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.

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.

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.

Globular Clusters contain very old metal-poor stars in different evolutionary stages evolved from the same primordial cloud. Signatures of atomic in stellar interiors are studied in the metal-poor GC M30. Furthermore, traces of cluster internal pollution depleting alpha elements e.g. Mg &amp; O are also found through high precision spectroscopy, which favors the existence of multiple stellar populations within a Globular Cluster. In this work, I use spectroscopic observations of 177 sample stars using the multi object spectrograph GIRAFFE and increasing the initial size of 12 of Scheutwinkel (2018) by 13 new UVES spectrograph sample stars of the Globular Cluster M30 ([Fe/H] = -2.3). The abundances of Fe, Ti, Mg &amp; Ba (GIRAFFE) and Fe, Na, Al &amp; Mg (UVES) are derived through the graphical spectrum analysis program SIU with VI broadband photometric stellar input parameters. The underlying line-formation theory is in LTE and uses 1-dimensional hydrostatic plan-parallel MAFAGS atmospheres with mixing length convection. We confirm an Al-Mg anti-correlation (Spearman ϱs= -0.583) and a correlation (Spearman ϱs= 0.641) between Al-Na in RGB stars as a direct result of being the partner elements of the depleted alpha elements Mg &amp; O caused through NeNa, ON and MgAl cycles. We find similar element ratios [X/Fe] as Carretta et al. (2018) &amp; O‘Malley et al. (2018) favoring the prior existence of multiple stellar populations within M30. Furthermore, we detected a signifcant restoration of abundances in the elements Fe, Mg &amp; Ba towards RGB stars. Fe, Mg and Ti are matching the predictions of the diffusion model T5.8 (Richard et al. 2005) reasonably well. For Ba, we have no current atomic diffusion modeling, so the validation of the results is not possible. The trend of Ti is v-shaped presumably due to stronger radiative accelaration effects for this element. Overall our relative abundance trends are consistent with other Globular Cluster studies by Gruyters et al. (2013&amp;2016), Korn et al. (2007) &amp; Lind (2007).

<p>The heating of the solar corona has been investigated during four of decades and several mechanisms able to produce heating have been proposed. It has until now not been possible to produce quantitative estimates that would establish any of these heating mechanism as the most important in the solar corona. In order to investigate which heating mechanism is the most important, a more detailed approach is needed.</p><p>In this thesis, the heating problem is approached ”ab initio”, using well observed facts and including realistic physics in a 3D magneto-hydrodynamic simulation of a small part of the solar atmosphere. The ”engine” of the heating mechanism is the solar photospheric velocity field, that braids the magnetic field into a configuration where energy has to be dissipated. The initial magnetic field is taken from an observation of a typical magnetic active region scaled down to fit inside the computational domain. The driving velocity field is generated by an algorithm that reproduces the statistical and geometrical fingerprints of solar granulation. Using a standard model atmosphere as the thermal initial condition, the simulation goes through a short startup phase, where the initial thermal stratification is quickly forgotten, after which the simulation stabilizes in statistical equilibrium. In this state, the magnetic field is able to dissipate the same amount of energy as is estimated to be lost through radiation, which is the main energy loss mechanism in the solar corona.</p><p>The simulation produces heating that is intermittent on the smallest resolved scales and hot loops similar to those observed through narrow band filters in the ultra violet. Other observed characteristics of the heating are reproduced, as well as a coronal temperature of roughly one million K. Because of the ab initio approach, the amount of heating produced in these simulations represents a lower limit to coronal heating and the conclusion is that such heating of the corona is unavoidable.</p>