This thesis presents the design, calibration, and performance evaluation of a type of two-hole pressure probe anemometer known as a Conrad probe, as well as its subsequent implementation on an autonomous, compact boundary layer measurement device and its first application for subsonic in-flight measurements of a swept wing boundary layer. Calibration of the Conrad probe was accomplished using two calibration functions and a non-nulling method for resolving in-plane flow velocity direction and magnitude over a range of ±30 degrees. This approach to calibration and application offered the advantages of rapid data acquisition with lower energy consumption than alternative methods for pressure probe anemometry in swept wing boundary layers. Following calibration, the probe was adapted for use on an autonomous boundary layer measurement device including development of revised software. Utilizing this setup, boundary layer measurements were obtained on both swept and unswept models in a wind tunnel with a maximum operational velocity of 110 mph corresponding to a dynamic pressure of 30 psf. The wind tunnel results showed that the Conrad probe could measure in-plane flow magnitude for both laminar and turbulent boundary layers with sufficient uncertainty and spatial resolution for its intended application in flight testing. The Conrad probe and boundary layer measurement system were then employed for flight tests of a 30 degree swept wing model carried beneath an aircraft at a flight Mach number of 0.52 and altitudes up to 44,000 ft. The flight test results from the Conrad probe allowed for the successful determination of overall boundary layer thickness, laminar/turbulent conditions, and degree of flow turning within the boundary layer. It is believed that the rapid data acquisition and low energy consumption of the Conrad probe implementation on the boundary layer measurement system make it a good alternative for future flight testing requiring measurements of in-plane flow velocity magnitude and direction.

La détection des exoplanètes et de l’environnement d’étoiles jeunes tel que les disques de débris fait face à deux difficultés majeures : d’une part, la faible distance angulaire entre le compagnon (ou le disque) et son étoile hôte, et d’autre part, le contraste élevé entre les deux composantes en terme de flux. L’interférométrie est une des techniques permettant de palier ces deux problématiques en apportant une détection à la fois à haute résolution angulaire et à haute dynamique. C’est tout particulièrement le cas dans la mise en oeuvre de l’interférométrie annulante, aussi appelée interférométrie en frange noire, lors de laquelle on vient éteindre le flux de l’étoile principale grâce aux propriétés de cohérence de la lumière.On recombine la lumière issue de deux télescopes ou plus de sorte à faire interférer destructivement les photons provenant de l’étoile principale et constructivement pour les photons venant du compagnon ou du disque environnant. Mon travail de thèse s’inscrit dans ce cadre, avec l’étude de données observationnelles de huit disques de débris réalisées au Very Large Telescope, grâce à la technique interférométrique de masquage de pupille. Lors de cette étude j’ai réalisé la réduction des données interférométriques et une analyse des termes de clôtures de phase. Puisque aucun compagnon n’a été détecté dans les données, j’en ai déduit les limites de détection en termes de luminosité et de masse estimée à l’aide d’isochrones issue de modèle d’évolution.Ma thèse à également consisté en une composante expérimentale, avec la conception et l’étalonnage de l’instrument FIRST-IR (Fibered Imager foR a Single Telescope InfraRed) en laboratoire, à l’Observatoire de Meudon. Cet instrument est un interféromètre qui associe la technique de réarrangement de pupille fibré et la recombinaison de la lumière paroptique intégrée. Le type d’optique intégrée étudié ici est un composant optique planaire sur lequel des guides d’ondes ont été gravés. l’optique intégrée est de type nuller et prend en entrée le flux de quatre sous-pupilles. Les guides sont agencés selon une certaine architecture permettant de réaliser dans un premier temps une fonction annulante sur trois bases puis une mesure des franges d’interférence sur les trois voies annulées. J’ai réalisé un étalonnage complet de cette optique intégrée ainsi que des mesures de clôture de phase.En conclusion, j’ai pu montrer la viabilité de l’instrument FIRST-IR avec ce nouveau concept d’optique intégrée de type nuller. En particulier j’ai démontré que la mesure de la clôture de phase reste stable pour une cible point source, quel que soit le taux d’annulation interférométrique appliqué. / The detection of exoplanets and young stars environment such as debris disks deals with two major difficulties: on one hand, the low angular distance between companion (or disk) and its host star, and on the other hand, the high contrast of flux between the two components. Interferometry is one of the techniques that solves these two issues. It is particularly the case in the application of nulling interferometry, in which we extinguish the flux from the main star thanks to coherence properties of the light.My thesis work takes part in this context, with the study of eight debris disks observationnal data made at the Very Large Telescope, using the Sparse Aperture Maskig interferometric technique. I achieved the data reduction and the analysis of closure phases. As no companion was found in the data, I derived detection limits in terms of luminosity and estimated mass.My thesis also consisted in an instrumental part, with the conception of the FIRST-IR (Fibered Imager foR a Single Telescope InfraRed) instrument in laboratory. This instrument is an interferometer which associates fibered pupil remapping technique and integrated optic based recombination of light.To conclude, I have shown the viability of FIRST-IR instrument using this new integrated optic based nuller architecture. Particularly, I demonstrated that closure phase remains stable for a source point target, regardless of the nulling level applied.

L'observation des exoplanètes pose deux problèmes : le contraste entre la planète et l'étoile et leur très faible séparation. L'une des techniques permettant de résoudre ces difficultés est l'interférométrie en frange noire : deux pupilles sont recombinés pour faire une interférence destructive sur l'étoile, et leur base est réglée pour que l'interférence soit constructive sur la planète. Cependant, pour garantir une extinction suffisante de l'étoile, la différence de trajet optique entre les faisceaux doit être de l'ordre du nanomètre, et le pointage meilleur que le centième de tache d'Airy, malgré les perturbations extérieures.Pour valider les points critiques d'une telle mission spatiale, un démonstrateur de laboratoire, PERSÉE, a été défini par un consortium dirigé par le CNES et incluant l'IAS, le LESIA, l'ONERA, l'OCA et Thales Alenia Space puis intégré à l'Observatoire de Meudon. Ce banc simule une mission spatiale dans son ensemble (interféromètre et cophasage nanométrique). Son objectif est de délivrer et maintenir une extinction de 10^-4 stabilisé à mieux que 10^-5 sur plusieurs heures, en présence de perturbations typiques que l'on injecte.Mon travail de thèse a consisté à intégrer le banc en étapes successives et à développer des procédures d'étalonnage. Ceci m'a aidé à caractériser les différents éléments critiques séparément avant de les regrouper. Après avoir mis en œuvre les boucles de contrôle du cophasage, leur analyse précise m'a permis de réduire à 0,3 nm rms le résidu de différence de marche, et à 0,4 % de la tache d'Airy le résidu de tip/tilt, malgré la présence de perturbations d'une dizaine de nanomètres d'amplitude, constituées de plusieurs dizaines de fréquences vibratoires entre 1 et 100 Hz. Cela a été possible grâce à l'implémentation d'un contrôleur linéaire quadratique gaussien, paramétré par la mesure préalable de la perturbation pour la réduire au maximum. Grâce à ces très bons résultats, j'ai pu obtenir un taux d'extinction record sur la bande [1,65 – 2,45] µm de 8,8x10^-6 stabilisé à 9x10^-7 sur quelques heures, soit une décade meilleure que les spécifications initiales. L'extrapolation de ces résultats au cas d'une mission spatiale montre que les performances attendues sont atteignables si le flux disponible est suffisamment important. Avec des télescopes de 40 cm et une fréquence d'asservissement de l'ordre de 100 Hz, des étoiles de magnitude inférieure à 9 devraient être observables. / There are two problems with the observation of exoplanets: the contrast between the planet and the star and their very low separation. One technique solving these problems is nulling interferometry: two pupils are recombined to make a destructive interference on the star, and their base is adjusted to create a constructive interference on the planet. However, to ensure a sufficient extinction of the star, the optical path difference between the beams must be around the nanometer, and the pointing must be better than one hundredth of Airy disk, despite the external disturbances.To validate the critical points of such a space mission, a laboratory demonstrator, PERSÉE, was defined by a consortium led by CNES, including IAS, LESIA, ONERA, OCA and Thales Alenia Space and integrated in Meudon Observatory. This bench simulates the entire space mission (interferometer and nanometric cophasing system). Its goal is to deliver and maintain an extinction of 10^-4 stable at better than 10^-5 over a few hours in the presence of typical injected disturbances.My thesis work consisted in integrating the bench in successive stages and to develop calibration procedures. This helped me to characterize the critical elements separately before grouping them. After having implemented the control loops of the cophasing system, their precise analysis helped me to reduce down to 0.3 nm rms the residual OPD, and 0.4 % of the Airy disk the residual tip/tilt, despite disturbances of tens of nanometers, consisting of several tens of vibrational frequencies between 1 and 100 Hz. This has been achieved by the implementation of a linear quadratic Gaussian controller, parameterized by the preliminary measurement of the disturbance to minimize. Thanks to these excellent results, I obtained on the band [1.65 – 2.45] µm a record null rate of 8.8x10^-6 stabilized at 9x10^-7 over a few hours, a decade better than the original specifications. An extrapolation of these results to the case of a space mission shows that the expected performance is achievable if the available flux is sufficiently important. With telescopes of 40 cm and a control frequency around 100 Hz, stars brighter than magnitude 9 should be observable.

Parmi les méthodes qui permettent de détecter des exoplanètes, la photométrie des transits est celle qui a connu le plus grand essor ces dernières années grâce à l’arrivée des télescopes spatiaux CoRoT (en 2006) puis Kepler (en 2009). Ces deux satellites ont permis de détecter des milliers de transits potentiellement planétaires. Étant donnés leur nombre et l’effort nécessaire à la confirmation de leur nature, il est essentiel d’effectuer, à partir des données photométriques, un classement efficace permettant d’identifier les transits les plus prometteurs et qui soit réalisable en un temps raisonnable. Pour ma thèse, j’ai développé un outil logiciel, rapide et automatisé, appelé BART (Bayesian Analysis for the Ranking of Transits) qui permet de réaliser un tel classement grâce une estimation de la probabilité que chaque transit soit de nature planétaire. Pour cela, mon outil s’appuie notamment sur le formalisme bayésien des probabilités et l’exploration de l’espace des paramètres libres par méthode de Monte Carlo avec des chaînes de Markov (mcmc).Une fois les exoplanètes détectées, l’étape suivante consiste à les caractériser. L’étude du système solaire nous a démontré, si cela était nécessaire, que l’information spectrale est un point clé pour comprendre la physique et l’histoire d’une planète. L’interférométrie annulante est une solution technologique très prometteuse qui pourrait permettre cela. Pour ma thèse, j’ai travaillé sur le banc optique Nulltimate afin d’étudier la faisabilité de certains objectifs technologiques liés à cette technique. Au-delà de la performance d’un taux d’extinction de 3,7.10^-5 en monochromatique et de 6,3.10^-4 en polychromatique dans l’infrarouge proche, ainsi qu’une stabilité de σN30 ms = 3,7.10^-5 estimée sur 1 heure, mon travail a permis d’assainir la situation en réalisant un budget d’erreur détaillé, une simulation en optique gaussienne de la transmission du banc et une refonte complète de l’informatique de commande. Tout cela m’a finalement permis d’identifier les faiblesses de Nulltimate. / From all exoplanet detection methods, transit photometry went through the quickest growth over the last few years thanks to the two space telescopes, CoRoT (in 2006) and Kepler (in 2009). These two satellites have identified thousands of potentially planetary transits. Given the number of detected transits and the effort required to demonstrate their natures, it is essential to perform, from photometric data only, a ranking allowing to efficiently identify the most promising transits within a reasonable period of time. For my thesis, I have developed a quick and automated software called bart (Bayesian Analysis for the Ranking of Transits) which realizes such a ranking thanks to the estimation of the probability regarding the planetary nature of each transit. For this purpose, I am relying on the Bayesian framework and free parameter space exploration with Markov Chain Monte Carlo (mcmc) methods.Once you have detected exoplanets, the following step is to characterise them. The study of the solar system demonstrated, if it was necessary, that the spectral information is a crucial clue for the understanding of the physics and history of a planet. Nulling interferometry is a promising solution which could make this possible. For my thesis, I worked on the optical bench Nulltimate in order to study the feasibility of certain technological requirements associated with this technique. Beyond the obtention of a nulling ratio of 3,7.10^-5 in monochromatic light and 6,3.10^-4 in polychromatic light in the near infrared, as well as a stability of σN30 ms = 3,7.10^-5 estimated on 1 hour, my work allowed to clarify the situation thanks to a detailed error budget, a simulation of the transmission based on Gaussian beam optics and a complete overhaul of the computer control system. All of this finally resulted in the identification of the weaknesses of Nulltimate.

The existence of other habitable worlds and the possible development of life elsewhere in the Universe have been among mankinds fundamental questions for thousands of years. These interrogations about our origins and place in the Universe are today at the dawn of being answered in scientific terms. The key year was 1995 with the discovery of the first extrasolar planet orbiting around a solar-type star. About 400 extrasolar planets are known today and the possibility to identify habitable worlds and even life among them largely contributes to the growing interest about their nature and properties. However, characterizing planetary systems is a very difficult task due to both the huge contrast and the small angular separation between the host stars and their environment. New techniques have emerged during the past decades with the purpose of tackling these fantastic observational challenges. In that context, infrared interferometry is a very promising technique, since it provides the required angular resolution to separate the emission of the star from that of its environment. This dissertation is devoted to the characterization of extrasolar planetary systems using the high angular resolution and dynamic range capabilities of infrared interferometric techniques. The first part of the present work is devoted to the detection with current interferometric facilities of warm dust within the first few astronomical units of massive debris discs around nearby stars. In order to extend the imaging of planetary systems to fainter discs and to extrasolar planets, we investigate in a second step the performance of future space-based nulling interferometers and make a comparison with ground-based projects. Finally, the third part of this work is dedicated to the impact of exozodiacal discs on the performance of future life-searching space missions, the goal being to characterize extrasolar planets with sizes down to that of the Earth.

The detailed nature of radio emission processes of pulsars and the exact location and distribution of the pulse emitting regions are still shrouded with mystery. Pulsars with drifting subpulses are considered as an important key for unlocking the mystery of how radio pulsars work. The phenomenon of subpulse drifting (first reported by Drake & Craft (1968)) is manifested as an organized subpulse behavior - subpulses appear at progressively changing longitude in the pulse window following some particular path. The path followed by the subpulses is specific to the individual pulsar concerned and is known as drift band. Drifting is generally characterized by Pm2(horizontal separation between the drift bands, i.e. in pulse longitude) and Pm3(vertical separation between the drift bands, i.e. in pulse numbers). The subpulse drifting phenomenon finds a natural explanation in the model of Ruderman & Sutherland (1975). According to this model, the subpulse drifting is produced from a system of sub-beams (subpulse associated plasma columns). Sparks (sparking discharges within the vacuum gap) rotating around the magnetic axis under the action of an E x B drift, give rise to a circulating pattern of sub-beams, and the time for one full circulation is referred to as the carousel rotation period, which we designate as P4. As pulsar radiation beams are widely believed to be arranged in concentric cones, it is natural to expect the circulating sparks to be distributed in annular rings on the polar cap. Each of these rings gives rise to one cone in the nested cones of emission. It has been recently shown that, subpulse drift may be fairly common among pulsars (Weltevrede et al. (2006) and (2007)). Hence, the pulsar radio emission mechanism is most likely closely connected with mechanism for drifting. In spite of significant progress both in high quality observations of drifting (e.g. Weltevrede et al. (2006) and (2007)) and attempts for confronting the results from the observations with existing models (e.g. Deshpande & Rankin (1999) and Gupta et al. (2004) etc), the pulsar emission mechanism is still an unsolved puzzle. Backer (1970b) first reported that emission from certain pulsars abruptly switches off for several periods, and suddenly comes back. This phenomenon is known as nulling. Nulling appears to be random, broadband and intrinsic to the concerned pulsar. Nulling is quite common in pulsars (Biggs, 1992). Although different aspects of the phenomenon of nulling are investigated in detail for many pulsars by several authors using high sensitivity observations, nulling is not yet explained by the existing theoretical models for pulsar radio radiation. In this thesis, I have mainly studied phenomenon of subpulse drifting and nulling, with the aim to probe the radio emission processes of pulsars. Most of the pulsars have a narrow duty cycle of emission (5-10 % of pulsar period). This is generally consistent with the expectations of the angular width of the polar cap, for typical viewing geometries. However, there are small but significant number of pulsars with unusually wide profiles where the emission is seen for a wide range of longitude (≥ 90 degrees). These are expected to be pulsars which are highly aligned, i.e. the magnetic dipole axis is almost parallel to the spin axis. In such a case, the line of sight (LOS) is very close to both the rotation and the magnetic axes, and consequently, we sample a large region of the polar cap. This has the exciting potential to allow a detailed study of the distribution and behavior of emission regions located in an annular ring around the magnetic axis. The study of pulsars showing systematic subpulse drift patterns provides important clues for the understanding of the unsolved problems of pulsar emission mechanism. Constraints provided by such observations can have far reaching implications for the theoretical models, as exemplified by some of the recent results in this area (e.g. Deshpande & Rankin (1999) and Gupta et al. (2004)). In this context, wide profile drifting pulsars can provide extra insights because of the presence of simultaneous multiple drift bands. During the thesis period, I have mainly concentrated on the study of single pulse properties of two wide profile drifting pulsars, PSR B0818-41 and PSR B0826-34. In depth study of PSR B0818-41 We have studied single pulse properties of a relatively less studied wide profile pulsar, B0818-41 using highly sensitive multi-frequency observations with the GMRT in full polar mode. Detailed investigation of PSR B0818-41 are reported in Chapters 2, 3 and 4 of this thesis. New results from our study are described in the following. We estimate the mean flux of PSR B0818-41 at 5 different frequencies and show that the spectrum flattens at frequencies lower than 325 MHz (at 244 or 157 MHz), providing indication of a low frequency turn-over. Significant linear polarization is observed at 325, 610 and 1060 MHz. Average linear polarization falls off much faster than the total intensity and decreases to zero near the outer edge of the profile. This can be explained by the orthogonal polarization mode jump at the edges of the profile observed at 325 MHz. Polarization angle sweep across the pulse profile evolves remarkably with frequency (between 325, 610 and 1060 MHz), which is not generally observed in other pulsars. Very less circular polarization without any signature of changing handedness is observed at 325 and 610 MHz. But circular polarization changes sign at the middle of the pulse profile at 1060 MHz. We report the discovery of a remarkable subpulse drift pattern in PSR B0818-41, using the high sensitivity GMRT observations. We find simultaneous occurrence of three drift regions with two different drift rates: an inner region with steeper apparent drift rate flanked on each side by a region of slower apparent drift rate. The closely spaced drift bands always maintain a constant phase relationship: the subpulse emission from the inner drift region is in phase with that from the outer drift region on the right hand side, and at the same time the emission in the inner drift region is out of phase with the outer drift region situated on the left hand side. This phase locked relationship (hereafter PLR) is maintained for the entire stretch of the data (for all the epochs of observations at 325 and 610 MHz) and does not appear to get perturbed after intermittent nulling or during changes in the drift rate. We observe frequent changes of drift rates. We see extreme examples of changing drift rates such as transitions from negative to stationary or stationary to negative drift rates, many of which appear to have some connection with nulls. We investigate changes in drift rates for about 10,000 pulses from two different epochs of observations at 325 MHz and observe frequent occurrences of small changes in the drift rate, seven transitions from negative to stationary drift rates, five transitions from stationary to negative drift rates, and two possible signatures of curved drift bands. In addition to the remarkable subpulse drift observed at 325 MHz, we report subpulse drifting at 244 and 610 MHz. At 244 MHz subpulse drifting is observed only in the leading and trailing outer regions, but not in the inner region. Though the drift bands are weaker, subpulse drifting is observed in both inner and outer region at 610 MHz. Pm2, Pm3 and ΔΦs(subpulse width) are determined for the inner and the outer drift regions for different frequencies. Though Pm3 is observed to be the same for the inner and outer drift regions, pm2 and ΔΦsare different for different drift regions. The unique drift pattern of this pulsar can be naturally explained as being created by the intersection of our LOS with two conal rings on the polar cap of a fairly aligned rotator. Based on the frequency evolution of the average profile, observed polarization angle (PA) swing and results from subpulse drifting, we converged on two possible choices of emission geometry: G-1 (inclination angle α= 11 deg and impact angle β= -5.4 deg; which incidentally reproduces the middle part of the PA sweep at 610 MHz) and G-2 (α=175.4 deg and β=- 6.9 deg; geometry derived from RVM fit to 325 MHz PA sweep). Pulsar radiation pattern simulated with both the geometries reproduces the average profile as well as the observed features in the drift pattern quite well. However, G-2 fits the PA sweep much better. We report that the peaks of the emission from the trailing and leading outer regions, as a function of the pulse number, are offset by a constant interval, P5~9P1. We also report a phase locked relation (PLR) between the inner and outer drift regions for PSR B0818-41. A new technique is introduced by us for resolving aliasing, using this constant offset (P5 ~ 9P1) between the peak emission from the leading and trailing outer regions. From the result of this technique, we propose that the subpulse drifting for PSR B0818 -41 is most likely first order aliased, and the corresponding carousel rotation period 4 =10 s. This implies that PSR B0818 -41 has the fastest known carousel. The drift pattern in the inner and outer rings are always phase locked for PSR B0818 -41. This could be a significant constraint for the theoretical models of pulsar radio emission, and favors a pan magnetospheric emission mechanism. We observe frequent nulling for PSR B0818-41. We calculate a nulling fraction ~30% at 325 MHz for this pulsar. Lengths of neighboring nulls and bursts are found to be independent. For the inner drift region, our investigations bring out the fact that the nature of the transitions from burst to null are different from the transitions from null to burst. Switching off of pulsar radiation during nulling for PSR B0818 -41 is not abrupt, but is gradual, whereas the transitions from null to burst are found to be rather abrupt for the inner drift region. This effect is not prominent in the outer drift regions. Although, the inner region of the last active pulses before nulls are dimmer, the first active pulses after nulls outshines the normal ones. The intensity of the inner region is maximum for the average profile from the first active pulse immediately after the nulls and then gradually goes down. This is consistent with the behavior of the individual nulls described above. However, this is not the case for the leading and trailing outer regions. The average profiles from the first active pulse immediately after the nulls follows similar shape as the normal profile but shows an increased intensity (in the form of a bump) in the inner region which is not present in the normal average profile. In addition, the leading and the trailing peaks appear to be of similar intensity, while trailing peak is significantly more intense for the normal profile. The average profiles from the pulses immediately after the nulls are wider than the normal profile. The average profiles of the first active pulses after the nulls are drastically similar between two epochs of observations. This is a very unique result which is not reported for any other pulsar so far and may imply that the phenomenon of nulling is associated with some systematic energy re-distribution in the pulsar magnetosphere. In depth study of PSR B0826-34 PSR B0826-34 is a pulsar with one of the widest known profile. The earlier studies of this pulsar (Durdin et al. (1979), Biggs et al. (1985) and Gupta et al. (2004)) have brought out some unique properties : strong evolution of the average profile with frequency, apparent nulling for 70% of time and a remarkable subpulse drift property- multiple curved drift bands with frequent changes and sign reversals of drift rate. We studied PSR B0826 -34 using the GMRT, simultaneously at 303 and 610 MHz, and individually at 157, 325, 610 and 1060 MHz. Detailed investigation of PSR B0826- 34 are reported in Chapter 5 of this thesis. Some of the interesting new results from our work are, As a natural out-come of the simultaneous dual frequency observations, we obtain an accurate DM value, equal to 52.2(6) pc/cm3, for this pulsar. Unlike most normal pulsars the DM determination for this pulsar is a difficult and trick exercise, mainly because the profile is quite complex, very wide and strongly evolving with frequency. The advantage of our method of DM determination is that the observations at a single epoch are self sufficient for obtaining the DM value at that epoch. Contrary to the earlier study by Esamdin et al. (2005), we find no evidence of weak emission during the typical long null states of this pulsar, simultaneously at 303 and 610 MHz, as well as from non simultaneous observations at 157, 325, 610 and 1060 MHz at separate epochs. We have also obtained absolute flux limits for the non-detection at various frequencies, which should be a useful comparison standard for any more sensitive studies in the future. We present the average profiles at five different frequencies. Main pulse (MP) and inter pulse (IP) emission observed for this pulsar span over wide pulse longitude. There is a remarkable frequency-evolution of pulse profile: IP becomes stronger with increasing frequency. We estimated the mean flux of the MP, IP and the full pulse region of PSR B0826- 34 at different frequencies of observation. Significant correlation in the total intensity of the individual pulses between 303 and 610 MHz is reported from the simultaneous dual frequency observations, which is indicative of the broad-band nature of the emission. The intensity correlations are positive for large lags, indicating that there is some kind of memory in the underlying structure. This memory is the longest for PSR B0826- 34, amongst all known cases. Our study of this pulsar brings out insight into simultaneous behavior of the single pulses from PSR B0826- 34 at 303 and 610 MHz, which has not been examined so far. We see about 6 -7 drift bands in the MP region at 303 and at 610 MHz. At 610 MHz we see about 2 -3 drift bands in the IP region. We observe wide variations in the drift rates, including positive and negative drift rates and curved drift bands, which are simultaneous for both frequencies. We have noticed coherence between simultaneous multiple drift bands - at some given instant of time all the drift bands (6 -7 drift bands) under the MP window show similar kind of drift. Though we find the drift pattern to be very similar in the simultaneous 303 and 610 MHz data, we observe that the drift band separation (Pm2) evolves significantly between these two frequencies, and in a manner opposite to the average profile evolution. In addition, we confirm the dependence of Pm2 on pulse longitude at 303 MHz and find indications for the same at 610 MHz. Significant linear polarization is observed in the MP region which drops abruptly at the edges of the pulse profile. Two orthogonal mode jumps are seen at the edges of the MP for both 325 and 610 MHz. We observe somewhat non orthogonal mode jump at the edges of IP for 610 MHz. Significant circular polarization in the MP along with the sense reversal near the center is observed for both the frequencies. The PA curve shows typical ”S” shaped swing (though there is some hint of a kink in the central part of the PA curve). RVM fit (Radhakrishnan & Cooke, 1969) to the PA curve is obtained with α~ 9.8 deg, β~3.2 deg, at both 325 and 610 MHz. The detailed study of two unique wide profile pulsars, PSR B0818-41 and PSR B0826 -34, was very rewarding and provided fair amount of insight towards the emission properties of pulsars. We broadly conclude that the emission from simultaneous multiple drift bands are coherent. In other words the emission mechanism responsible for generation of the drift bands is heavily correlated in the whole on pulse window. Also the equispaced sparks argues for a more isotropic arrangement of sparks which is favored by the conal model (Rankin, 1983). Drifting from more than one rings are observed only for two pulsars, PSR B0818-41 and PSR B0826-34. For PSR B081841 we observe that the emission from different rings are always locked in phase. This constant phase relation is maintained even during sequences of irregular drifting as well as after nulling. PSR B0826 -34 is another wide profile pulsar for which presence of simultaneous multiple drift regions are observed. For this pulsar the MP and the IP emission are interpreted to be coming from two concentric rings of emission. The drift bands in these regions are locked in phase implying that the emission from the inner and the outer rings are in phase. For PSR B0826- 34 we observe frequent nulling and changes of drift rates which are simultaneous for both the inner and outer rings. Hence for all pulsars for which we know drifting from more than one ring, the drift pattern in the inner and outer rings are always phase locked. No counter example is observed. This requires common drift rate in the inner and outer rings, implying that emission in the two rings are not independent, and the conditions responsible for drifting are similar in both rings. Our finding of PLR between the emission from the inner and the outer rings puts constraints on the theoretical models of pulsar emission mechanism and favors a pan magnetospeheric radiation mechanism. Preliminary study of single pulse properties of six other pulsars Inspired by the success of our study of PSR B0818- 41 and PSR B0826-34 we carried out single pulse study of few other pulsars with diverse profile. Preliminary results from this study are presented in Chapter 6. However, some of the new results form this work are highlighted in the following. We report occasional nulling for PSR B0540+23 which is important in the sense that nulls are not commonly seen in the core components. We observe simultaneous two drift bands for B1819- 22 at 325 and 610 MHz. We observe some kind of mode changing between stronger and weaker modes with changes of drift rates, which are probably associated with occasional nulling observed in this pulsar. For PSR B1839 -04 subpulse drifting is observed under the two peaks of the profile. The emission under the leading and trailing peaks appear to be in phase. Determination of the orbital parameters of binary pulsars Apart from the above work, I got interested in determination of the orbital parameters of the binary pulsars. This work was triggered by the discovery of a binary pulsar PSR J0514- 4002 (the first known pulsar in the globular cluster NGC 1851) at the GMRT in 2004 (Freire et al., 2004). We present a novel method for determination of the orbital parameters of binary pulsars, using data on the pulsar period at multiple observing epochs in contrast to the method described by Freire, Kramer & Lyne (2001) which requires both pulsar period and period derivatives at particular observing epochs. This method uses the circular nature of the velocity space orbit of Keplerian motion and produces preliminary values based on two one dimensional searches. Preliminary orbital parameter values are then refined using a computationally efficient linear least square fit. This method works for random and sparse sampling of the binary orbit. Unlike the method used by Freire, Kramer & Lyne (2001), which works for nearly circular binary orbits, this method works for binary orbit with any eccentricity. We demonstrate the technique on (a) the highly eccentric binary pulsar PSR J0514- 4002 (the first known pulsar in the globular cluster NGC 1851) and (b) 47 Tuc T, a binary pulsar with a nearly circular orbit. Our result agrees with the earlier determination of the orbital parameters of the binary pulsars done with coherent multi-epoch timing (Freire, Kramer & Lyne (2001) and Freire et al. (2007)). In our method the computation involves only one dimensional searches and linear least square fits. This study is reported in Chapter 7. The main conclusions and the possible future works are presented in Chapter 8.