The current neutrino detectors have been able to detect neutrinos in the range of TeV to 100 PeV, however, ultra high energy (UHE) neutrinos above 100 PeV still remain to be detected. A new neutrino detector, the RNO-G, is currently being constructed in Greenland with the purpose of detecting the first UHE neutrinos using radio antennas capable of measuring the Askaryan pulse generated after a neutrino interaction with the ice molecules. To reconstruct the neutrino's properties from the antennas' output deep learning models have been used previously. In this work we present a Graph Neural Network capable of reconstructing the shower energy and neutrino direction with similar performance compared to Convolutional Neural Networks used in previous works, using a fraction of the training data. Additionally, an increase of the reconstruction performance is shown when using the full data set.

In an attempt to check published results on diffusion effects in M67 a non-LTE analysis is made on 28 high resolution FLAMES-UVES spectra of dwarfs and sub-giants around the turnoff point, where core hydrogen fusion halts. This analysis utilizes the software-suites LOTUS and iSpec to determine stellar parameters from equivalent-width measurements. With larger parameter scatter than expected diffusion effects were difficult to pin down. Eight spectra from either known variable stars (Kepler K2 data) or having low signal-to-noise data were therefore removed. This new reduced dataset confirms \citet{diffusionm672} that non-LTE analyses reduces scatter and makes diffusion trends easier to identify. This may however also be the result of systematic errors in LOTUS and requires more (and independent) confirmation. / För att undersöka publicerade diffusionseffekter i M67 genomförs en analys utan LTE av 28 högupplösta FLAMES-UVES spektra av dvärgar och subjättar runt turnoffpunkten. Med programmen LOTUS NLTE och iSpec bestämdes atmosfäriska parametrar från uppmätta linjestyrkor. Initialt fanns det en stor spridning i de erhållna paramternarna, vilket gjorde det svårt att dra slutsatser om diffusion. Åtta spektra från antingen kända variabler (Kepler K2-data) eller med låg signal till brus togs därför bort. Detta nya reducerade dataset verkar bekräfta \citet{diffusionm672} att icke-LTE minskar spridning och gör diffusionstrender mer lättidentifierade. Resultatet kan dock vara ett resultat av systematiska fel i LOTUS och behöver därmed ytterliggare bekräftas.

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.

<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.</p><p>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 <em>intermediära svarta hål</em> med massor på 100-1000 M_sol 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. </p> / <p>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.</p><p>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 <em>intermediate black holes</em> with masses of 100-1000 M_sun 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.</p>

<p>Molecular spectroscopy at radio wavelengths is a tool well suited for studying the composition and outgassing kinematics of cometary comae. This is particularly true for distant comets, i.e. comets at heliocentric distances greater than a few AU, where the excitation of molecules is inefficient other than for rotational energy levels. At these distances, water sublimation is inefficient, and cometary activity is dominated by outgassing of carbon monoxide.</p><p>An observing campaign is presented, where the millimeter-wave emission from CO in comet 29P/Schwassmann-Wachmann 1 has been studied in detail using the Swedish-ESO Submillimetre Telescope (SEST). Coma models have been used to analyse the spectra. The production of CO is found to have two separate sources, one releasing CO gas on the nuclear dayside, and one extended source, where CO is produced from coma material, proposed to be icy dust grains.</p><p>Radio observations of many molecules in comet C/1995 O1 (Hale-Bopp) have been carried out in a long-term international effort using several radio telescopes. An overview of the results is presented, describing the evolution of the gas production as the comet passed through the inner Solar system. Spectra recorded using the SEST, primarily of CO, for heliocentric distances from 3 to 11 AU are analysed in detail, also using coma models.</p><p>The concept of icy grains constituting the extended source discovered in comet 29P/Schwassmann-Wachmann 1 is examined by theoretical modelling of micrometre-sized ice/dust particles at 6 AU from the Sun. It is shown that that such grains can release their content of volatiles on timescales similar to that found for the extended source.</p>

<p>The dynamical evolution of the spin axis direction due to gravitational and thermal factors is examined. It is found that the spin axis variations generally are regular and relatively small for the bodies in the asteroid main belt. There are also reasons to believe that this is the case for minor objects beyond the main belt. However, it is found that these regular variations are larger when the orbital inclination of the objects is increased. This effect may explain certain features in the spin vector distribution of the main belt asteroids, not possible to explain by collisional factors. The spin vector evolution of the asteroids in the inner solar system, including the Earth- and Mars-crossing objects, is often subjected to strong forces related to frequencies in the orbital evolution. The variations in the spin vector direction are then very large and often subjected to chaos. The larger frequency related obliquity zones of the Mars-crossers are usually regular while the zones of the Earth-Mars-crossers often are of a chaotic nature. The spin vector evolution of asteroids with comet-like orbits is often chaotic regardless of initial obliquity. For the inner solar system asteroids, it is often possible for an initial prograde spin to turn into a retrograde one, or vice versa, due to the frequency related phenomena. Though some spin vector directions seem to be more probable than other ones over time, there are no indications for an evolution towards a more prograde or a more retrograde spin vector distribution.</p><p>The effects on the spin vector evolution from the thermal Yarkovsky force are examined for objects with radii larger than 50 m. This force will affect the orbital evolution and thus indirectly affect the spin vector evolution. However, it is found that the studied effects are minor as compared to the gravitationally related ones. This is true both for the diurnal and the seasonal variants of the Yarkovsky force.</p>

Molecular spectroscopy at radio wavelengths is a tool well suited for studying the composition and outgassing kinematics of cometary comae. This is particularly true for distant comets, i.e. comets at heliocentric distances greater than a few AU, where the excitation of molecules is inefficient other than for rotational energy levels. At these distances, water sublimation is inefficient, and cometary activity is dominated by outgassing of carbon monoxide. An observing campaign is presented, where the millimeter-wave emission from CO in comet 29P/Schwassmann-Wachmann 1 has been studied in detail using the Swedish-ESO Submillimetre Telescope (SEST). Coma models have been used to analyse the spectra. The production of CO is found to have two separate sources, one releasing CO gas on the nuclear dayside, and one extended source, where CO is produced from coma material, proposed to be icy dust grains. Radio observations of many molecules in comet C/1995 O1 (Hale-Bopp) have been carried out in a long-term international effort using several radio telescopes. An overview of the results is presented, describing the evolution of the gas production as the comet passed through the inner Solar system. Spectra recorded using the SEST, primarily of CO, for heliocentric distances from 3 to 11 AU are analysed in detail, also using coma models. The concept of icy grains constituting the extended source discovered in comet 29P/Schwassmann-Wachmann 1 is examined by theoretical modelling of micrometre-sized ice/dust particles at 6 AU from the Sun. It is shown that that such grains can release their content of volatiles on timescales similar to that found for the extended source.

The dynamical evolution of the spin axis direction due to gravitational and thermal factors is examined. It is found that the spin axis variations generally are regular and relatively small for the bodies in the asteroid main belt. There are also reasons to believe that this is the case for minor objects beyond the main belt. However, it is found that these regular variations are larger when the orbital inclination of the objects is increased. This effect may explain certain features in the spin vector distribution of the main belt asteroids, not possible to explain by collisional factors. The spin vector evolution of the asteroids in the inner solar system, including the Earth- and Mars-crossing objects, is often subjected to strong forces related to frequencies in the orbital evolution. The variations in the spin vector direction are then very large and often subjected to chaos. The larger frequency related obliquity zones of the Mars-crossers are usually regular while the zones of the Earth-Mars-crossers often are of a chaotic nature. The spin vector evolution of asteroids with comet-like orbits is often chaotic regardless of initial obliquity. For the inner solar system asteroids, it is often possible for an initial prograde spin to turn into a retrograde one, or vice versa, due to the frequency related phenomena. Though some spin vector directions seem to be more probable than other ones over time, there are no indications for an evolution towards a more prograde or a more retrograde spin vector distribution. The effects on the spin vector evolution from the thermal Yarkovsky force are examined for objects with radii larger than 50 m. This force will affect the orbital evolution and thus indirectly affect the spin vector evolution. However, it is found that the studied effects are minor as compared to the gravitationally related ones. This is true both for the diurnal and the seasonal variants of the Yarkovsky force.

The predicted primordial lithium abundance differs from observations of unevolved halo stars on the Spite plateau by a factor two to three. Surface depletion due to atomic diffusion has been suggested as a cause of this so-called cosmological lithium problem. Evolutionary abundance trends indicative of atomic diffusion have previously been identified in the metal-poor globular cluster NGC 6397 ([Fe/H] = -2), with stellar parameters deduced spectroscopically in a self-consistent manner. Abundances of five elements (Li, Mg, Ca, Ti, and Fe) were found to be in agreement with stellar structure models including the effects of atomic diffusion and a free-parameter description of turbulent mixing at the lowest efficiency compatible with the flatness of the Spite plateau. It is our aim to evaluate the interplay of modelling assumptions and theoretical predictions under various priors, e.g. the independent age determination using the white dwarf cooling sequence, and the high efficiency of turbulent mixing recently found compatible with halo field stars. We perform self-consistent spectroscopic abundance analyses at an expanded effective temperature scale inspired by results of new photometric calibrations from the infrared flux method. The resulting abundances are compared to predictions in a grid of theoretical isochrones, chosen in light of the priors for age and efficiency of turbulent mixing. We find that the observed abundance trends are not artefacts of the effective temperature scale, as it cannot be arbitrarily modified to flatten all trends. The inferred abundance trends seem to be in agreement with predictions for an age compatible with the white dwarf cooling sequence, and a limited range of weak turbulent mixing. The inferred initial lithium abundance of these stars is merely 30 % lower than the primordial abundance, discrepant at 1.5 standard deviations. Hence, a stellar solution to the cosmological lithium problem is still within reach.