The presence of a magnetic field is shown to affect the evolution and properties of stars. Hence, it is necessary to observe different types of stars to explore these effects. The detached eclipsing binary UV Piscium is the object of interest in this study, where a first step of analyzing its global magnetic field is done. The observational data was collected during 2016, at the 3.6-m Canada-France-Hawaii Telescope at Mauna Kea, Hawaii. The analysis of the magnetic field is based on the line-addition technique least-squares deconvolution (LDS) of the polarisation signatures, and the aim is to search for circular polarisation signals produced by the Zeeman effect. The result shows a strong circular polarisation signature for the primary star of the binary, which is a direct evidence for the presence of a magnetic field. In contrast to this, the secondary star only shows a weak signal of circular polarisation in one of the analysed observations and further analysis of its magnetic field is needed. The secondary goal of the project was to calculate the stellar masses of the binary. This is done by measuring the radial velocities of the two stars via the line profiles, and preforming an orbital fit. The results gave: M1= 1.0211 ± 0.0040 Msol and M2 = 0.7728 ± 0.0028 Msol.

This thesis aims to give an introduction to quintessence models as well ascomparing those models with the currently accepted ΛCDM model. We willconsider quintessence in a spatially flat and isotropic Universe and useregular dynamical systems on a bounded three dimensional phase spacewhere we perform numerical calculations. This enables a globalunderstanding of these models and makes it possible to give thoroughdescriptions of the dynamics. We will discuss the three different types ofquintessence: Thawing, Scaling and Tracking quintessence and comparethem with the ΛCDM model. This thesis is based on several scientific papersand contains new numerical calculations and associated analysis. / Denna kandidatuppsats syfte är att ge en första inblick i kvintessens samtatt jämföra sådana modeller med den nuvarande accepterade ΛCDMmodellen. Vi studerar kvintessens i ett rumshomogent, isotropt och plantUniversum och använder reguljära dynamiska system i ett begränsattredimensionellt fasrum där vi utför numeriska beräkningar. Detta tillåter englobal undersökning av dessa modeller och gör det möjligt att noggrantbeskriva dynamiken. Vi diskuterar de tre olika typerna av kvintessens:”Thawing”, ”Scaling” och ”Tracking” kvintessens och jämför dessa medΛCDM modellen. Uppsatsen är baserad på flertalet vetenskapliga artiklaroch innehåller nya numeriska beräkningar med tillhörande analys.

An analysis is made on the Flat Spectrum Radio Quasar PKS 0426-380 using two sets of data. The first set of data is the Fermi-LAT data collected over the time 54682.66 − 59317.66 in Modified Julian Date within the energy range of 100 MeV to 500 GeV. The second set of data is a multi-wavelength spectral energy distribution within the approximate frequencies of <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%0A%0A%5Cleft%5B10%5E%7B10%7D,%2010%5E%7B27%7D%20%5Cright%5D" data-classname="equation" data-title="" />. First, the Fermi-LAT data were analysed and after modelling a lightcurve over the entire available time, a period of interest was located. The next step was to obtain a multi-wavelength spectral energy distribution of said period. Then, using JetSeT modelling, the data were analysed and a model of the Synchrotron Self-Compton, External-Compton and Synchrotron curves was fitted to the data. The final model which contained the best fit provided a set of physical parameters that described the source. These parameters were finally compared to two other Flat Spectrum Radio Quasars and conclusions regarding the properties of PKS 0426-380 were eventually drawn. A discussion comparing a related work on the same source to the results in this thesis followed. With the large differences in the constrained data between the Flat Spectrum Radio Quasars as background, three predictions concluded the thesis. These are, firstly, a cautioned approach to future searches for periodicity in AGN's. Secondly, in time, local periodicity for AGN's might be more common and interesting for future research. Finally, no certain values for the physical parameters of the AGN can be assessed and the results can only be wived as indications of the actual properties. / <p>Passed</p>

Clusters of Galaxies are amongst the largest gravitationally bound structures in our Universe and consist of thousands of galaxies. It is in these gigantic systems where Brightest Cluster Galaxies (BCGs) are found, the most massive galaxies in our Universe. A BCG, as its name indicates, is the brightest galaxy in a cluster. These enormous galaxies exhibit special properties, suggesting that they experience a different evolutionary path than a normal galaxy. It is widely accepted that their evolution involves merger events, when the BCG accrete another galaxy, as well as interaction events, like tidal stripping and/or removal of star-forming gas. However, the moment when those interactions happen in the life of the BCG and the extent of their impact on the BCG properties are still under discussion. This thesis aims to explore the later stages of BCG evolution by studying the merger/interaction fraction of BCGs in the local Universe. In particular, this research will explore the significance of correlations between the merger/interaction fraction with a variety of BCG properties (Metric Luminosity, α Parameter, BCG distance from the cluster center, BCG offset from the cluster mean redshift) and with a variety of cluster properties (cluster velocity dispersion, luminosity difference between the BCG and the second ranked galaxy in the cluster). The dependence of the merger/interaction fraction on the kinematics of BCGs is also investigated, using data for the BCG stellar velocity dispersion and for the local normalised velocity dispersion of galaxies within 50 kpc of the BCG. To accomplish these analyses, this thesis uses a sample of 432 BCGs at z ≤ 0.08 imaged as part of the Warpfire survey - an all-sky imaging and spectroscopic survey of BCGs in the nearby universe. Interacting and Non Interacting candidates are classified via a visual inspection of the residual images. This classification is performed by three independent people to ensure its robustness and to minimize classification bias. A merger/interaction fraction of fm/i = 0.220 ± 0.025 (stat) ± 0.040 (sys) at z ≤ 0.08 is found, with a lower limit of fmin ≥ 0.07 ± 0.01 (stat) ± 0.04 (sys). Significant correlations between the interaction status of BCG and its Metric Luminosity and α Parameter are also revealed. Specifically, the BCG merger/interaction fraction more than doubles in amplitude from ∼0.2 to ∼0.5 as the α Parameter increases from 0.4 to 0.9. However, those correlations do not appear to alter the Lm – α relationship, which remains robust against BCG interaction status. No significant correlation is found between the interaction status and the location of the BCG in the cluster, nor between the interaction status and the difference between the Metric Luminosity of the BCG and that of the second brightest galaxy in the cluster. However, it is found that BCGs with strong interaction residuals have slightly higher stellar velocity dispersions. Finally, the normalised velocity dispersion of galaxies within 50 kpc of the BCG is found to be lower than the normalised velocity dispersion around random galaxies in the outskirts of the cluster. The results of this thesis clearly indicate ongoing merger activity involving BCGs. The above results are consistent with idea that while BCG stellar accretion is not a dominant process at the current epoch it is not a negligible one either. These results also support a two phased growth model of BCG where the bulk of their stellar mass is assembled prior to z = 0.5 but still continues at a low level today.

In recent years, the increasingly precise constraints on the value of the Hubble constant, H0, have highlighted a discrepancy between the results arising from early-time and late-time measurements. A potential solution to this so-called Hubble tension is the hypothesis that we reside in a cosmic void, i.e. an underdense cosmic neighbourhood characterized by a faster local expansion rate. In this thesis, we model this scenario through the Lemaître-Tolman-Bondi formalism for an isotropic but inhomogeneous universe containing matter, curvature and a cosmological constant, which we denote by ΛLTB. We numerically implement this framework with two different formulations for the local matter density profile, respectively based upon a more realistic Gaussian ansatz and the idealized scenario of the so-called Oppenheimer-Snyder model. We then constrain the background cosmology and the void parameters involved in each case through a Markov Chain Monte Carlo analysis with a combination of recent data sets: the Pantheon Sample of type Ia supernovae, a collection of baryon acoustic oscillations data points from different galaxy surveys and the distance priors extracted from the latest Planck data release. For both models, the resulting bounds on the investigated parameter space suggest a preference for a -13% density drop with a size of approximately 300 Mpc, interestingly matching the prediction for the so-called KBC void already identified on the basis of independent analyses using galaxy distributions. We quantify the level of improvement on the Hubble tension by analyzing the ΛLTB constraints on the B-band absolute magnitude of the supernovae, which provides the calibration for the local measurements of H0. Since no significant difference is observed with respect to an analogous fit performed with the standard ΛCDM model, we conclude that the potential presence of a local void does not resolve the tension.

This project is an investigation of a cosmological model consisting of a five dimensional AdS-vacuum with a flux. By discharges in the flux, four dimensional bubbles can nucleate in the vacuum and collide with each other while expanding. Our observable universe is considered to be localized on the membrane of such a bubble. The main purpose of the model was to find a possible explanation for dark energy and inflation. We compute the Friedmann equation for an expanding bubble, as well as analytical expressions for the two slow roll parameters ε and η related to slow roll inflation. We also show that there exists a set of parameters of the model where both slow roll parameters are small enough in order for inflation to last for at least 60 Hubble times. However, our model doesn’t survive all consistency checks with today’s observations. We conclude that even if the resulting slow roll parameters look promising, one has to either look harder for a set of ”good” fundamental parameters of the model, or further develop it to have a chance of surviving all consistency checks. / Populärvetenskaplig sammanfattning: Det här projektet undersöker en kosmologisk modell bestående av ett femdimensionellt vakuum med negativ rumtidkrökning. I vakuumet finns ett elektriskt fält, som i högre dimensioner än fyra kallas flux (flöde). Urladdningar i detta flux gör det möjligt för fyrdimensionella bubblor att uppstå i vakuumet. Dessa vakuumbubblor expanderar snabbt och kommer så småningom att kollidera med varandra. Tanken är att vårt fyrdimensionella observerbara universum utgör en del av membranet på en av dessa expanderande vakuumbubblor. De andra vakuumbubblorna kan - om man vill - betraktas som parallella universum. Målet med detta projekt har varit att hitta en möjlig model för kosmisk inflation - epoken i vårt universums ungdom då rummet expanderade enormt snabbt under en väldigt kort tidsperiod. Inflationen i vår modell äger rum när vakuumbubblan för vårt universum kolliderar med andra vakuumbubblor. Vi lyckades visa att den här modellen kan ge upphov till inflation som varar tillräckligt länge för att det ska stämma överens med dagens observationer av vårt observerbara universum. Dock förutspår modellen även andra saker som inte stämmer överens med observationerna. Vår slutsats är att modellen ser lovande ut, men att man antingen behöver undersöka den noggrannare eller utveckla den på något sätt, om den ska ha en chans att stämma överens med universumet vi observerar. / <p>Presentationen skedde över videolänk på grund av Covid-19.</p>

The aim of this report is to explore different models of cosmology, depending on components as matter, radiation and dark energy. To be able to investigate the behaviour and age of these model universes, it is necessary to solve the Friedmann equation. Therefore a substantial part of this thesis is a study of general relativity, including mathematical tools as Riemannian geometry and the concept of curved space-time. / Denna rapport ämnar att utforska olika kosmologiska modeller beroende på innehåll som materia, strålning och mörk energi. För att undersöka beteendet och åldern av dessa modellerade universa så är det nödvändigt att lösa Friedmann-ekvationen. Därför ägnas en betydande del av detta arbete åt att studera allmän relativitetsteori, med matematiska verktyg som Riemanngeometri och konceptet krökt rum-tid.

It has been shown that ionospheric irregularities can disturb our GNSS (Global Navigation Satellite System) communication. This disturbance is caused by scintillation of the radio signals when they pass through the ionosphere, leading to lock-on difficulties or in worst case, a loss of position for the GNSS-receiver. In this study, a large number of ground based GNSS reference stations spread across Sweden (known as the Swepos-network) was used to measure the variability of the GNSS-signal. These measurements were then combined with observations of ionospheric irregularities made by the Langmuir probes on ESA’s SWARM satellites. The study is a collaboration between Uppsala University and the Swedish Institute of Space Physics and covers five events between December 2013 to Mars 2021, when both datasets were available. The purpose is to determine the shape and extension of these ionospheric irregularities and how localized in time and space they are. The study also tries to answer whether it is possible to draw any conclusions regarding physical models such as diffraction or refraction from this comparison. It was found that during the event days, there was in general a clear increase (of often several hundred percent) of the spatial variability on different scales according to the standard deviation. This increase was seen for both the lower orbiting SWARM A and C satellites and the higher orbiting SWARM B. It was also possible to see that the increase of spatial variability was spread across all the studied latitudes, (magnetic latitude 49° to 70°). This corresponds well with the fact that all the analysed event days had an GNSS-signal variability above average for the same latitudes. There seems to be a clear connection between increased GNSS-signal variability and ionospheric irregularities, although more studies need to be done to be able to draw more accurate conclusions.

In this thesis, we investigate the interaction between electromagnetic, gravitational, and plasma related perturbations on homogeneous and hypersurface orthogonal Locally Rotationally Symmetric (LRS) class II spacetimes. By using these spacetimes, which allow for the inclusion of a non-zero magnetic field, as backgrounds in a perturbative approach, we are able to see interactions between the electromagnetic and gravitational variables already to first order in the perturbations. This is in contrast to earlier works using isotropic Friedmann-Lemaı̂tre-Robertson-Walker (FLRW) backgrounds, where one is usually faced with going to second order in the perturbations. To get the equations governing our perturbations, we use a 1+1+2 covariant approach and gather relations from the Ricci and Bianchi identities, Maxwell’s equations, particle conservation, and energy-momentum conservation for the individual plasma components. After linearising these equations around a LRS background, performing a harmonic decomposition, and using the Magnetohydrodynamic (MHD) approximation for a cold plasma, we then arrive at a closed system for the first order perturbations. This system, consisting of ordinary differential equations in time and a set of constraints, is then reduced to two separate subsectors, containing seven and nine variables respectively. These variables include quantities related to the Weyl tensor, the vorticity, and the electromagnetic fields, as well as perturbations in the plasma velocity and energy density. Through numerical calculations, we use the equations for these variables to show that perturbations in the magnetic field can be sourced by perturbations in both the plasma velocity and the gravitational variables. We also observe beat-like interference patterns for large values of the Alfvén velocity. These results can be of interest when considering the large scale cosmic magnetic fields, as their origin still seems to elude us. However, since we neglect thermal pressures and dissipative fluxes, it should be noted that our results are mainly applicable in the limit of low temperature and in cases where the thermal pressure is smaller than the pressure due to the electromagnetic fields.

The interaction of supernova (SN) ejecta with the circumstellar medium (CSM) drives a strong shock wave into the CSM. These shocks are ideal places where effective particle acceleration and magnetic field amplification can take place. The accelerated relativistic particles, in the presence of magnetic field, could emit a part of their energy via synchrotron radiation in radio wavelengths. The flux of this radiation, when compared with observations, gives an estimate of the CSM density. This could either be the particle density ($\rm n_{ISM}$) in case of the SN exploding in a constant density medium, characteristic of interstellar medium, or pre-SN mass loss rate ($\mdot$) of the progenitor system for a wind medium. In this work we have modeled the synchrotron luminosities and compared that with the radio upper limits measured for the Type Ia SNe 2011fe and 2014J. Assuming equipartition of energy between electric and magnetic fields, with 10$\%$ of the thermal shock energy in each field, we found a very low density medium, having $\rm n_{ISM} &lt; \sim $ 0.35 $\ccc$,around both the SNe. In terms of $\mdot$ this implies an upper limit of $10^{-9}$ \msunyr for a wind velocity of 100 \kms. From the measurements of H I column density it could be expected that $\rm n_{ISM} \sim $ 1 $\ccc$ around both the SNe. If this is the true value close to the SNe, this would indicate that the energy density in magnetic field is less than that presumed for energy equipartition. The progenitors of both SNe 2011fe and 2014J are not clear. However previous studies have pointed toward a few potential  channels. Here, we have compared the CSM densities estimated by our models with that predicted by those different plausible formation channels and have tried to constrain the amplification of magnetic fields in SN shocks.