In this report calibration of the four probes attached onto the JUICE spacecraft has been made.The JUICE spacecraft (JUpiter Icy Moon Explorer) is a spacecraft which will investigate theenvironment on and around Jupiter and its four biggest moons. On the spacecraft are 10different instruments onboard, where one of the instruments is the Radio and Plasma WaveInvestigator (RPWI). The mission of RPWI is to measure the electromagnetic field and plasmaparticles, among other things around the Jovian system. To analyse the measured data fromthe probe, the data has to be calibrated. In this report test data and raw flight data of the probeshas been calibrated by digital-analog converting the signal. The data SID 1 and SID 3, whichboth measure the electric field, the calibration was successful both for the ground test data andthe raw flight data. However, the calibration of SID 2, which measure the plasma density, didnot give the calibrated analog signal within expected range. Possible sources of error for thatdeviation includes error in the Fourier Transform of the transfer function. The raw flight data forSID 1 and 2 was further disturbed by solar wind, resulting in high measured signals for theelectric field and the plasma density. For future improvements this calibration method could berepeated on another set of data without disturbance to verify the calibration method and identifypotential source of error.

In this report, we constrain properties of foreground objects in the Milky Way that have the potential of being confused with accretion disks of Population III stellar- mass black holes at high redshift. Following Windhorst et al. (2018), a model for multicolour accretion disks of Population III stellar-mass black holes is presented. The resulting spectra are used to derive observable magnitudes with the James Webb Space Telescope (JWST). Magnification of a factor 103 to 106, depending on the black hole mass, through gravitational lensing is necessary to surpass the JWST detection limit. Spectra of faint Milky Way objects of low-mass main sequence or pre-main sequence stars (Baraffe et al. 2015) and cool brown dwarfs and giant exoplanets (Phillips et al. 2020) were fitted to a distance such that their observable JWST magnitudes are similar to those of the accretion disk. We find that the spectral energy distributions that have the highest chances of being confused with high redshift Population III black hole accretion disks belong to pre-main sequence and low-mass main sequence stars of temperature 1500 K to 4200 K. At redshift 𝑧 = 7, accretion disks most closely resemble the spectral energy distributions of 2830 K Milky Way objects. Cool brown dwarfs or giant exoplanets with chemical equilibrium atmospheres at temperature ∼ 2700 K or chemical non-equilibrium atmospheres at ∼ 1790 K most closely resemble the spectral energy distribution of redshift 𝑧 = 7–8. Although the SEDs produce good fits, a confusion probability can sometimes be reduced because the models are very young (0.5 to 10 Myr) or have distances corresponding to the stellar halo (≳ 200 kpc).

In this project, we investigate the plasma heating associated with coherent structures, such as current sheets and vortices, in different solar wind conditions: slow solar wind, stream interaction regions, and heliospheric current sheets, observed by the Solar Or- biter mission. To unravel this mystery, we first use the Partial Variance of Increment method [1] to locate these coherent structures. We then employ correlation functions to determine the coexistence of these structures and investigate the global elevation of plasma temperature [2]. Additionally, we employ a quantitative analysis of conditioned PVI [3] to examine the local increase in plasma temperature [4]. The results clearly indicate that plasma heating takes place at and near these struc- tures. Specifically, current sheets locally heat the plasma, while plasma vortices have a global impact on heating. A characteristic timescale of approximately 200 seconds emerges, separating the local heating of coherent structures from other heating sources. In slow solar wind and stream interaction regions, we observe clusters of coherent structures with sizes ranging from 4 to 6 hours, underlain by a scale of 1 to 2 hours. The heliospheric current sheet does not exhibit such modulation. These coherent struc- ture clusters are embedded within larger macroscopic structures spanning 12 to 24 hours.

In this thesis, we study slowly rotating relativistic stars by modeling them as perfect fluids. The Hartle formalism is used to perturb a spherically symmetric static solution into slow rotation and the corresponding field equations to second order are presented. Five of the seven equations form a subsystem that decouples and can thus be solved independently. It is solely this system we focus on in this work. Two new variables are introduced to rewrite the field equations such that they become algebraic in one of the variables, the other one is used as a generating function and can be chosen to generate desired perfect fluid configurations. To adapt for numerical integration, the field equations are further reformulated as a coupled system of ordinary differential equations, which is solved numerically using a fourth order Runge-Kutta method. Two choices of the generating function are examined, namely a simple polynomial case as well as the Kuch2 III solution, and the related field equations are solved to find the perturbative functions. By studying physical quantities such as the pressure, energy density and speed of sound to zeroth order, we show that both of the studied configurations correspond to physically realistic solutions within a range of parameter values. Additionally, the shape of the zero pressure surface to second order is analyzed and found to be oblate for both cases, which coincides with the expected shape of a rotating fluid. We also investigate whether the Petrov type D condition is fulfilled, and the results indicate that both solutions fail to satisfy the condition and are thus not of Petrov type D. Moreover, it is shown that both the polynomial case and the perturbed Kuch2 III solution can be matched to a suitable asymptotically flat vacuum exterior, using the Darmois-Israel procedure. It should be noted that even though we are solely examining the slowly rotating limit, our results are in fact valid even up to fairly high rotational velocities. This indicates that the perturbative generating method of this thesis may be used to produce models describing physically reasonable configurations, e.g. rotating neutron stars.

No description available.

This thesis introduces briefly physical processes operating in the ISM around massive starsand focuses on the impact strong stellar feedback has in creating large-scale structures in a galaxy.Stellar feedback is ubiquitous in star forming galaxies and its effect on the ISM depends strongly on the energy output from the most massive stars (M$\geq$7 \Mo ) and the properties of the surrounding gas. Starburst galaxies are among the most active in producing %galaxies are among the most active galaxies and produce a large amount of massive star clusters %or even super star clusters (SSC; M$_{cl} \geq 10^5$ \Mo ), with stellar populations up to thousands of massive stars. %The most massive stars (M$\geq$30 \Mo ) are lives short, but they In the first 4 Myr of the star clusters evolution, radiative feedback of the most massive stars (M$\geq$30 \Mo ) are at work. Large amount of ionizing photons are released to the ambient medium while radiative pressure compress the surrounding gas. At the same time their stellar winds inject continuously mechanical energy and momentum in their surrounding. This mechanical feedback is then at later ages, until $\sim$ 40 Myrs, maintained by supernova explosions from the less massive stars. Strong stellar feedback tends to develop large-scale structures such as bubbles, loops, filaments and outflows. These are transient structures and can be seen as imprints of how the released energy is clearing or has cleared paths in the ISM. Strong stellar feedback can have devastating consequences in dwarf galaxies due to their shallow gravitational potential. It can accelerate outflows with velocities larger than their escape velocities. In this way, dwarf galaxies can lose a large fraction of their gas mass, which will be crucial in their subsequent evolution.On the other hand, galactic winds might be responsible to create holes in the ISM, allowing the easily-absorbed ionizing photons (Lyman continuum photons, LyC) to escape the galaxy. Studies on a few LyC leaking galaxies have shown that this mechanisms might have preference from a density-bound scenario, which takes place in galaxies with a highly ionized halo. In my paper I used deep MUSE observations to analyse the impact strong stellar feedback has in the starburst and Lyman continuum emitting galaxy: Haro 11. The paper presents three emission line diagnostics aiming to analyse the condition of the warm ionized gas in this galaxy, which are the \Ha\ emission, the level of ionization in gas and the presence of fast shocks. These diagnostics are presented in maps of 50 \kms\ bins in a velocity range from -400 to 350 \kms . Haro 11 shows a violent ISM whose warm ionized gas is almost completely shaped by effect of stellar feedback from the most massive star forming regions in the centre. Arcs, shells, outflows paths and galactic scale ionizing cones are imprinted in ISM of Haro 11. Our analysis suggests the presence of a kpc-scale superbubble which might have created galactic holes in the ISM. Beside of that, Haro 11 shows a highly ionized halo. Both mechanisms appear to facilitate the escape of LyC in this galaxy. %Finally, we observe emission at velocities up to thousand \kms\ which could hints to gas escaping the galaxy. Finally the paper presents estimates of the gas mass fraction that could escape the gravitational potential of the galaxy.

No description available.

No description available.

No description available.

In this thesis, we have constructed new analytical solutions for initial data of the Einstein equations. Such solutions are valuable for gaining a better understanding of problems involving strong gravitational and/or electromagnetic interactions in general relativity. In this process, we have examined an inhomogeneous cosmological model consisting a lattice of regularly arranged, charged black holes with initial data corresponding to the maximum expansion of a cosmological solution. We have also refined the method in such a way that the values of the mass and charge of the sources can be prescribed beforehand subject to certain constraints dictated by the field equations. Then we studied a two dimensional 'equatorial' cross-section of the initial data space and presented the behaviour of the local curvature for the slices of the Platonic bodies 8, 16, 24, 120 and compared black hole lattices with a Friedmann universe of a unit radius. We see that the black hole lattice is not close to this, or any other, round sphere as far as its local curvature is concerned. For all Platonic solutions, the black hole regions are located where the curvature assumes its minimum value, and it strikes the eye that they are well isolated from each other and do not distort each other noticeably. On the other hand, we confirm that black holes themselves are remarkably round in the strong curvature regions. The recent surge of interest in these solutions was driven by the cosmological averaging problem. Is it likely to affect our understanding of the dark side of the universe in a significant way? We feel that the right way to go may well be to find other interesting toy models, where agreement can be reached quickly.