The aim of this project was to investigate the radial velocity variations of the Sun as observed from the Earth. This was accomplished by observing Doppler shifts of spectral lines in the region around 6300 Å. Telluric O2 lines were used as reference. The results indicate that during the day, the radial velocity increases and reaches a peak some time in the afternoon. Over spring, the radial velocity slowly declines. These results were compared to predicted values from JPL, NASA, and when accounting for the errors, they mostly agree with the predictions.

Understanding the cause of the accelerated expansion of the Universe is one of the most pressing issues in modern cosmology. An alternative to the LambdaCDM-model is bimetric gravity which is an extension of Einstein's theory of general relativity. In bimetric gravity there exists both a massive and massless graviton which gives rise to different phenomenology in a number of sectors. The LIGO observations of gravitational waves from binary mergers between black holes or neutron stars has opened up a new sector to test this theory in. We study the effects of the massive mode on the observed gravitational waveform. We place constraints on Fierz-Pauli mass, and the mixing angle between the massless and massive mode by using: (i) the observed LIGO waveform for GW150916 compared with the bimetric waveform which includes gravitational wave oscillations, (ii) absence of gravitational echoes, (iii) constraints on the luminosity distance, and (iv) constraints on the propagation speed of gravity. We note that the effects of dispersion on the massive wave packet which we detect as the echo can distort the waveform noticeably, hence it is possible that LIGO cannot detect it. Further investigation in this area is necessary. Lastly we investigate the stability of tensor perturbations in the early universe and the de Sitter point on sub- and superhorizon scales. The perturbations are found to be stable in all of these cases for all parameter values of the theory.

No description available.

The data reduction software of CRIRES+, a new high-resolution spectrometer installed at VLT, features a calibration routine that uses data from a Fabry-Pérot étalon. The quality of this calibration mode is assessed in this project report. Two investigations are carried out: From a diagnostics data set, the physical spacing between the three detector chips is reconstructed, as well as the étalon gap size as a function of Fabry-Pérot order. Both provide a measure of internal coherence of the calibration solution. The reconstructed detector spacing values are irreconcilable with the actual measured values, hinting at a fault in the calibration routine. The reconstructed gap curve shows unphysical discontinuities. Further investigation shows that each detector chip’s calibration solution seems to be consistent across it, while the three chips’ solutions are inconsistent with each other at several hundred meters per second. Due to ESO’s top-level requirements, this does not pose a technical fault. Yet, it still indicates significant room for improvement of the calibration routine.

Coronal mass ejections (CMEs) are considered the most energetic phenomenon in the heliosphere. Originated in the solar corona, they are formed by ejected plasma driven by strong magnetic fields. Studying the effects of CMEs on Earth and the interplanetary medium has become priority, since ground- and space-based technology can be affected by strong CMEs. Modeling of CMEs can provide an estimation of the arrival time, and WSA-ENLIL + Cone model is one of the most used models in space weather forecasting around the world. The WSA-ENLIL + Cone model is based on the characterization of the observed coronagraph image of a CME as a projected cone in the plane-of-sky (POS), the use of a synoptic magnetogram and the magnetohydrodynamical approximation to model CME events. In this project, we will study a particular event occurred on the 2021-11-03 and compare it with simulated data using the WSA-ENLIL + Cone model. The main objective is to study the input parameters of the model and assess the forecasting ability of the simulations. To do so, we have used in-situ data obtained from the Solar Orbiter spacecraft (SolO) and WIND spacecraft, that at the time of the event were located over the same line-of-sight, being located at 0.8 AU and the L1 Lagrange point, respectively. A total of 144 runs (divided in 6 ensembles of 24 simulated runs) were provided by the Met Office (UK) for each spacecraft location. Each simulation run has been generated using preset input parameters with small random variations and a different background synoptic magnetogram. Statistical analysis has been carried out, showing a linear relationship between the half-width and the arrival velocity of the CME. No particular relationship has been found between the input parameters and the time of arrival (ToA) of simulated runs, probably due to the small range of variation. Late initialized synoptic maps seems to produce better ToA prediction.

The renowned Omega Centauri (NGC 5139) is one of the most massive and complex known globular clusters in terms of multiple populations. In this project, we aim to investigate the chemical abundance of lithium in RBG stars in this cluster in pursuit of unraveling the that govern the formation of these distinct populations. By analyzing spectroscopic and photometric data, we determine the necessary stellar parameters and produce an algorithm that yields the Li abundance for each star, as well as its errors and an upper limit for the content of this element. This is followed by a comparison with the results obtained in Mucciarelli et al.(2018). Finally, we investigate how Li behaves within the different stellar populations of Omega Centauri using data from Milone et al. (2017a).

No description available.

This licentiate thesis gives an overview of modified gravity and primordial magnetic fields,bridged by gravitational waves (GWs) as a phenomenological probe of both sectors. First we derive the GW equation in a homogeneous and isotropic background from general relativity.This is followed by a brief review of modified gravity -- its motivations and some common approaches.Within the vast theory space of modified gravity, however, only a handful of parameters enter at the level of the GW equation, in a relatively model-independent manner. We then discuss a range of possible mechanisms giving rise to GWs in the early universe -- from inflation to the early radiation era -- and note, in particular, that magnetically-driven turbulence could be present regardless of the orders of the phase transitions.Therefore, the anisotropic stress due to primordial magnetic fields could be an ubiquitous category of production mechanisms for GWs,whose present-day relic spectrum could then be used to constrain the parameters of modified gravity, in addition to inferring the nature of the primordial magnetic sources themselves.

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.