt; 6 has proven to be an interesting challengefor cosmology given the short time frame that these objects have to reach a certainmass via conventional methods (e.g., galaxy mergers). Direct collapse black holes(DCBHs) are theorized black hole seeds that propose a neat solution to the formationof supermassive black holes (SMBHs) by z ≳ 6. During this report, we followed thefirst photometric method developed to identify these black hole seeds, adapting it tothe James Webb Space Telescope (JWST ) photometric system to facilitate its usefor upcoming data. Two DCBH models were used to discard nearby objects (e.g.,cool stars, brown dwarfs and giant exoplanets) as possible interlopers, and allowed usto identify a possible confusion between DCBH signatures and high-redshift galaxies(z = 6) within an age range of 0.8-0.9 Gyr. This confusion could grow larger if wereconsider the analysis adding dust to the galaxy models we used

The aim of this master thesis is to investigate the influence of intergalactic duston astronomical observations. The current cosmological paradigm of an acceleratingcosmic expansion is supported by observations of Type Ia supernovae. However, thelight emitted by these and other cosmological sources is not only redshifted by cosmicexpansion but will also interact with matter along the light path which affects the light.Especially intergalactic dust can lead to additional reddening and dimming of distantsources due to light scattering or absorption. This yields systematic contaminations tocosmological measurements. Using quasars as backlight sources we seek to estimate theattenuation of their observed spectra caused by intergalactic dust in order to determinethe existence and properties of the intergalactic dust. In this thesis we will analysethe methods and tools used as well as discussing the dust properties and how theyaffect the results. This thesis shows that intergalactic dust exist, and has a notableeffect on cosmological measurements and favors dust grains consisting of silicate witha size around 0.1 µm with Ωdust around 5 − 7 × 10^−6. The conclusion is in agreementwith previous studies of the same matter. With the increasing precision of cosmologicalmeasurements systematic effects such as intergalactic dust is a factor that has to betaken into account. / Syftet med denna masteruppsats är att undersöka de effekter intergalaktiskt stofthar på astronomiska observationer. Den ledande kosmologiska moddellen som säger attuniversum expanderar är stöttad av observationer av Typ 1a supernovor. Ljuset somkommer från supernovorna är däremot inte bara påverkade av den kosmiska expansionen men kommer också interagera med materia på vägen som påverkar ljuset. Specielltintergalaktiskt stoft kan leda till ytterligare dimning av ljuset och att ljuset blir rödare.Detta är på grund av spridningen eller absorptionen av ljuset när ljuset interagerar medstoftpartiklarna. Detta leder till systematiska fel i kosmologiska mätningar. Genomatt använda kvasarer som en ljuskälla försöker vi uppskatta ljusdämpningen på derasspektrum som orsakats av intergalaktiskt stoft. Detta görs för att bestämma ifall intergalaktiskt stoft existerar och vad dess egenskaper är. I denna uppsats gjordes enanalys av metoden, beräkningsverktygen som användes och några egenskaper hos stoft.Slutsatsen av denna analys visar på att intergalaktiskt stoft existerar och har en mätbar effekt på kosmologiska observationer. Resultatet visar att modellen föredrar stoftav silikat med storlekar runt 0.1 µm med Ωdust runt 5 − 7 × 10^−6vilket stämmer överens med tidigare studier. Med den ökade pressionen av kosmologiska mätningar blirsystematiska effekter, som den från intergalaktiskt stoft, ännu viktigare att ta i hänsyn.

<p>Type Ia supernovae can be used as distance indicators for probing the expansion history of the Universe. The method has proved to be an efficient tool in cosmology and played a decisive role in the discovery of a yet unknown energy form, dark energy, that drives the accelerated expansion of the Universe. The work in this thesis addresses the nature of dark energy, both by presenting existing data, and by predicting opportunities and difficulties related to possible future data.</p><p>Optical and infrared measurements of type Ia supernovae for different epochs in the cosmic expansion history are presented along with a discussion of the systematic errors. The data have been obtained with several instruments, and an optimal method for measuring the lightcurve of a background contaminated source has been used. The procedure was also tested by applying it on simulated images.</p><p>The future of supernova cosmology, and the target precision of cosmological parameters for the proposed SNAP satellite are discussed. In particular, the limits that can be set on various dark energy scenarios are investigated. The possibility of distinguishing between different inverse power-law quintessence models is also studied. The predictions are based on calculations made with the Supernova Observation Calculator, a software package, introduced in the thesis, for simulating the light propagation from distant objects. This tool has also been used for investigating how SNAP observations could be biased by gravitational lensing, and to what extent this would affect cosmology fitting. An alternative approach for estimating cosmological parameters, where lensing effects are taken into account, is also suggested. Finally, it is investigated to what extent strongly lensed core-collapse supernovae could be used as an alternative approach for determining cosmological parameters.</p>

In the study of habitability of terrestrial exoplanets, both life-supporting conditions and the prevalence of transient life-threatening events need to be considered. One type of hazardous effect that has so far not received much attention is the thermal effect of a nearby active galactic nucleus (AGN), or in this particular case, the class of the AGN known as a quasar. In this work we investigate the thermal effect from a quasar by calculating the number of habitable terrestrial planets (HTP) in an elliptical or bulge-dominated galaxy, that goes extinct when exposed to the quasar radiation in a limited wavelength range. This is done by approximations and modelling along with pre-existing formulas and data from earlier publications. As a result, the influence by a quasar during the time span of quasar activity will have a less significant impact on the habitability in solar-type stellar systems than expected. Assuming tQSO = 108 yrs of quasar activity, results in the number of affected HTP, ≈ 1 × 105, 9 × 105 and 4 × 108 for isotropic spherical radiation and ≈ 1 × 106, 8 × 106 and 3 × 109 for a double-conical radiation. In terms of stellar mass fraction, ≈ 1.3%, 1.0%, 0.4% for isotropic radiation and ≈ 12.8%, 9.5%, 3.8% for conical, is affected. The results of this work are hoped to provide a rough estimation of the thermal impacts of a quasar on the habitability as well as to point out the most important parameters when considering this model. / I studier om beboeligheten på jordlika exoplaneter övervägs både förutsätningar för liv på planeten men även livshotande händelser i planetens närhet. En typ av farlig effekt som hit- intills inte fått mycket uppmärksamhet, är det termiska effekterna från en aktiv galaxkärna (AGN) eller som i detta fall, AGN-typen kvasar. I detta arbete studeras de termiska effekterna från en kvasar genom att beräkna antalet beboeliga jordlika exoplaneter (HTP) i en elliptisk eller bulge-dominerad galax, (bulge-centralförtätning), som blir obeboeliga då de utsätts för kvasarens strålning i ett begränsat våglängdsområde. Detta görs genom antaganden och modellering av redan befintliga formler och data från tidigare publikationer. Detta resulterar i en mindre inverkan av kvasaren på system kring sollika stjärnor än förväntat. Antaget tQSO =108 år av kvasar-aktivitet ger antal påverkade HTP, ≈ 1 × 105, 9 × 105 och 4 × 108 vid isotropisk strålning och 1 × 106, 8 × 106 och 3 × 109 vid dubbel-konisk formad strålning. Uttryckt i andel stjärnmassa motsvarar detta ≈ 1.3%, 1.0%, 0.4% för sfäriskt fall och ≈ 12.8%, 9.5%, 3.8% vid koniskt. Detta arbete hoppas kunna ge on grov uppfattning om kvasarens termiska effekter på beboligheten men även identifiera det mest betydande parametrarna i denna modell.

Some stars with similar properties to our sun (solar twins) have differ- ent chemical composition than the rest of the solar twins. One explanation might be planet engulfment. Therefore we did a large number of simu- lations where a disturbing star passed a sun and a planet at a distance closer than 100 AU to see how often the planet was engulfed. The result was that the planet in most cases was thrown out of the system, but it was engulfed in about 10 − 30% of the simulations when the planet was close to its star. The conclusion was that planet engulfment indeed can be a good explanation for the different chemical compositions of solar twins, at least in dense stellar clusters where such close passages should be quite common. / Vissa solliknande stja ̈rnor (s ̊a kallade soltvillingar) har en annorlunda kemisk sammansa ̈ttning ja ̈mfo ̈rt med resten av soltvillingarna. En mo ̈jlig fo ̈rklaring kan vara att dessa stja ̈rnor har slukat planeter. Da ̈rf ̈or gjorde vi ett stort antal simuleringar d ̈ar en sto ̈rande stja ̈rna passerade ett sys- tem best ̊aende av solen och en planet. Stj ̈arnan passerade p ̊a ett avst ̊and under 100 AU och vi observerade hur ofta planeten slukades. Resultatet var att planeten oftast slungades ut i rymden, men den slukades i 10-30% av simuleringarna da ̈r planeten kretsade na ̈ra sin stja ̈rna. Slutsatsen vara att planetslukning kan vara en rimlig f ̈orklaring till de annorlunda kemiska sammansa ̈ttningarna hos soltvillingar, ̊atminstone i ta ̈ta stja ̈rnhopar da ̈r na ̈ra stja ̈rnpassager bo ̈r vara ganska vanliga.

The object of this thesis is to extend the current tables for two useful quantities when calculatingcollisional broadening, the cross-section of interaction and the velocity parameter.These quantities, which have hitherto been tabulated for lower states, have now been calculatedfor higher lying states and are used in the ABO - model for spectral line broadening.Having larger tables for these values enables broadening calculations for more spectral linesand this thesis shows examples of calculations which beneted from this. During the calculationsof the tables some unexpected behaviour in the distribution of values arose whichhas not been seen previously. This could point to an unknown underlying mechanism.

New constraints on the scattering cross sections of the Kaluza Klein photon as a darkmatter candidate, its annihilation rate in the Sun and the resulting muon flux on Earth are derived.For this purpose, data collected in the IceCube Neutrino Observatory during 532 days of exposurein the austral winters between 2011 and 2014 have been analyzed with Poisson confidence intervals (J. Conrad et al., 2003) and compared to the simulated prediction achieved with the WimpSimsoftware (J. Edsjö et al., 2003). The results do not allow for any detection claim, but they improveby one order of magnitude the constraints formerly presented in R. Abbasi et al. (2010). Despitethe recent results from LHC experiment which discard lower masses for the Kaluza Klein photon (N. Deutschmann et al., 2017), the new constraints are still relevant for masses above 1500 GeV.

In this paper we analyze the small C1.5 class solar flare observed on June 30th 2013 by the Swedish Solar Telescope. The evolution of asym- metries in the H-alpha line profile of the solar flare was studied where it could be seen how the number of red asymmetric regions had a maximum value near the beginning of the flare and then decreases rapidly in the first 4 minutes of the observations. This could be interpreted as a correlation with the HXR and microwave emissions of the impulsive phase of the flare as these emissions also typically have a similar rapid increase and decrease of emission intensity.

In this thesis project, we study the field of high-dispersion spectroscopy and methods for extracting the spectrum of circumstellar objects such as exoplanets from the combined signal of a stellar system. One of the only techniques for detecting absorption lines in exoplanetary atmospheres is to directly image a planet and record the reflected light. However, exoplanets are incredibly faint compared to the parent star and are often completely obscured in any images of the system. We utilize techniques such as high-dispersion spectroscopy (HDS) and high contrast imaging (HCI) in order to capture the planetary signal and develop methods for reducing only the stellar light while leaving the planet relatively untouched.   We investigate a method for removing the scattered starlight by utilizing the separate spectra of the star and the planet, where the signal from the objects will be spread out according to a point spread function (PSF) and laid on top of each other. By empirically determining the shape of the stellar PSF, reference profiles can be created for each wavelength and subtracted from the entire signal, revealing the planetary spectrum. To achieve this, we have constructed a spectrum extraction algorithm, written in Python 3.6, for use on the spectra of directly imaged exoplanetary systems. Additionally, we discuss many of the problems which may arise when reducing cross-dispersed echelle spectra and attempt to solve them with the algorithm.   To assess our algorithm, we utilize spectral images of the system  Pictoris, taken with the high-dispersion spectrograph CRIRES, and three model exoplanetary systems of varying brightness. When extracting the spectrum of the planets, we find that the method employed for constructing the reference stellar PSFs is partially flawed and leaves a substantial amount of residual stellar light in the reduced images. This leads to difficulties with identifying any spectral absorption lines and an alternative method is likely necessary. Nonetheless, the algorithm is found to successfully extract the spectrum and identify spectral lines of an exoplanetary atmosphere if the planet is sufficiently bright, although only for theoretically unrealistic luminosities. We expect that our algorithm can be improved upon with more well-researched methods for reducing the starlight and by using data recorded with spectrographs of even higher dispersive capabilities, such as CRIRES+, METIS, or HIRES.