Le milieu interstellaire est un élément essentiel des galaxies. Il est en effet la matrice de la formation des étoiles et des planètes. Il est composé de gaz et de poussières interstellaires. Il est généralement admis que la présence de molécules organiques complexes (COM) est due aux réactions en phase gazeuse. Toutefois, la synthèse de certaines espèces clés (i.e. H2,H2O, CO2, etc.) nécessite l'intervention des réactions en phase solide c'est à dire sur les grains de poussière. Plus de 200 molécules, dont des COM, ont été détectées dans l'ISM. et les enveloppes circumstellaires. Certaines de ces COM contiennent déjà du carbone, de l'oxygène, et de l'azote, qui sont les principaux éléments chimiques de la composition des molécules à partir desquelles la vie terrestre s'est construite. L'objectif de cette thèse est de comprendre les processus physiques et chimiques (diffusion, désorption et réactivité) qui se produisent sur les grains de poussière interstellaire. Plus spécifiquement, ma thèse se concentre sur l’étude de la désorption et de la réactivité des espèces azotées qui peuvent mener à des COM par des processus liés à l'hydrogénation. Toutes les expériences ont été réalisées avec l'expérience VENUS située au laboratoire LERMA à l'université de Cergy Pontoise, France. VENUS est composée d'une chambre à ultra-vide (UHV), appelée chambre principale, dotée d'une pression de base d'environ 10-10 mbar. Des atomes/molécules sont dirigées vers un porte-échantillon dans la chambre UHV au moyen d'un système à quatre faisceaux séparés. La température du porteéchantillon peut être contrôlée entre 7 K à 400 K. Les produits sont sondés par spectrométrie de masse et spectroscopie infrarouge par réflexion en adsorption. Différents environnements ont été utilisés : surface d'or ou substrats de glace d'eau (glace amorphe compacte ou poreuse et glace cristalline) pour imiter les différents environnements astrophysiques. Nous avons procédé à des expériences impliquant certains atomes et molécules comme l'hydrogène, le deutérium, l'oxygène, le CO, N2, NO, H2O, H2O, H2CO, CH3CN et CH3NC. Ces espèces ont été déposées sur une surface froide maintenue à 10 K (et jusqu'à 40 K). CO et N2 ont été déposés sur des substrats de glace d'eau pour étudier les différents comportements des adsorbats ainsi que la distribution des énergies de désorption et le mécanisme de ségrégation. Nous avons étudié l'efficacité de la pénétration des atomes (oxygène et hydrogène) dans la glace d'eau poreuse. Nous avons utilisé le NO comme traceur chimique. A partir de l'analyse de la consommation de NO, nous avons estimé la pénétration des atomes O ou D à travers la glace d'eau poreuse. Nous avons procédé à de nouvelles expériences sur l'hydrogénation du NO et nous avons constaté qu'il existe une barrière d'activation à l'étape HNO + H. Cependant, les atomes H peuvent traverser cette barrière d'activation par effet tunnel sur une surface maintenue à 8 K. Nous avons montré que l'hydroxylamine (NH2OH) est le principal produit de l'hydrogénation du NO à basse température, mais que le N2O est le principal produit à haute température. Nous présentons également les voies chimiques possibles de formation du formamide (NH2CHO) , molécule clé de la chimie pré-biotique, par co-hydrogénation de NO et de H2CO sur une surface froide (typiquement à 10 K). Nous avons analysé et montré l'efficacité de cette voie de formation du formamide sur les grains interstellaires. Nous avons montré que le réseau chimique de l'hydrogénation du CH3CN et du CH3NC est complexe et se fait par différents mécanismes qui sont en compétition. Nous avons mesuré et montré que l'hydrogénation est le mécanisme dominant. De plus, la présence de H2O augmente l'efficacité réactive. De nombreux processus chimiques en phase solide ont été simulés dans le contexte astrophysique de la formation de COM. / The interstellar medium is a key component of galaxies which is the matrixof the formation of stars and planets. It is composed of interstellar gas and dust grains. The presence of complex organic molecules (COMs) can be understoodvia reactions in the gas phase. However, the synthesis of some key species (i.e H2, H2O, CO2, etc) needs the intervention of the solid-state reactions on dust grains surface. More than 200 molecules including COMs have been detected in ISMand circumstellar shells. Some of these COMs already contain carbon, oxygen,and nitrogen, which are the main chemical elements in the composition of themolecules on which terrestrial life is built. The aim of this thesis is to understand physical and chemical processes (i.e diffusion, desorption, and reactivity) occurring on interstellar dust grains. More specifically, my thesis focuses on the investigation of desorption and reactivity of nitrogen bearing species that lead to COMs by hydrogenation related processes.All experiments were performed with the VENUS set-up located at the LERMACergy laboratory in the university of Cergy Pontoise, France. VENUS is composedof an Ultra High Vacuum (UHV) chamber, so called the main chamber, with abasis pressure around of 10 −10 mbar. Atoms/molecules were injected onto a sample holder in the UHV chamber through a separated four beamline system. The sample holder is controlled in temperature from 7 K to 400 K. Products are probed by using mass spectrometer and reflection adsorption infrared spectroscopy. Different solid states environments have been used: gold surface or water ice substrates (compact amorphous solid water, porous amorphous solid water, and crystalline ice) to mimic different the astrophysical environments.We proceeded experiments involving some atoms and molecules such as hydrogen,deuterium, oxygen, CO, N2, NO, H2O, H2CO, CH3CN, and CH3NC. These specieswere deposited on the cold surface held at 10 K (up to 40 K). CO and N2 weredeposited on water ice substrates to study different adsorbed behaviours as well as the distribution binding energy and the segregation mechanism. We studied theefficiency of atoms (i.e oxygen and hydrogen) penetration into porous water ice.We used NO as a chemical tracer for the penetration of O and H atoms throughwater ice. From the analysis of the consumption of NO, we estimated the penetra-tion of O or D atoms through porous water ice. We proceed new experiments onthe hydrogenation of NO and found that there is an activation barrier at HNO H step. However, H atoms can cross the activation barrier via quantum tunnelingon the cold surface maintained at 8 K. We indicated that hydroxylamine (NH2OH)is the major product of the hydrogenation of NO at low temperatures, but N2O isthe major product at high temperatures. We also present possible chemical path-ways of the pre-biotic formamide (NH2CHO) through the co-hydrogenation of NOand H2CO on the cold surface (typically at 10 K). Simultaneously, we analysedand discussed the efficient formation route of formamide on interstellar grains. We showed that the chemical network of the hydrogenation of CH3CN and CH3NC iscomplex and takes place via different mechanisms which tend to be competitive.We measured and indicated that the hydrogenation is the dominant mechanism.Furthermore, H2O is always raising the reactive efficiency.

<p> Gravitational waves in <i>f</i>(<i>R</i>) gravity excite monopole and m = 0&plusmn;2 quadrupole resonance modes of a spherical detector. This document reviews the basic ideas of general relativity and gravitational waves, and then applies those concepts to an <i>f</i>(<i> R</i>) gravitational wave. The acoustic response of a GW incident with a spherical detector is reviewed in detail, and the absorption cross section for an <i>f</i>(<i>R</i>) GW impinging on the spherical detector is calculated. Minimum detectable scalar wave amplitudes are explored for the Mario Schenberg detector. The mass of the scalar mode affects its detectability.</p>

The Ariel-6 spacecraft was launched during 1979 and remained operational for &sim; 3 years. The satellite payload is discussed, with an emphasis on the medium energy detectors, their calibration and performance. We present observations of spectral variability, in both galactic and extra-galactic sources, made with this instrument in the 1-50 keV energy range. Three galactic sources were observed, these consisted of two X-ray pulsators, 4U0115+63 and GX 1+4; the former being fortuitously seen during outburst. Both sources were found to show a significant phase dependence in their X-ray spectra. In GX 1+4 an Iron emission feature was detected, the equivalent width of which was also phase dependent. Pulse timing was performed on the data from both sources and in the case of 4U0115+63 yields a revised set of orbital parameters. The third galactic source presented is 3A1822-371, we find that our data are not only consistent with the presence of an accretion disc corona in the system, but strongly suggests the presence of such a corona in many disc fed systems. Three Seyfert galaxies, NGC 4151, MCG 8-11-11 and IIIZw2 were observed, this being the first reported X-ray spectrum of IIIZw2. NGC 4151 was found to have a spectrum consistent with that seen &sim; 3 years earlier, whilst MCG 8-11-11 was softer than seen hitherto and now shows evidence for an Iron emission line. The BL Lac, Mkn 421 was found to have a two component spectrum; comparison with earlier reported spectra indicates that both components vary independently of each other and therefore arise in physically differing regions of the source. Finally a forward-look is made which considers the improvements in medium energy spectroscopy that can be anticipated over the next decade or so.

X-ray emission from galactic supernova remnants X-ray images and spectra are used to determine the structure and physical conditions of shock heated interstellar gas and stellar ejecta within three galactic supernova remnants (SNRs). Parameters describing the initial supernova explosions (total energy, ejected mass) and ambient interstellar medium (density, homogeneity) are then derived. The interior density of the "middle-aged" SNR W44 is found to be fairly uniform, and inconsistent with the standard Sedov model, but similar to that predicted by models in which thermal conduction and/or heating and evaporation of engulfed, cold, interstellar clouds are important. This expanding bubble of hot, high pressure gas is likely to be an example of the formation of the hot component of interstellar medium, as detected in the vicinity of the Sun. In addition, it is likely that the SNR has collided with a nearby dense molecular cloud. The SNR W49B is found to be probably the remnant of a Type II supernova which occurred in a relatively dense medium 2000-5000 years ago. The abundance of hot iron in the ejecta is consistent with the cosmic value. The youngest SNR studied, SN1006, is found to be the remnant of a Type I supernova which occurred in a region of low, but fairly uniform (to within a factor of 2), interstellar density. Emission from reverse shocked ejecta may be most prominent in a limited area of the SNR, explaining a discrepancy between previous X-ray spectra of the remnant. A common result in all three SNRs is the detection of hot gas at their centres; the likely effects of a reverse shock and thermal conduction within SNRs are emphasized.

Studies of the electrodynamics of the high latitude ionosphere contribute to the understanding of the coupling between the solar wind, magnetosphere and upper atmosphere. This thesis describes an experimental investigation of high latitude E-region convection flows carried out with the Sweden And Britain auroral Radar Experiment (SABRE). The ionospheric observations have been related to satellite measurements of the interplanetary medium and hence interpreted in terms of models of solar wind-magnetosphere-ionosphere coupling processes. A close relationship has been established between various solar wind parameters and the daily mean SABRE backscatter intensity, a quantity which is rarely employed in geophysical studies. Empirical IMF-dependent models of the convection flows observed by SABRE are developed and statistical studies of the occurrence time of the Harang discontinuity are presented. High spatial resolution, two dimensional maps of the ionospheric projection of the dayside merging region, for both polarities of the azimuthal component of the IMF, are obtained for the first time. Two examples of strong nightside convection flows observed throughout the SABRE latitude range indicate that the convection flows may penetrate at least as far south as 61.5° N, geomagnetic latitude, during strongly northward IMF. The study indicates that, in the long term, the structure of the solar wind can be deduced from the mean backscatter intensity measured by a SABRE radar. In addition, the azimuthal component of the IMF exherts a crucial influence on the convection flows observed by SABRE in the cusp region. This effect is not confined to the noon sector but is also apparent in the vicinity of the Harang discontinuity. In general, the convection pattern exhibits a dependence on the north-south component of the IMF consistent with established reconnection mechanisms. However, there is evidence that existing models are insufficient to explain the anomalous convection flows observed under conditions of strongly northward IMF.

X-ray observations of three classes of interacting binary are presented. The systems studied are believed to be undergoing mass transfer by Roche lobe overflow onto a compact object. The observations were made between 1983 and 1989 with the EXOSAT and Ginga satellite observatories. The dwarf nova SS Cygni was subject to extensive monitoring using EXOSAT. In quiescence, the source has a hard spectrum which shows thermal iron K? and possibly K? emission. In outburst, emission is dominated by a soft component which emits at energies below &sim; 1 keV. This soft emission shows large amplitude, quasi-coherent sinusoidal modulation at periods in the range 7.4 to 10.8 sec. The evolution of the properties of this oscillation through outburst are studied in detail. A two day Ginga observation of the x-ray pulsar 1E 2259+586 is described. The pulse arrival times were searched for orbited modulation, and an upper limit (3?) to the projected semi-major axis was found to be ar sin i < 140 It-msec for periods from 1000 to 5000 sec. The source spectrum shows a broad line feature at &sim; 7 keV. It is suggested that this may arise from cyclotron processes. Details axe given of the Ginga observations of low mass x-ray binary systems which show 'dip' variability, the sources being XB 1916-053, XBT 0748-676, and X 1624-490. A re-analysis of the EXOSAT observations of X 1624-490 is also presented. Modulation in dippers arises from occultation of the compact x-ray emitting regions by structure in the accretion disc. Timing measurements constrain on the size of the emitting region and the distribution of the obscuring material. Spectral changes in dip events require a two-component model of absorption. By simulation, it is shown that this behaviour may arise from single component absorption if the column density changes rapidly. Revised estimates for the metal abundances of the three sources are given.

Near-infrared (1.2-2.2 micron) surface brightness measurements across the faces of a sample of nearby galaxies are presented, employing a variety of instrumental techniques. NGC 2683, 4565, and 5907 are seen almost edge-on, and for two of these, optical (V) data were obtained simultaneously with the infrared, using a widethrow-chop two channel photometer developed at Leicester by Dr. D.J. Adams. The results of these observations are presented in a single Chapter (3), in which the infrared measurements are used to define obscuration-free scale sizes for the disks, and the optical- infrared colours place constraints on possible mechanisms for the production of colour-index gradients. The remaining observational chapters (2 & 4) are a chronological record of use of the infrared system of the Anglo-Australian Telescope, documenting steps toward DC-mapping of extended objects, begun in 1980 with semi-DC observations of NGC 5128 at 2.2 microns (Chapter 2). Significant data were obtained in the course of these experiments, and in the final chapter we present J, H and K maps of M83, a large face-on spiral, which were obtained with the intention both of resolving the controversy over the Freeman Type I- Type II surface brightness profiles, and of detecting the density wave in the "old disk", suspected to drive the optical spiral star formation pattern. Our discussion of these observations also contains a number of warnings about the pitfalls which lurk in the DC-measurement process, most of which are concerned with the knowledge (or lack of it) of the sky background level when observing very extended objects. The first chapter gives a short introduction to some of the outstanding problems of extragalactic astronomy, and the uses to which infrared measurements can be put in tackling these problems. The overall objective of the Thesis is to illustrate, through observational results, the wide range of applications which near- infrared imaging finds in studies of galaxies. The contrast between the three observational chapters highlights this point.

The object of this thesis was to develop an imaging system using a CID Indium Antimonide (InSb) 33 element detector. Some interesting results were obtained on the rings of Saturn and the poles of Jupiter and the detector would have been used to scan the nuclear regions of galaxies. However, the array had a low sensitivity and a slow response which made it impractical to carry out any observations of galactic nuclei. Data, from single detector scans of NGC 2683, were provided by Dr. A. Adamson and Dr. D.J. Adams. These scans were performed to see if a halo exists around this galaxy. Two methods were used. The first was a deconvolution method which is shown to have a fault when deconvolving diffuse objects. The second method was to analyse the colour indices. This method indicated that there could be a spheroidal component causing the V-J colour to become redder out to approximately 90 arcseconds from the nucleus. Beyond 90 arcseconds, the colour becomes bluer possibly because the galaxy is not quite edge on and the blue disc begins to dominate the colour. The last chapter deals with the morphologically peculiar galaxies NGC 613, 1097, 1365 and 1808. The data on these galaxies were obtained on the AAT using a single detector which was scanned across the objects in a DC mapping mode. Maps were constructed, on a CYBER 73 at Leicester, from the J, H and K data. The data were then examined to see if these galaxies conform to the usual exponential disc and R1/4 laws. The three latter galaxies seem to exhibit nuclear colours similar to Seyfert's and NGC 613 may be either a weak active galaxy, or could just simply suffer from reddening.

Infrared and optical star counts have been obtained to investigate the stellar distribution in the plane of the Galaxy. The discovery of an obscured infrared cluster of sources is presented and a search technique for finding such obscured sources using visible and near-infrared plates is discussed. The techniques and mathematical treatment of star counting are described and, as an introduction, a literature review of the galactic structure is given. Optical star counts in a strip across the dark rift of the Galaxy, containing the line of sight to the galactic centre, indicate that the extinction in this direction starts to increase significantly at a distance of about 1500 pc, approximately at the distance of the Sagittarius arm. Counting the stars into reseau squares shows that the direction of the thickest extinction in the visible, for star counts to 18m .0, is not coincident with the plane of the Galaxy but about +1° in latitude away. Infrared star counts at 2.2 microns have been obtained for seven regions, spaced at 10o intervals, in the galactic plane. Away from the nucleus the star counts seem to fit a simple exponential disc model. At a longitude of 30o where the line of sight is tangential to a ring of molecular clouds, the disc population appears to be supplemented by an increase in density of late-type giants. Towards, the galactic centre the extinction at 2.2 microns is low enough for the dense core to be seen in the star counts, these dominating the star counts from the disc population.

In this thesis complete light curves, at both optical (V) and infrared (J, H, K) wavelengths, are presented for 15 pulsating variable stars. These include four dwarf Cepheids, six RR Lyraes and five Cepheids. In addition, radial velocity curves are also presented for three stars. Using this data, and existing radial velocity curves taken from the literature, we derive radii for all the stars using a variant of the Baade-Wesselink method. The value of the infrared for radius determination is illustrated by the fact that no previous attempts to apply Baade-Wesselink type methods, in an empirical manner, to short period (P <1 day) variables have been successful. From these results the following conclusions are drawn: 1. Metal poor RR Lyraes have ? 0.55 and the metal rich, shorter period variables appear to be &sim;0.3 - 0.4 mags fainter. These results and data secured recently for the globular clusters M5 and M107 show that RR Lyraes obey a period-luminosity relation in the infrared of the form = -1.01 - 2.80 log P The Cepheid period-luminosity relation from our data requires that the Cepheid zero point from cluster main sequence fitting should be reduced by ~0.1. With this revision a distance modulus of 18.50 +/- 0.15 for the LMC is given by both RR Lyraes and Cepheids. The "pulsation" masses of both the RR Lyraes and Cepheids are systematically smaller than the "evolutionary" masses by &sim;15%. The "pulsation" masses of dwarf Cepheids depend on the assumed pulsation mode. For those stars of known (or suspected) pulsation mode, low masses are derived. If this is generally true then dwarf Cepheids and delta Scutis are dissimilar. Further evidence in support of this conclusion is provided by, firstly, a comparison of the observed pulsation characteristics (periods and amplitudes) of the two groups of stars and, secondly, a comparison of the observed period changes of dwarf Cepheids with the theoretically calculated period changes.