We performed a double approach to better understand the formation process for high mass stars and their environments. First, we study and model an unique angular resolution and sensitivity an accretion disk around a 20 M☉. We use the standard flare disk models for Sun-like stars to scale-up their properties to high mass stars. Second, we study in a multi-wavelength, multi-scale approach the role of the magnetic fields around massive stars, focusing on the effect of the magnetic field in the core fragmentation process.
We use PAU Survey data to improve measurements of photometric redhifts
Extreme Mass Ratio Inspirals (EMRIs) are one of the main sources of gravitational waves for the future space-based gravitational-wave observatory that the European Space Agency will fly as its third L-class mission. This observatory, also known as LISA (Laser Interferometer Space Antenna), has the potential to detect the gravitational wave emission by EMRIs 1-2 years before the small compact object plunges into the (super)massive black hole. The length and complexity of the signals will allow for tests of the black hole paradigm as well as of the theory of gravitation.
The physics of extremely hot and/or dense relativistic plasmas is extremely rich. Quantum field theory computations for these systems have revealed to be cumbersome, as the standard quantum loop expansion valid at zero temperature ceases in this case to correspond to a gauge coupling constant expansion.In these plasmas there is a well-defined hierarchy of energy scales, defined by the temperature and/or chemical potential, as well as derived energy scales, obtained by multiplying the above by the gauge coupling constant. This fact gives the basic playground to use effective field theory techniques. In this thesis we will use and develop effective field theory techniques for the study of hot and/or dense plasma, and show how one can compute many properties of theses plasmasat high accuracy. Applications of these methods for both astrophysical and cosmological settings will be addressed.
The differential acceleration measurement between two free-falling test masses on-board LISA Pathfinder is limited in the low frequency regime by force noise applied to the test masses. Several effects can contribute as force noise on the inertial masses and, among them, magnetically-induced forces are precisely one of these effects limiting the perfomance of the instrument in the millihertz band. The origin of this disturbance is the coupling of the residual magnetisation and susceptibility of the test masses with the environmental magnetic field. In order to fully understand this term of the noise model, a set of coils and magnetometers are integrated as a part of the LISA Pathfinder diagnostics subsystem.
This theses describes the magnetic environment on-board and how are we modelling the different spacecraft contributions. We reporta as well on the magnetic experiments we have carried on board to determine the magnetic parameters of the Test Masses and the estimation of the magnetic contribution to the LISA Pathfinder noise spectrum.
La tesi utilitzarà dades obtingudes amb l’instrument CARMENES, que operarà entre el 2016 i el 2018 al telescopi de 3.5m de Calar Alto (Almeria). CARMENES és un instrument desenvolupat a través d’una col·laboració d’institucions alemanyes i espanyoles, format per dos espectrògrafs que permetran obtenir espectroscòpia d’alta resolució per a estrelles de massa baixa. S’espera poder derivar velocitats radials prou precises per a detectar el moviment keplerià causat per l’efecte gravitatori d’exoplanetes de tipus terrestre situats en la zona d’habitabilitat de les estrelles observades.
One of the fundamental goals of Cosmology is to understand how the Universe has evolved to form the distribution of large-scale structures that we observe today. Cosmological models can predict the properties of this distribution given certain values of the cosmological parameters like, for example, the expansion rate of the Universe, the dark energy density and the percentage of matter (dark matter and baryonic) with respect to the total energy density of the Universe. Over the past two decades, large galaxy surveys such as the Sloan Digital Sky Survey (SDSS; York et al. 2000), the WiggleZ Dark Energy Survey (Blake et al. 2011) and the Baryon Oscillation Spectroscopic Survey (BOSS; Dawson et al. 2013) have enabled to study in detail the large-scale structure of the Universe, and galaxy clustering has become a powerful tool to study galaxy formation and evolution and to tighten constraints on cosmological parameters. This data complements the information coming from cosmic microwave background (CMB) experiments, the most recent and with more quality being the ones collected by the Planck satellite, of the European Space Agency (ESA) (Planck Collaboration: Ade et al. 2015). Future galaxy surveys will cover a greater volume and will collect images of better quality than those obtained so far. This thesis aims to analyse the distribution of galaxies from the observations of future surveys in which the host group participates actively, such as the Dark Energy Survey (DES), the Dark Energy Spectroscopic Instrument (DESI), Physics of the Accelerating Universe (PAU) and the Euclid spatial mission from the ESA. For this purpose, during the thesis project we will develop numerical tools that allow us, in first place, to adequately model the observables with the complexity and detail needed to match the properties of future observations and, in second place, the optimal exploitation of such observations in order to obtain high precision limits to the values of cosmological parameters.
Thermal gradients on board the LISA Pathfinder mission can induce effects with a potential impact to perturb the main differential acceleration measurement between both free-falling test masses.
Temperature gradients across the housing induce forces through three different effects, namely asymmetric outgassing, radiation pressure and radiometer effect. The latter is related to the residual gas pressure around the test mass and, therefore, allows the estimation of the Brownian noise contribution, one of the limiting noise contributions for a future observatory like LISA.
Apart from thermal forces arising due to gradients around the test mass, thermo-elastic effects can also contribute to the instrument noise. There are two locations where such a distortion can be critical. First, the optical window, i.e. the interface between the optical bench and the test mass. This optical element –-the only not bonded on the Zerodur optical bench--- is clamped in a Titanium ring and therefore is susceptible to mechanical stress or changes in the refractive index due to thermal gradients across the glass. The second location are the struts holding the optical bench inside the thermal shield acting as the main thermal link to the outside (thermally noisier) environment. Temperature changes in these structures can induce net displacements or tilts of the bench with direct impact on the interferometer read-out.
This thesis describes the ultra-stable temperature environment on-board and report on the thermal experiments performed on-board to characterise these effects and estimate their contribution in the mission noise budget.