Le satellite Fermi a été lancé le 11 juin 2008, avec à son bord le Large Area Telescope (LAT). Le LAT est un télescope sensible au rayonnement gamma de 20 MeV à plus de 300 GeV. Au début de l'activité de Fermi, neuf pulsars jeunes et énergétiques étaient connus dans le domaine gamma. Le nombre de détections de pulsars par le LAT prédit avant lancement était de plusieurs dizaines au moins. Le LAT permettait également l'étude des pulsars milliseconde (MSPs), jamais détectés avec certitude à très haute énergie jusqu'alors. Cette thèse aborde dans un premier temps la campagne de chronométrie des pulsars émetteurs radio et/ou X, candidats à la détection par le LAT, en collaboration avec les grands radiotélescopes et télescopes X. Cette campagne a permis la recherche de signaux gamma pulsés avec une grande sensibilité. En outre, la plupart des MSPs galactiques ont été suivis dans le cadre de cette campagne, sans biais de sélection a priori sur cette population d'étoiles. Pour la première fois, des pulsations ont été détectées pour huit MSPs galactiques au-dessus de 100 MeV. Quelques bons candidats à une détection prochaine apparaissent. Une recherche similaire a été conduite pour des MSPs d'amas globulaires, sans succès à présent. L'analyse des courbes de lumière et des propriétés spectrales des huit MSPs détectés révèle que leur rayonnement gamma est relativement similaire à celui des pulsars ordinaires, et est vraisemblablement produit dans la magnétosphère externe. Cette découverte suggère que certaines sources non identifiées sont des MSPs, pour l'instant inconnus.

<p>The <em>IceCube telescope</em> is built within the ice at the geographical South Pole in the middle of the Antarctica continent. The purpose of the telescope is to detect muon neutrinos, the muon neutrino being an elementary particle with minuscule mass coming from space.</p><p>The detector consists of some 5000 DOMs registering photon hits (light). A muon neutrino traveling through the detector might give rise to a track of photons making up a straight line, and by analyzing the hit output of the DOMs, looking for tracks, neutrinos and their direction can be detected.</p><p>When processing the output, triggers are used. Triggers are calculation- efficient algorithms used to tell if the hits seem to make up a track - if that is the case, all hits are processed more carefully to find the direction and other properties of the track.</p><p>The Track Engine is an additional trigger, specialized to trigger on low- energy events (few track hits), which are particularly difficult to detect. Low-energy events are of special interest in the search for Dark Matter.</p><p>An algorithm for triggering on low-energy events has been suggested. Its main idea is to divide time in overlapping time windows, find all possible pairs of hits in each time window, calculate the spherical coordinates θ and ϕ of the position vectors of the hits of the pairs, histogram the angles, and look for peaks in the resulting 2d-histogram. Such peaks would indicate a straight line of hits, and, hence, a track.</p><p>It is not believed that a software implementation of the algorithm would be fast enough. The Master's Thesis project has had the aim of developing an FPGA implementation of the algorithm.</p><p>Such an FPGA implementation has been developed. Extensive tests on the design has yielded positive results showing that it is fully functional. The design can be synthesized to about 180 MHz, making it possible to handle an incoming hit rate of about 6 MHz, giving a margin of more than twice to the expected average hit rate of 2.6 MHz.</p>

All future Extremely Large Telescopes (ELTs) will be segmented. However, as their size grows, they become increasingly sensitive to external disturbances, such as gravity, wind and temperature gradients and to internal vibration sources. Maintaining their optical quality will rely more and more on active control means. This thesis studies active optics of segmented primary mirrors, which aims at stabilizing the shape and ensuring the continuity of the surface formed by the segments in the face of external disturbances. The modelling and the control strategy for active optics of segmented mirrors are examined. The model has a moderate size due to the separation of the quasi-static behavior of the mirror (primary response) from the dynamic response (secondary, or residual response). The control strategy considers explicitly the primary response of the telescope through a singular value controller. The control-structure interaction is addressed with the general robustness theory of multivariable feedback systems, where the secondary response is considered as uncertainty. Scaling laws allowing the extrapolation of the results obtained with existing 10m telescopes to future ELTs and even future larger telescopes are addressed and the most relevant parameters are highlighted. The study is illustrated with a set of examples of increasing sizes, up to 200 segments. This numerical study confirms that scaling laws, originally developed with simple analytical models, can be used in confidence in the preliminary design of large segmented telescopes.

A search for weakly interacting massive particles (WIMPs) annihilating in the Sun was performed with the IceCube and AMANDA neutrino telescopes, using data from 2008 corresponding to 149 days of livetime. Assuming that particles in the dark matter halo scatter and accumulate in the centre of the Sun, Majorana WIMPs may pair-wise annihilate and give rise to a neutrino signal detectable in an experiment at Earth. No excess of muon-neutrinos from the Sun was observed, and limits on the νμ-flux were set for masses between 50 GeV and 5 TeV considering WIMPs annihilating into b‾b and W+W-. Separate limits were also calculated for the case of the lightest Kaluza-Klein particle. The flux limits were converted to limits on the spin-dependent and spin-independent WIMP-proton cross sections, σSD and σSI. The search was combined using a joint likelihood method with AMANDA and IceCube data from 2001-2007, yielding the 90% CL upper limits Φμ &lt; 103 km-2y-1 for a WIMP mass of 1000 GeV and σSD &lt; 1.28×10-4 pb for 250 GeV, both for the W+W- spectrum. / IceCube

This thesis presents a study of the wind load forces and their influence on the response of structures. The study is based on the capacity of the Proper Orthogonal Decomposition method (POD) to identify and extract organized patterns that are hidden or embedded inside a complex field. Technically this complex field is defined as a multi-variate random process, which in wind engineering is represented by unsteady pressure signals recorded on multiple points of the surface of a structure. The POD method thus transforms the multi-variate random pressure field into a sequence of load shapes that are uncorrelated with each other. The effect of each uncorrelated load shape on the structural response is relatively easy to evaluate and the individual contributions can be added linearly afterwards. Additionally, since each uncorrelated load shape is associated with a percentage of the total energy involved in the loading process, it is possible to neglect those load shapes with low energy content. Furthermore, the load shapes obtained with the POD often reveal physical flow structures, like vortex shedding, oscillations of shear layers, etc. This later property can be used in conjunction with classical results in fluid mechanics to theorize about the physical nature of different flow mechanics and their interactions. The POD method is well suited to be used in conjunction with the classical modal analysis, not only to calculate the structural response for a given pressure field but to observe the details of the wind-structure interaction. A detailed and complete application is presented here but the methodology is very general since it can be applied to any recorded pressure field and for any type of structure.

This thesis presents a study of the wind load forces and their influence on the response of structures. The study is based on the capacity of the Proper Orthogonal Decomposition method (POD) to identify and extract organized patterns that are hidden or embedded inside a complex field. Technically this complex field is defined as a multi-variate random process, which in wind engineering is represented by unsteady pressure signals recorded on multiple points of the surface of a structure. The POD method thus transforms the multi-variate random pressure field into a sequence of load shapes that are uncorrelated with each other. The effect of each uncorrelated load shape on the structural response is relatively easy to evaluate and the individual contributions can be added linearly afterwards. Additionally, since each uncorrelated load shape is associated with a percentage of the total energy involved in the loading process, it is possible to neglect those load shapes with low energy content. Furthermore, the load shapes obtained with the POD often reveal physical flow structures, like vortex shedding, oscillations of shear layers, etc. This later property can be used in conjunction with classical results in fluid mechanics to theorize about the physical nature of different flow mechanics and their interactions. The POD method is well suited to be used in conjunction with the classical modal analysis, not only to calculate the structural response for a given pressure field but to observe the details of the wind-structure interaction. A detailed and complete application is presented here but the methodology is very general since it can be applied to any recorded pressure field and for any type of structure.

The IceCube telescope is built within the ice at the geographical South Pole in the middle of the Antarctica continent. The purpose of the telescope is to detect muon neutrinos, the muon neutrino being an elementary particle with minuscule mass coming from space. The detector consists of some 5000 DOMs registering photon hits (light). A muon neutrino traveling through the detector might give rise to a track of photons making up a straight line, and by analyzing the hit output of the DOMs, looking for tracks, neutrinos and their direction can be detected. When processing the output, triggers are used. Triggers are calculation- efficient algorithms used to tell if the hits seem to make up a track - if that is the case, all hits are processed more carefully to find the direction and other properties of the track. The Track Engine is an additional trigger, specialized to trigger on low- energy events (few track hits), which are particularly difficult to detect. Low-energy events are of special interest in the search for Dark Matter. An algorithm for triggering on low-energy events has been suggested. Its main idea is to divide time in overlapping time windows, find all possible pairs of hits in each time window, calculate the spherical coordinates θ and ϕ of the position vectors of the hits of the pairs, histogram the angles, and look for peaks in the resulting 2d-histogram. Such peaks would indicate a straight line of hits, and, hence, a track. It is not believed that a software implementation of the algorithm would be fast enough. The Master's Thesis project has had the aim of developing an FPGA implementation of the algorithm. Such an FPGA implementation has been developed. Extensive tests on the design has yielded positive results showing that it is fully functional. The design can be synthesized to about 180 MHz, making it possible to handle an incoming hit rate of about 6 MHz, giving a margin of more than twice to the expected average hit rate of 2.6 MHz.

How galaxies form and evolve is one of the primary outstanding problems in extragalactic astronomy. I conduct a quantitative census of the relative importance of the major structural components (flattened and dynamically cold disk-dominated components versus puffy and dynamically hot spheroidal or triaxial bulges/ellipticals) in massive galaxies over cosmic time and across different environments in order to explore how galaxies evolve under the action of the various assembly mechanisms (major mergers, minor mergers, gas accretion, and internal secular processes) in these different regimes. I perform three inter-related analyses focusing on massive galaxies from z ~ 0 - 3 in both field and rich cluster environments. Important strengths of this thesis include the use of high-resolution, panchromatic imaging from some of the largest and deepest galaxy surveys with the Hubble Space Telescope (HST), Spitzer, and Chandra space telescopes, and also the inclusion of detailed comparisons between the empirical data and hierarchical ΛCDM-based models of galaxy evolution. / text

The success of asteroseismology lies in the correct identification of the normal modes of oscillation. The Whole Earth Telescope (WET) identified the normal modes of a helium white dwarf pulsator, GD358, by analyzing the period distribution of the pulsation modes. Another way to identify modes is by comparing pulsation amplitudes in the UV to the optical. To cross-calibrate the two mode identification methods, we observed GD358 in August, 1996 with the Hubble Space Telescope (HST) to obtain the UV data while observing nearly simultaneously from the ground. During our observations, GD358 went through a very drastic amplitude modulation in a time scale of hours. These short time scale amplitude changes made the direct UV to optical amplitude determinations difficult. We successfully eliminate the possibility that the 423s mode, the dominant mode at the time of these observations, is an l=3 or 4 g-mode pulsation, but we cannot unambiguously decide if it is an l=1 or 2. Theoretical calculations indicate that the massive pulsating DA white dwarf BPM 37093 has a crystallized interior (Winget et al. 1997; Kanaan 1996; Montgomery 1998). Crystallization was predicted theoretically 40 years ago (Kirshnitz 1960; Abrisokov 1961; Salpeter 1961) although uncertainties in the nature and extent of crystallization, as well as its associated effects, are the largest sources of uncertainty in calculating the ages of the coolest white dwarf stars- important chronometers of the galactic disk. The WET observed BPM 37093 in April 1998 and again in April 1999, simultaneously with the HST, in hopes of using both the period distribution and the amplitude comparison method to identify the l value of the modes and measure the first crystallized mass-fraction of a stellar interior. Here we also rule out the possibility of the observed modes being l=3 and higher and demonstrate that not all the observed modes are l-1. If all the observed modes are l-2, then we conclude that the crystallization mass fraction is between 0-80%, depending mainly on the surface H layer. In the end, we evaluate the amplitude comparison method and address advantages and problems using this method compared to other mode identification methods. / text

A search for Weakly Interacting Massive Particles (WIMPs) annihilating in the dark matter halo of the Milky Way was performed, using data from the IceCube Neutrino Observatory and its low-energy extension DeepCore. The data were collected during one year between 2011 to 2012 corresponding to 329.1 days of detector livetime. If WIMPs in the dark matter halo undergo pairwise annihilation they may produce a neutrino signal detectable at the Earth. Assuming annihilation into bb, W+W-, τ+τ-, μ+μ-, νν and a neutrino flavor ratio of 1:1:1 at the detector, cascade events from all neutrino flavors were used to search for an excess of neutrinos matching a dark matter signal spectrum. Two dark matter density profiles for the halo were used; the cored Burkert profile and the cusped NFW profile. No excess of neutrinos from the Galactic halo was observed, and upper limits were set for the thermally averaged product of the WIMP self-annihilation cross section and velocity, &lt;σAv&gt;, in the WIMP mass range 30 GeV to 10 TeV. For the bb annihilation channel and the NFW halo profile, the 90% C.L. upper limits are 9.03×10-22 cm3 s-1 for the mass WIMP 100 GeV and 4.08×10-22 cm3 s-1 for the WIMP mass 3000 GeV. The corresponding upper limits for the μ+μ- annihilation channel are 4.40×10-23 cm3 s-1 and 3.20×10-23 cm3 s-1. / IceCube