This project contains an exposition of the basics of General Relativity up to the study of Gravitational Waves. The goal is to apply this theory to understand binary systems, how they generate gravitational waves and the energy they lose in doing so. Gravitational waves have been a topic of interest in relativity ever since their theoretical prediction in 1916. Now the interest in the subject has been renewed since LIGO's announcement of the first detection of gravitational waves, proving once again the power of General Relativity. This topic is very promising because of its implications in the future of astronomy and cosmology as a new method to obtain information about our universe.

M dwarfs are abundant and long-lived stellar objects. The formation of planets around stars in stellar systems is believed to be metallicity dependent. To determine the metallicity with synthetic spectrum analysis, the elements producing the absorption lines ofthe spectra first have to be identified. The aim of this thesis is to identify and list the elements or molecules that produce the absorption lines in the spectra of Barnard's star. This thesis was done at the Division for Astronomy and Space Physics at Uppsala University. High resolution infrared spectral data recorded in the J band 1.1–1.4 μm was downloaded from the CRIRES-POP database. The data had to be wavelength corrected due to the effects of Doppler shift. A modified IDL program was used to read the data files,normalize the flux to unity and plot the spectra. This procedure was also done with the telluric spectra using data from a solar flux atlas. The IDL program plotted the normalized spectra together in the same plot. With this procedure the absorption features originating from the earth’s atmosphere could be identified and discarded. The analysis of the spectral lines resulted in wavelength values which were tested against the VALD3 database to determine what elements were possibly responsible for the absorption features. The results are presented in a line list. It can be used with other software programs to determine the metallicity. The identified elements and molecules agrees in part with earlier measurements of stellar spectra from M dwarf stars except for a number of lines where no matching elements were found in the VALD3 database. A line list with possible elements in the photosphere of Barnard’s star can be constructed from the spectra using high-resolution infrared spectroscopy. / M dvärgstjärnor är de mest förekommande stjärnorna i vår galax. De har en mycket långlivslängd, vissa tusen gånger längre än vår sol. Det finns teorier om att planetbildning runt stjärnor styrs av halten av ämnen som inte är väte eller helium. Denna halt kallas metallicitet. För att på konstgjord eller syntetisk väg bestämma metalliciteten i Barnard’s stjärna, en M dvärg, behöver de ämnen som bidrar till absorptionslinjerna i fotosfären först identifieras. Målsättningen med detta arbete var att identifiera de grundämnen och eventuella molekyler som skapar absorptionslinjerna i spektrumet till Barnard’s stjärna. Detta arbete utfördes på institutionen för fysik och astronomi. Metoden använde ett modifierat IDL program för att läsa och plotta data. Högupplöst infraröd spektraldata från Jbandet (1.1–1.4 μm) till Barnard’s stjärna hämtades från CRIRES-POP databasen och data för det telluriska spektrumet från en databas med telluriska linjer. Därefter plottades de samtidigt i ett våglängdsöverlappande normaliserat spektra. I programmet gick absorptionslinjer som inte hade sitt ursprung i jordens atmosfär att urskilja manuellt. Då våglängderna för absorptionlinjerna bestämts, matades värden in i databasen VALD3. Analysen av de returnerade värdena från VALD3 genererade en resultatlista med de mest sannolika elementen för de olika absorptionsvåglängderna. Resultatlistan kan användas som ingångsvärde till program som syntetiskt beräknar metalliciteten. Resultaten överensstämmer till viss del med tidigare mätningar. Slutsatsen är att metoden med högupplöst infraröd spektral data kan användas för att bestämma en lista med element och molekyler från fotosfären i Barnard’s stjärna.

This thesis describes the analysis of Very High Energy (VHE) emission from the Active Galactic Nucleus PKS 0537-441. It also aims to put the results in a wider context by implementing previous work done on this source. The data chosen for the analysis is provided by the Fermi-LAT satellite and covers the energy range between 300 MeV and 300 GeV. Initially a lightcurve of the received flux from the source was generated, containing data from August 2008 to April 2017, with a mean flux of 4∗10−8 photons per second per squared centimeter. The lightcurve contained sections of different flux intensities giving periods of special interest, such as a flaring period at August 2008 to August 2011, an enormous flare at April 2010 and a less active period between April 2013 - January 2016 that could be identified for further investigations. The differences in observed flux over time was tested and PKS 0537-441 was found to be a significantly variable source. Spectral Energy Distribution (SED) analysis was performed over both the entire period as well as over the selected subperiods and fitted against models using the tools provided by the Fermi Science Support Center (FSSC). The models used in the fitting was PowerLaw2, LogParabola and PLSuperExpCutoff and the best fit for the data was obtained from the PLSuperExpCutoff, except for the less intense period where the LogParabola gave the best fit. The result from the SED analysis was integrated with results from previous work done on the source, ranging over multiple wavelengths in order to get a SED which spanned over the entire electromagnetic spectrum. Finally, modeling of this multi wavelength SED was performed in order to obtain parameters for the physical processes involved in the creation of the radiation received from PKS 0537-441.

M dwarfs constitute around 70% of all stars in the local Galaxy. Their multitude together with their long main-sequence lifetimes make them important for studies of global properties of the Galaxy such as the initial mass function or the structure and kinematics of stellar populations. In addition, the exoplanet community is showing an increasing interest for those small, cold stars. However, very few M dwarfs are well characterized, and in the case of exoplanetary systems the stellar parameters have a direct influence on the derived planet properties. Stellar parameters of M dwarfs are difficult to determine because of their low surface temperatures that result in an optical spectrum dominated by molecular lines. Most previous works have therefore relied on empirical calibrations. High-resolution spectrographs operating in the infrared, a wavelength region less affected by molecular lines, have recently opened up a new window for the investigation of M dwarfs. In the two first papers of this thesis we have shown that we can determine the metallicity, and in some cases the effective temperature, using synthetic spectral fitting with improved accuracy. This method is time consuming and therefore not practical or even feasible for studies of large samples of M dwarfs. When comparing our results from the high-resolution studies with available photometric calibrations we find systematic differences. In the third paper we therefore used our sample to determine a new photometric metallicity calibration. Compared to previous calibrations our new photometric calibration shows improved statistical characteristics, and our calibration gives similar results as spectroscopic calibrations. In a comparison with theoretical calculations we find a good agreement of the shapes and slopes of iso-metallicity lines with our empirical relation. Applying the photometric calibration to a sample of M dwarfs with confirmed exoplanets we find a possible giant planet-metallicity correlation for M dwarfs.

We employ observational data about the largest cosmic void and most massive galaxy cluster known to date, the 'Cold Spot' void and the 'El Gordo' cluster, in order to constrain the parameter |fR0| from the f(R) gravity formulation by Hu and Sawicki and the matter power spectrum normalization at present time, σ8. We obtain the marginalized posterior distribution for these two parameters through a Markov Chain Monte Carlo analysis, where the likelihood function is modeled through extreme value statistics. The prior distribution for the additional cosmological parameters included in the computations (Ωdmh2, Ωbh2, h and ns) is matched to recent constraints. By combining the likelihood functions for both voids and clusters, we obtain a mean value log|fR0| = -5.1 ± 1.6, which is compatible with General Relativity (log|fR0| ≤-8) at 95% confidence level, but suggests a preference for a non-negligible modified gravity correction.

Ultraluminous X-ray sources (ULXs) are extragalactic, non-nuclear, point-like X-ray sources whose luminosity supersedes that of the Eddington limit of an accreting stellar mass black hole (L&gt; 10 ^ 39 erg / s). Most of them are powered by black holes and neutron stars undergoing genuine super-Eddington accretion, with a small handful of candidates being consistent with sub-Eddington accretion on an intermediate mass black hole. In this thesis, we explore the populations of ULXs in the sky surveys of ESA's X-ray satellite, XMM-Newton, and the MPE's newly launched X-ray telescope, eROSITA. We do so by correlating them with the HECATE list of galaxiesto build two X-ray non-nuclear catalogs, and comparing the yields with very expensive surveys and previous works. To build a catalog, we useother reference lists of contaminant objects, such as the Gaia data releases, the SIMBAD database or the SDSS survey to look for contaminating objects of diverse nature, such as foreground stars or background quasars, in order to make sure that our resulting ULX samples are as clean as possiblewith catalog data only. Our results include the attestation that the XMM-Newton ninth data release provides an improvement in quantity and quality with respect to older data releases used in previous works, and that the eROSITA survey is currently in a very preliminary stage. The two new catalogs contain 12,952 and 3,720 non-nuclear X-ray sources, out of which 914 and 132 are ULX candidates with an expected ~ 25% fraction of undetected contaminants. This constitutes a very significant contribution to the already known 300 ULX candidates. Since the sky coverage and depth of the XMM-Newton and eROSITA surveys are vastly different, only 19 of the ULX candidates are shared between the catalogs. ULX candidates are preferentially found in star-forming galaxies, but a subset of very bright objects (L&gt; 5x10 ^ 40 erg / s) try to be more common in elliptical galaxies, in contradiction to what has been established in the literature. / <p>This thesis was written under the joint supervision of Erin O'Sullivan at Uppsala University and Axel Schwope at the Leibniz Institute for Astrophysics in Potsdam. The presentation was held online due to the COVID-19 circumstances.</p> / Master Thesis

Exoplanet discovery has grown more quickly in recent years. However, the nature of their discovery leaves many unanswered in questions regarding exoplanetary habitability. Proxima Centauri b, an exoplanet which orbits the Sun's closest stellar neighbour, Proxima Centauri, was recently discovered with a subzero equilibrium temperature. Although not considered habitable based on the classical definition of the liquid water range, there may be fractions of Proxima Centauri b which are habitable. A prior study simulated the climate conditions of Proxima Centauri b until equilibrium was reached, using a variety of initial conditions. In this project, various metrics for calculating the fractional habitability of Proxima Centauri b are presented and applied to the results of the prior study's simulations. Colormaps are used to show the ice and temperature distributions that produce the calculated values of fractional habitability. The fractional habitabilities calculated show that while the value is both case and metric dependent, for the vast majority of all cases and metrics the value is nonzero implying that Proxima Centauri b is likely to have habitable regions. / Upptäckandet av exoplaneter har ökat i takt över de senaste åren. Samtidigt, på grund av sättet som de upptäcks finns många obesvarade frågor angående planeternas beboelighet. Proxima Centauri b är en exoplanet som kretsar kring solens närmsta granne, Proxima Centauri. Exoplaneten upptäcktes nyligen med en jämviktstemperatur under $0\degree$C. Trots att exoplaneten inte anses beboelig enligt klassisk definition kan det finnas delar av Proxima Centauri b som är beboeliga. En tidigare studie simulerade klimatförhållandena av Proxima Centarui b till jämvikt nåddes, med varierade begynnelsetillstånd. I detta projekt beräknas andelen av Proxima Centauri b som är beboelig genom flera olika mått för "fractional habitability". Måtten jämförs med den tidigare studien och dess simuleringar. Grafiskt åsikdligörs resultaten via färgkartor över planeten för istjocklek och yttemperatur. De beräknade värdena på Proxima Centauri b's "fractional habitability" påvisar beroende på mått och begynnelsetillstånd. Däremot, för en majoritet av både fall och mått är värdet nollskilt vilket antyder att Proxima Centauri b är delvist beboelig.

Since the construction of the IceCube Neutrino Observatory was completed in 2010, many amazing discoveries have been made in the field of neutrino physics. Recently a neutrino event has been linked to an blazar-type active galactic nucleus source, bringing us one step closer to understanding the production of high-energy extragalactic neutrinos and ushering in a new era of multimessenger astronomy. This was found by linking the neutrino event to one of the Fermi Collaboration’s gamma ray sources which had a blazar counterpart. The quest to link other neutrino events to AGN (active galactic nuclei) sources through collaboration with the Fermi Large Area Telescope has turned up some interesting candidates. The fact that some of these potential sources are not blazars is curious and, although unconfirmed as neutrino sources, these objects merit further investigation due to their unusual nature.

Astronomi fascinerar många och har spelat en avgörande roll i fysikens utveckling. I det svenska gymnasiets läroplan Gy2011 ingår astronomi i kursen Fysik 2. Tidigare intervjustudier har visat att lärare som undervisar i Fysik 2 ofta ger astronomidelen låg vikt och att den ofta knyts starkt till lärobokens innehåll. Det senare gör det intressant att granska hur de aktuella läroböckerna i Fysik 2 behandlar den astronomiska delen av denna kurs. I detta arbete granskas illustrationer ur astronomikapitlen i fyra läroböcker i Fysik 2 utgivna 2012-2019. För att avgöra vilka möjligheter illustrationerna erbjuder att urskilja detaljer som är relevanta för ämnet används begreppen affordans, disciplinär urskiljning och variation. Med dessa begrepp som stöd granskas ett urval av illustrationer (ett fotografi av den variabla stjärnan RS Puppis, bilder av Krabbnebulosan i olika våglängdsområden respektive tre versioner av hubblediagrammet). En del illustrationer visar sig ha lågt pedagogiskt värde, vilket beror på att de inte valts ändamålsenligt eller på att de kopplas svagt till omgivande text. Storleken hos synfältet i de sammanlagt 42 astronomiska bilder (t.ex. fotografier) som finns i kapitlen granskas också. Synfältets bredd i bilderna sträcker sig från 0,000002' till 120 grader (med medianvärdet 12') men synfältens storlek kommenteras inte i kapiteltexterna och variationen används inte för något pedagogiskt syfte.

Charge transfer reactions and their rates play a key role in correctly estimating element abundances in astrophysical objects such as supernovae. The reaction $C + O^+ \rightarrow C^+ + O(^1D) + \Delta E$ has been shown to be of significance when estimating oxygen abundances through model spectrum evaluations, and the relative rate of this reaction can under certain circumstances completely dictate the neutralization rate of oxygen ions. In this project, the rate of this reaction for four different temperatures is estimated using the Olson-Demkov model to calculate the cross section of the reaction as well as calculating rates for a few more reactions to compare to established literature values.  We find that the Olson-Demkov model produces good estimates for reactions that have small energy defects (within an order of magnitude of more rigorous quantum mechanical calculations), but the model underestimates the rate coefficient by several orders of magnitude as the energy defect increases. As the investigated reactions are all exothermic, the energy defect is the released energy from the reaction (i.e., the energy defect is positive). It is also found in most cases that the Olson-Demkov model rate is poorly estimated by the rate coefficient based only on the cross section at the mean velocity, caused by the cross section rising rapidly for velocities higher than the mean. The rate estimates produced for C+O$^+$ are also likely to be underestimated, especially for the temperatures 100 and 1000 Kelvin. No literature comparison is available for this specific reaction, but this conclusion is consistent with the other investigated reactions. / Supernovor är bland de mest extrema fenomen vi kan observera i hela Universum. Dessa våldsamma explosioner lämnar spår efter sig i många år och har varit ovärdeliga objekt att observera för att lära oss mer hur vår galax och Universum har utvecklats över tid. Ljuset från supernovor och deras kvarlevor kan analyseras för att ta reda på vad för ämnen som finns kvar eller som har bildats av både explosionen och de processer som ägt rum efteråt. En typ av reaktion som är viktig för att fullt ut förstå dessa miljöer är så kallade "laddningsöverföringar", en reaktion där en laddad och en oladdad partikel interagerar med varandra varvid laddningen förflyttas mellan de två. Detta projekt har fokuserat på en modell som avser att räkna ut uppskattningar på hur sannolikt det är för dessa reaktioner att äga rum. Modellen, som kallas för Olson-Demkov-modellen, har även jämförts med andra modeller för att se under vilka förhållanden som den fungerar.