Chapter 1 of this thesis details the incorporation of a Charged Coupled Device (CCD) detector system with the Durham Imaging Polarimeter. The details include the physical characteristics of the device and the electronics and software associated with the device control and data storage. The introduction of the CCD detector system haa made necessary the inclusion of a super-achromatic half-wave plate in the polarimeter which has an inherent variability in its optic axis. Chapter 2of this work describes fully how suitable corrections for this effect can be made, and derives "first order" results. The CCD performance is examined in comparison with the detector used previously and hence the veracity of the new results is established. Chapter 3 is a relevant summary of the status of the astronomy of the immediate regions of recent star-formation. Chapter 4 describes multicolour polarimetry of NGC2261/R Mon covering the period 1979 to 1986. The data conclusively proves that the polarisation of R Mon must be due to effects close to R Mon (~ 14 astronomical units). This is evident because of the dynamic timescale of the variations of the polarisation of R Mon and the anomalous band of polarisations seen across the head of the nebula. The interpretation presented is an extension of the Elsasser and Staude (1978) method of polarising objects embedded within the confines of a nearly edge-on disk. Detailed polarisations within the main nebula body provide evidence for this extended interpretation and also for an extensive helical magnetic field which may extend into the disk. Also it is seen that R Mon must still be "shrouded" in material preventing light from directly reflecting in the main nebula body. It is not thought that the variations in the region close to R Mon are due to planetary bodies but to accretion from the disk. The results of this re-interpretation of the polarising mechanism are tentatively applied to other similar objects.

We use Integral Field Unit (IFU) data for a subset of galaxies in the MaNGA (Mapping Nearby Galaxies at Apache Point Observatory) sample to investigate the environmental dependence of H-alpha properties for nearby star-forming galaxies. We characterize the non-AGN H-alpha emission for galaxies living in different host environments with radial gradient measurements, half-light radii, as well as measures of concentration and asymmetry. We find that global specific star formation rates (sSFR) are lower in nearby star-forming galaxies in groups and clusters compared to those in the field, and the lowest in high density environments such as group or cluster centres. From the resolved data we find that the overall reduction in H-alpha emission in star-forming galaxies in denser environments occurs across the face of these galaxies, suggesting starvation as a primary quenching mechanism. We further find that H-alpha disks are truncated in group galaxies that live nearer the center of the halo compared to those in the outer halo or field, which may be due to ram pressure stripping in these dense environments. / Thesis / Master of Science (MSc) / In order to understand the evolution of galaxies over time, it is necessary to determine the relative importance of external and internal factors that affect galaxy star formation. We know that galaxies in dense environments have less star formation (are quenched) compared to galaxies in the field. However, the mechanisms that dominate this quenching are less well constrained. We use a sample of galaxies in the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey to investigate the dependence of star formation on other galaxy properties as well as properties of the host environment. We find that galaxies have reduced H-alpha emission, a signature of star formation, across the entire face of the galaxy in groups and clusters compared to galaxies in the field. We further find that galaxies nearer the centre of the group or cluster halo have truncated H-alpha disks compared to galaxies in the outer part of the halo or in the field.

The interstellar matter in the Galaxy is concentrated in a thin layer close to the galactic plane, mostly in spiral arms. Most of the interstellar matter is in a form of atomic and molecular gas and only 1% of its mass is in a form of small (0.01 – 0.1 µm) dust grains which absorb and scatter the light of stars and cause the interstellar extinction. A part of interstellar gas and dust are in a diffuse form and fill the space with density which exponentially decreases with the distance from the galactic plane. However, in the spiral arms gigantic molecular clouds are present which play an outstanding role in the evolution of the Galaxy, since in them star forming processes take place. Molecular and dust clouds, young star clusters and associations and other star forming regions are concentrated in the Milky Way plane. However, due to gravitational and radiation interactions between the molecular clouds and the young massive stars, some fragments of spiral arms deviate from the galactic plane. One of such deviating branches from the Local (Orion) spiral arm is a huge elongated system of molecular and dust clouds located in the Cepheus constellation which is known as the Cepheus Flare. Most of the objects investigated in this dissertation belong to this branch of the Local spiral arm. The objects selected for the investigation are star forming regions in the vicinity of the reflection nebula NGC 7023, a group of dark clouds TGU 619, the young open cluster NGC 7129 and the... [to full text] / Paukščių tako Galaktikoje didžioji dalis tarpžvaigždinės medžiagos yra susitelkusi į ploną sluoksnį Galaktikos plokštumoje, daugiausiai spiralinėse vijose. Didžiąją dalį tarpžvaigždinės medžiagos sudaro atominės ir molekulinės dujos ir tik maždaug 1% masės yra mažos (0.01 – 0.1 µm) dydžio dulkelės, kurios sugeria ir išsklaido šviesą ir sukelia tarpžvaigždinės ekstinkcijos reiškinį. Spiralinėse vijose esantys molekuliniai debesys yra svarbūs Galaktikos evoliucijos procese, nes juose vyksta aktyvūs žvaigždžių formavimosi procesai. Molekuliniai ir dulkių debesys, jaunų žvaigždžių spiečiai ir asociacijos bei kitos žvaigždžių susidarymo sritys dažniausiai yra Galaktikos plokštumoje. Tačiau dėl gravitacinės ir radiacinės sąveikos tarp jaunų didelės masės žvaigždžių ir molekulinių debesų kai kuriose Paukščių Tako srityse žvaigždėdaros rajonai nukrypsta nuo Galaktikos plokštumos. Viename iš tokių rajonų Cefėjo žvaigždyno kryptimi dalis tarpžvaigždinių debesų ir žvaigždėdaros rajonų yra nukrypę nuo Galaktikos plokštumos link šiaurinio dangaus poliaus ir sudaro Paukščių Tako atšaką, literatūroje žinomą kaip Cepheus Flare. Dauguma šioje disertacijoje tyrinėjamų objektų priklauso šiai Cefėjo atšakai. Šio darbo tikslas yra Cefėjo žvaigždėdaros rajonų, žinomų kaip atspindžio ūkas NGC 7023, tamsiųjų debesų kompleksas TGU 619 ir jaunas spiečius NGC 7129 fotometrinis tyrimas, siekiant nustatyti šių objektų nuotolį ir tarpžvaigždinę ekstinkciją, jauno spiečiaus NGC 7129 ir... [toliau žr. visą tekstą]

Paukščių Tako Galaktikoje didžioji dalis tarpžvaigždinės medžiagos yra susitelkusi į ploną sluoksnį Galaktikos plokštumoje, daugiausiai spiralinėse vijose. Didžiąją dalį tarpžvaigždinės medžiagos sudaro atominės ir molekulinės dujos ir tik maždaug 1% masės yra mažos (0.01 – 0.1 µm) dydžio dulkelės, kurios sugeria ir išsklaido šviesą ir sukelia tarpžvaigždinės ekstinkcijos reiškinį. Spiralinėse vijose esantys molekuliniai debesys yra svarbūs Galaktikos evoliucijos procese, nes juose vyksta aktyvūs žvaigždžių formavimosi procesai. Molekuliniai ir dulkių debesys, jaunų žvaigždžių spiečiai ir asociacijos bei kitos žvaigždžių susidarymo sritys dažniausiai yra Galaktikos plokštumoje. Tačiau dėl gravitacinės ir radiacinės sąveikos tarp jaunų didelės masės žvaigždžių ir molekulinių debesų kai kuriose Paukščių Tako srityse žvaigždėdaros rajonai nukrypsta nuo Galaktikos plokštumos. Viename iš tokių rajonų Cefėjo žvaigždyno kryptimi dalis tarpžvaigždinių debesų ir žvaigždėdaros rajonų yra nukrypę nuo Galaktikos plokštumos link šiaurinio dangaus poliaus ir sudaro Paukščių Tako atšaką, literatūroje žinomą kaip Cepheus Flare. Dauguma šioje disertacijoje tyrinėjamų objektų priklauso šiai Cefėjo atšakai. Šio darbo tikslas yra Cefėjo žvaigždėdaros rajonų, žinomų kaip atspindžio ūkas NGC 7023, tamsiųjų debesų kompleksas TGU 619 ir jaunas spiečius NGC 7129 fotometrinis tyrimas, siekiant nustatyti šių objektų nuotolį ir tarpžvaigždinę ekstinkciją, jauno spiečiaus NGC 7129 ir... [toliau žr. visą tekstą] / The interstellar matter in the Galaxy is concentrated in a thin layer close to the galactic plane, mostly in spiral arms. Most of the interstellar matter is in a form of atomic and molecular gas and only 1% of its mass is in a form of small (0.01 – 0.1 µm) dust grains which absorb and scatter the light of stars and cause the interstellar extinction. A part of interstellar gas and dust are in a diffuse form and fill the space with density which exponentially decreases with the distance from the galactic plane. However, in the spiral arms gigantic molecular clouds are present which play an outstanding role in the evolution of the Galaxy, since in them star forming processes take place. Molecular and dust clouds, young star clusters and associations and other star forming regions are concentrated in the Milky Way plane. However, due to gravitational and radiation interactions between the molecular clouds and the young massive stars, some fragments of spiral arms deviate from the galactic plane. One of such deviating branches from the Local (Orion) spiral arm is a huge elongated system of molecular and dust clouds located in the Cepheus constellation which is known as the Cepheus Flare. Most of the objects investigated in this dissertation belong to this branch of the Local spiral arm. The objects selected for the investigation are star forming regions in the vicinity of the reflection nebula NGC 7023, a group of dark clouds TGU 619, the young open cluster NGC 7129 and the... [to full text]

Voilà plus d'un siècle que Victor Hess a montré l'origine cosmique de ce mystérieux rayonnement ionisant, et pourtant ce dernier n'a pas fini de livrer tous ces secrets. En deçà d'une énergie de l'ordre du PeV, les vestiges de supernovae sont les candidats les plus sérieux pour rendre compte de l'accélération de ces particules cosmiques. Si toutefois cette hypothèse demeure toujours d'actualité, alors qu'auparavant on le considérait comme un événement isolé dans la Galaxie, on constate plutôt aujourd'hui que ces explosions d'étoiles massives surviennent majoritairement au sein de grandes structures galactiques nommées superbulles. Ces objets sont formés par la combinaison des forts vents stellaires issus des étoiles massives ainsi que de plusieurs supernovae, tout ceci regroupé dans un espace de quelques dizaines ou centaines de parsecs.On peut dès lors se poser la question suivante : est-il possible que des amas d'étoiles jeunes, n'ayant pas encore connu d'épisode de supernova, puissent être des accélérateurs cosmiques.Pour ce type d'investigation, l'astronomie gamma est aux premières loges puisque contrairement au rayonnement cosmique chargé, ce type de messager céleste n'est pas dévié dans son voyage depuis la source jusqu'à nous.L'objet de ce travail est ainsi d'évaluer la possibilité pour ces amas d'étoiles jeunes, de recycler une partie de l'énergie mécanique transférée au milieu interstellaire dans l'accélération de particules et partant, dans l'émission d'un rayonnement non-thermique. Cette étude propose, à partir d'un spectre d'injection pour des particules chargées (proton et/ou électrons), de modéliser l'émission non-thermique attendue considérant les pertes que celles-ci subissent. Un catalogue d'amas potentiellement prometteurs est dressé ainsi qu'un classement de ceux-ci au regard du flux de gamma attendu. Une analyse des données des télescopes H.E.S.S. est conduite pour un certain nombre d'amas sélectionnés. Ce réseau de télescopes Cherenkov situé en Namibie est le plus performant dans sa catégorie. Il est dédié à l'observation des rayons gamma de très haute énergie.Une analyse des données du Fermi-LAT ont également été effectuées. Il s'agit cette fois d'un satellite dédié à la partie des hautes énergies du rayonnement gamma.Enfin, on contraint les paramètres de notre modèle grâce aux résultats issus de ces analyses.L'expérience H.E.S.S., qui a fonctionné à 4 télescopes dès 2003, est depuis 2012 au tout début de sa deuxième phase consistant en l'ajout d'un cinquième télescope de plus grand diamètre. On montre ici, grâce à des simulations de gerbes, la nécessité pour ce télescope de disposer d'un système de focus permettant l'ajustement de la distance caméra-miroirs conduisant à de meilleures performances (taux de déclenchement, résolution angulaire). / More than one century ago, Victor Hess discovered the cosmical origin of the mysterious ionizing radiation. Yet, nowadays it still has a lot of secrets for us. Roughly below the PeV energy, the best candidates already proposed in 1934 were the supernovae remnants (SNR). These candidates still remain ; in the past we considered isolated SNRs, while today we rather think about SNRs inside big structures as superbubbles. These objects are formed by powerful stellar winds from massive stars combined with several SNRs gathered in a space of some decades or hundreds of parsecs. Observations show that the majority of the SNRs occurs in such regions. The point for us is to know if star clusters or associations of massive stars, not hosting any SNR, could also accelerate particles to very high energies and consequently emit gamma-rays.The gamma-ray astronomy is relevant in order to solve this type of riddle because the Very High Energy photons do not suffer of any deviation due to the Galactic magnetic field. It means that we can get informations from the source itself by detecting the gamma-ray radiation.In our study we assume that a part of the mechanical energy transferred to the interstellar medium can be used to accelerate charged particles, which will emit non-thermal radiations.First we assume a given injection spectrum (for electrons and/or protons), then we model the non-thermal emission expected considering particles losses.We deliver a catalogue of promising clusters and we rank them according to the expected strength of the gamma-ray flux.We conducted the analysis of H.E.S.S. data collected toward some selected clusters. The H.E.S.S. experiment is situated in Namibia and is the most efficient array of Cherenkov telescopes. We also used the Fermi-LAT public data. Fermi is a space-based telescope for High Energy gamma ray.Then we constrain our model with the obtained analysis results.The H.E.S.S. experiment had initially 4 telescopes in operation since 2003. In 2012, the second phase of the experiment started when a fifth larger one was added. We show here that it is relevant for this telescope to use a focus system in order to move the camera and change the distance camera-mirrors. The simulations show that the focus system leads to better performances (trigger rate, angular resolution).

L'ère des observations interférométriques mène à la nécessité d'une description plus précise de la structure physique et de la dynamique des régions de formation d'étoiles, des coeurs pré-stellaires et des disques proto-planétaires. L'émission moléculaire et du continuum de la poussière peuvent être décrites par de multiples composantes physiques. Pour comparer avec les observations, un modèle de transfert radiatif précis et complexe de ces régions est nécessaire. J'ai développé au cours de cette thèse une application autonome appelée GASS (Generator of Astrophysical Sources Structures, Quénard et al., soumis) à cette fin. Grâce à son interface, GASS permet de créer, de manipuler et de mélanger différents composants physiques tels que des sources sphériques, des disques et des outflows. Dans cette thèse, j'ai utilisé GASS pour travailler sur différents cas astrophysiques et, entre autres, j'ai étudié en détail l'eau et l'émission de l'eau deutérée dans le coeur pré-stellaire L1544 (Quénard et al., 2016) ainsi que l'émission des ions dans la proto-étoile de faible masse IRAS16293-2422 (Quénard et al., soumis). / The era of interferometric observations leads to the need of a more and more precise description of physical structure and dynamics of star-forming regions, from pre-stellar cores to proto-planetary disks. The molecular and dust continuum emission can be described with multiple physical components. To compare with the observations, a precise and complex radiative transfer modelling of these regions is required. I have developed during this thesis a standalone application called GASS (Generator of Astrophysical Sources Structures, Quénard et al., submitted) for this purpose. Thanks to its interface, GASS allows to create, manipulate, and mix several different physical components such as spherical sources, disks, and outflows. In this thesis, I used GASS to work on different astrophysical cases and, among them, I studied in details the water and deuterated water emission in the pre-stellar core L1544 (Quénard et al., 2016) and the emission of ions in the low-mass proto-star IRAS16293-2422 (Quénard et al., submitted).

No description available.