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In this thesis we consider perturbations of a perfect fluid on locally rotationally symmetrical (LRS) class II cosmological backgrounds, with a nonvanishing vorticity of the fluid on the perturbed model. The method used is based on the 1+1+2 covariant decomposition of spacetime, motivated by the assumption of anisotropic expansion, followed by a harmonic decomposition of all gauge invariant quantities. All perturbed quantities can be solved for in terms of the time evolution equations of eight harmonic coefficients. This set of eight harmonic coefficients decouple into an even and odd sector, containing five and three variables respectively, where the vorticity is represented as one variable in each sector. We find that the time evolution of the vorticity completely decouples from the other perturbed variables, and can be solved exactly by assuming a linear equation of state. The evolution of the remaining perturbed variables are examined in the geometrical optics approximation, and compared to research looking at the case when the vorticity vanishes on the perturbed model. The results turn out to be the same, except for a source term containing the odd parity of the vorticity in the evolution of the density, which act as a source term for the shear waves. The four remaining variables will represent damped, source free gravitational waves.

The very-high-energy gamma-ray emission of the hard spectrum BL Lac source 1H1914-194 has been studied with Fermi-LAT data covering a nearly ten-year period between August 2008 until March 2018 in the energy range of 300 MeV to 870 GeV. The mean flux has been determined as 8.4 x 10-9±3.5 x 10-10 photon cm-2 s-1. The data processing has been done with the Enrico software using the Fermi Science Tools (v10r0p5) and the Pass 8 version of the data, performing binned analysis in order to handle the long integration time. The lightcurve shows that the source has to be considered as variable in the given time period for a three-month binning. It gives furthermore evidence for at least one quiet and active period lasting slightly over 1.5 years each. Even these shorter periods show a weak variability. The significance of the source has been determined as σ = 57.5 for a one-year period. The spectral analysis of three different time periods have been fitted by PowerLaw2, LogParabola and PLExpCutoff functions resulting in LogParabola being slightly favored in most of the cases. However, the test statistic are not showing enough significance that may lead to an unambiguous preference. The data from the analysis has been implemented in a multiwavelength view of the source, showing that the analysis is in agreement with the data coming from the Fermi catalogs. The overall emission of 1H1914-194 has been modelled with theoretical frameworks based on a one-zone Synchrotron Self Compton (SSC) model providing an acceptable description of the SED.

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The cold dark matter (CDM) paradigm underlying the standard <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5CLambda" />CDM model of cosmology is successful on large scales but faces potential problems on small scales partly related to a seeming overproduction of dwarf galaxies. This could be alleviated in exotic dark matter models that suppresses small-scale structure formation. One such attractive model is known as fuzzy dark matter (FDM). FDM positsthat dark matter is composed of ultra-light bosons with masses <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?m_%7B%5Crm%20FDM%7D%20%5Csim%2010%5E%7B-22%7D" /> eV. With such light particle masses, quantum effects become important. More specifically, a pressure-like term appears in the equations of motion that counteracts gravitational collapse on small scales. Because small galaxies form first in CDM, it follows that the early history ot galaxy formation predicted by FDM should be markedly different. One novel way to probe this effect would be to use the 21 cm line of hydrogen which acts as a sensitive probe of the epoch of reionization (EoR) and Cosmic Dawn — when the first galactic sources of X-rays started to reheat theintergalactic medium (IGM). In this thesis, the evolution of the 21 cm signal have been simulated for both CDM and FDM. These simulations indicate that the fluctuationsin the 21 cm signal amenable to future observations are extremely weak (<img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Cll" /> 1 mK) — and probably unobservable — for FDM at high redshifts <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?z%20%5Csim%2015-16" /> compared to CDM (which tend to yield signals with amplitudes <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Cgg" /> 1 mK). This is mainly due to the delayed galaxy formation in FDM resulting in delayed Lyman-<img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Calpha" /> coupling of the 21 cm spin temperature to the kinetic temperature of the IGM. A robust prediction from all FDM scenarios explored in this thesis is that any detection of a signal at <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?z%20%5Csim%2015-16" /> would rule out interesting particle masses for FDM, and would be evidence for CDM-like structure formation. Future work that properly models ionization fluctuations during the EoR could also yield strong predictions at lower redshifts.

One method that can be used to identify the dynamic origin and specific parent bodies of Earth crossing meteoroids is the determination of the meteoroids’ orbital evolution. In this study, a Python-based program using the REBOUND software integration package to integrate meteoroid orbits backwards in time is developed. The program uses data from meteor observations made by the Swedish Allsky Meteor Network, and traces the distance and relative velocity between the meteoroid orbit and the orbits of selected parent body candidates backwards in time. The measure of these orbital differences is known as dissimilarity. The model is used to successfully reproduce the evolution of the Southworth-Hawkins dissimilarity criterion of the Annama meteorite and plausible parent body candidate 2014 UR116 presented by Trigo-Rodríguez et al (2015), as well as to determine plausible parent body associations of several meteors observed by the Swedish Allsky Meteor Network. Plausible parent bodies are presented in two new meteor cases, one of which confirms the parent body of the Geminid meteor shower. The model is concluded to be sufficiently accurate to motivate further use for meteoroid orbit integration purposes, and suggestions for future improvements are made. A new plausible parent body candidate for the Annama H5 meteorite is identified; the asteroid 2017 UZ44. In the case of one meteor event previously identified as a Perseid, the verification of the parent body is not successful using the developed model. In this case, no parent body candidate is found. Possible reasons for this are discussed. Moreover, the observational accuracy is found to be crucial if the program is to be used to study the meteor events observed by the network in detail, as the orbit has to be very well-constrained. / En metod som kan användas för att identifiera moderkroppar till meteoroider som äntrar jordens atmosfär är analys av meteoroidbanornas utveckling över tid. I denna studie har ett Python-baserat program som använder det numeriska integrationspaketet REBOUND för att följa meteoroidbanors utveckling över tid tagits fram. Programmet använder data från meteorobservationer som genomförts av det svenska meteornätverket Swedish Allsky Meteor Network och följer meteoroidbanors banutveckling i jämförelse med potentiella moderkroppars banutveckling över tid. För jämförelsen används Southworth-Hawkins-kriteriet. Modellen används för att framgångsrikt reproducera resultat presenterade av Trigo-Rodríguez et al (2015) genom att följa Annama-meteoritens banutveckling jämfört med banutvecklingen hos den möjliga moderkropp som presenteras i studien, asteroiden 2014 UR116. Modellen används också för att hitta möjliga moderkroppar för flertalet meteorer som observerats av det svenska meteornätverket. Möjliga moderkroppar presenteras i två fall, varav ett bekräftar moderkroppen för meteorregnet Geminiderna. Modellen verkar vara tillräckligt bra för att motivera användning vid integration av meteoroidbanor i syfte att identifiera moderkroppar genom att jämföra banornas utveckling över tid. En ny möjlig moderkropp presenteras för Annama-meteoriten; asteroiden 2017 UZ44. I ett fall har en meteor som observerats av det svenska meteornätverket tidigare klassificerats som en Perseid, men beräkningar genomförda med modellen framtagen i denna studie kan inte bekräfta resultatet. I detta fall återfinns ingen möjlig moderkropp för den specifika meteoren. Möjliga anledningar till detta diskuteras. Slutligen dras slutsatsen att mätosäkerheten i meteorobservationerna är vital för att meteoroidens bana ska vara tillräckligt välbestämd för att användas i syfte att analysera meteoroidbanornas utveckling över tid och hitta möjliga moderkroppar.

The Gaia space telescope is dedicated to monitor the sky, collect data and create the most precise 3D map consisting of more than 1.7 billion objects in the Milky Way. At the same time, the Radial Velocity Spectrometer (RVS) will collect spectra for ~150 million stars in the wavelength range 847 to 874 nm. This wave range is selected because it coincides with G-and K-type star energy-distribution peaks, as well as containing the strong Ca II infrared triplet lines (λ =8498, 8542, 8662 Å). The aim of this thesis is to create a grid of synthetic spectra in RVS wavelength range which later when compared to the real spectra can be used to determine the chemical composition of the star as well as precise atmospheric parameters. Calculations consist of 198 spectra ranging in effective temperature from Teff =4500 K to 7000 K with various steps, surface gravity log g = 2.5 to 4.5 with the step of 0.5and metallicities [M/H] = −0.5, 0.0 and 0.5 relative to the Solar composition. For calculations MARCS atmosphere models [3], a line list extracted from the VALD3 database [6] and the software SME [7] was used. Spectra calculations were conducted in both classical LTE and refined non-LTE modes for the line formation of calcium.

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