To reconstruct the history of the Milky Way, the chemo-physical characterization of stars is essential. For this, the chemical abundances of the Gaia Data Release 3 spectroscopy are of special importance, as they can be combined with dynamical properties in a chemo-kinematical analysis to find the relations between the chemistry and the Milky Way structure. This project explores nine abundance ratios in the DR3 and their evolution with the metallicity, distance to the galactic plane, azimuthal velocity, and eccentricity of the orbits of the stars.

Comprehending star formation in nearby galaxies is essential for deciphering the core mechanisms behind stellar birth. Using high-resolution CO line emission data from the Atacama Large Millimeter/submillimeter Array (ALMA), this research examines the CO excitation characteristics in two nearby star-forming galaxies, NGC 2903 and NGC 3627. We processed raw data cubes with pystructure, creating 2D moment maps to visualize CO ratios. High-resolution CO data from different rotational transitions (CO(1-0), CO(2-1), CO(3-2)) were used to study CO excitation. The study also incorporated stellar mass surface density and star formation rate (SFR) surface density maps to explore correlations between these properties and CO ratios. Using the Dense Gas Toolbox, we outlined the density structures of molecular gas, offering deeper insights into the underlying physical conditions influencing observed CO excitation patterns. We detected changes in CO line ratios that emphasize areas with elevated excitation conditions, suggesting higher gas density or temperature, which are closely associated with star formation activities. These variations suggest that non-thermal processes, such as collisions and radiation from stars, significantly influence CO excitation, as evidenced by the non-local thermodynamic equilibrium (non-LTE) excitation observed. Our findings indicate that the CO(3-2)-to-lower-J ratios are significantly affected by the SFR surface density, underscoring the influence of local star-forming environments on molecular gas excitation. Moment ratio maps display higher CO(3-2)/CO(2-1) ratios in the central regions of both galaxies, implying increased radiation and elevated temperatures in these zones. The connection between elevated CO ratios and regions with high SFR surface density further supports this relationship.x In contrast, stellar mass surface density appears to have a less pronounced effect on CO excitation, suggesting that local star formation processes, rather than large-scale galactic structures, predominantly drive the excitation conditions. This study highlights the importance of CO line ratios as diagnostic tools for understanding the excitation conditions of molecular gas in star-forming galaxies.

This project consists on the characterisation of the atmosphere of the exoplanet Wasp-107b, by observing the existence (or absence) of 4 different molecules: H20, CO2, CO and CH4.  To achieve this we use 2 algorithms:  - SYSREM, which eliminates the undesired stellar and thelluric features. -Cross-correlation, which compares the planetary spectrum with the molecules one. After applying these algorithms to 3 sets of simulations we can tell what mollecules are present in the planet's atmosphere.

<p>This thesis presents a brief review of gravitation and cosmology, and then gives an overview of the theory of cosmological perturbations; subsequently some applications are discussed, such as large-scale structure formation. Cosmological perturbations are here presented both in the Newtonian paradigm and in two di¤erent relativistic approaches. The relativistic approaches are (i) the metric approach, where small variations of the metric tensor are considered, and (ii) the covariant approach, which focusses on small variations of the curvature. Dealing with these two approaches also involves addressing the gauge problem –how to map an idealized world model into a more accurate world model.</p>

This thesis presents a brief review of gravitation and cosmology, and then gives an overview of the theory of cosmological perturbations; subsequently some applications are discussed, such as large-scale structure formation. Cosmological perturbations are here presented both in the Newtonian paradigm and in two di¤erent relativistic approaches. The relativistic approaches are (i) the metric approach, where small variations of the metric tensor are considered, and (ii) the covariant approach, which focusses on small variations of the curvature. Dealing with these two approaches also involves addressing the gauge problem –how to map an idealized world model into a more accurate world model.

Gamma-ray bursts (GRBs) are still puzzling scientists even 40 years after their discovery. Questions concerning the nature of the progenitors, the connection with supernovae and the origin of the high-energy emission are still lacking clear answers. Today, it is known that there are two populations of GRBs: short and long. It is also known that long GRBs are connected to supernovae (SNe). The emission observed from GRBs can be divided into two phases: the prompt emission and the afterglow. This thesis presents spectral analysis of the early X-ray afterglow of GRBs observed by the {\it Swift} satellite. For the majority of GRBs the early X-ray afterglows are well described by an absorbed power-law model. However, there exists a number of cases where this power-law component fails in fully describing the observed spectra and an additional blackbody component is needed. In the paper at the end of this thesis, a time-resolved spectral analysis of 74 GRBs observed by the X-ray telescope on board {\it Swift} is presented. Each spectrum is fitted with a power-law and a power-law plus blackbody model. The significance of the added thermal component is then assessed using Monte Carlo simulations. Six new cases of GRBs with thermal components in their spectra are presented, alongside three previously reported cases. The results show that a cocoon surrounding the jet is the most likely explanation for the thermal emission observed in the majority of GRBs. In addition, the observed narrow span in radii points to these GRBs being produced in similar environments. / <p>QC 20171031</p>

Ett av de mest notoriska dilemman i dagens kosmologi är den mörka materians natur och dess förekomst i universum. Mot bakgrund av detta har nya forskningsdiscipliner med rötterna i Einsteins relativitetsteori växt fram, bl.a. teorin om gravitationslinser som möjliggör en indirekt observationsmetod av ljussvaga kompakta objekt som annars skulle vara mycket svåra eller omöjliga att upptäcka på traditionella vis, såsom svarta hål. Via en genomgång av grundteorin för gravitationslinser, några enkla teoretiska studier och en grundläggande felmarginalsanalys illustreras hur olika typer av kompakta objekt i Vintergatans omedelbara omgivning kan ge upphov till vissa karakteristiska linsfenomen. Detta sätts i relation till rådande teorier om den tidigaste stjärnbildningen och de massiva kompakta rester som denna generation av mycket massiva stjärnor bör ha efterlämnat – i synnerhet intermediära svarta hål med massor på 100-1000 Msol som ännu kan finnas i dagens mörka galaxhalor. Sådana objekt kan komma att upptäckas i betydligt högre grad i framtiden med de observationstekniker som är under utveckling idag. / One of the most notorious dilemmas in cosmology today is the nature of dark matter and its distribution in the universe. Due to this, new research disciplines originating from Einstein’s theory of relativity have emerged, among them the theory of gravitational lensing which makes it possible to indirectly observe faint compact objects that would otherwise be very difficult or impossible to discover with traditional means, up to and including black holes. Through a rundown of the basic theory of gravitational lensing, a couple of simple theoretical models and an elementary error analysis, it is illustrated how different types of compact objects in the immediate vicinity of the Milky Way can yield various characteristic lensing phenomena. This is put in relation to contemporary theories regarding the earliest star formation and the massive compact remnants this generation of very massive stars should have left behind – particularly intermediate black holes with masses of 100-1000 Msun that may still be found in dark galactic halos of today. Such objects can contribute to future observations carried out with the observational technology being developed at present.

No description available.

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 Hα 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.

iPTF15dtg is a supernova (SN) Type Ic (lacking hydrogen and helium in its spectrum) with a light curve indicating that it is the result of a massive star explosion. Taddia et al. (2016) suggested that the progenitor star was a Wolf-Rayet (WR) star that previously suffered strong mass loss. More recent observations show that the SN light curve did not decline as expected, indicating the existence of an additional power source. One possibility is a magnetar, a hyper-magnetic neutron star capable of injecting its rotational energy into the light curve during relevant time scales. This bachelor thesis adds previously unpublished data to the iPTF15dtg light curve and compares simple semi-analytical models to rule out a radioactive scenario and discuss the possibility of a magnetar as the primary source of luminosity.