Sunspot oscillations, intricate three-dimensional wave-like motions in the solar atmosphere, result from the complex interplay between plasma and magnetic fields. This study delves into the behaviour of these oscillations, exploring their simultaneous excitation and evaluating their impact on solar phenomena like coronal heating, energy transport, and solar flares. Utilising magnetohydrodynamic models, my work replicates and extends a computational study by Stangalini et al. I confirm the existence of multiple resonant modes inside the sunspot's umbra in active region AR 12546, characterised by a powerful magnetic field. I also demonstrate the model's sensitivity to the sunspot umbra's shape as it influences the physical characteristics of eigenfunctions. An extension of the study involves introducing an inhomogeneous distribution of the sound and Alfvén speed while assuming a vertical magnetic field. This advancement from a previously constant model yields substantial variations in results, notably distinguishing between slow and fast modes. The sound speed towards the sunspot centre notably constrains the slow modes. Additionally, analysing the power spectral density of vertical velocity in sunspots verifies the presence of five-minute oscillations, with more vital occurrences in the quiet sun and diminishing towards the centre of the sunspot. Examination of active region evolution over time reveals apparent magnetic polarity changes. This research significantly contributes to our understanding of sunspot dynamics. It introduces a novel model incorporating an inhomogeneous sound distribution and Alfvén speed, an advancement from prior approaches. This innovation adds depth to the comprehension of solar phenomena, paving the way for further investigations.

No description available.

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.