• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 31
  • 6
  • 1
  • 1
  • Tagged with
  • 51
  • 51
  • 25
  • 11
  • 11
  • 8
  • 7
  • 4
  • 4
  • 4
  • 3
  • 3
  • 3
  • 3
  • 3
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
41

Photometric analysis of R Coronae Borealis stars in the Magellanic Clouds : a thesis submitted in partial fulfilment of the requirements for the degree of Master of Science in Astronomy, Department of Physics and Astronomy, University of Canterbury /

Woollands, Robyn Michèle. January 2008 (has links)
Thesis (M. Sc.)--University of Canterbury, 2008. / Typescript (photocopy). Includes bibliographical references (p. 157-165). Also available via the World Wide Web.
42

Ensemble characteristics of the ZZ Ceti stars

Mukadam, Anjum Shagufta, Winget, Donald Earl, January 2004 (has links) (PDF)
Thesis (Ph. D.)--University of Texas at Austin, 2004. / Supervisor: D.E. Winget. Vita. Includes bibliographical references. Also available from UMI.
43

R Coronae Borealis stars : characteristics of their decline phase : a thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Astronomy in the University of Canterbury /

Skuljan, Ljiljana. January 2001 (has links)
Thesis (Ph. D.)--University of Canterbury, 2001. / Typescript (photocopy). Includes bibliographical references (p. [215]-225). Also available via the World Wide Web.
44

Galactic microlensing : binary-lens light curve morphologies and results from the Rosetta spacecraft bulge survey

Liebig, Christine Elisabeth January 2014 (has links)
For 20 years now, gravitational microlensing observations towards the Galactic bulge have provided us with a wealth of information about the stellar and planetary content of our Galaxy, which is inaccessible via other current methods. This thesis summarises work on two research topics that arose in the context of exoplanetary microlensing, but we take a step back and consider ways of increasing our understanding of more fundamental phenomena: firstly, stellar microlenses in our Galaxy that were stereoscopically observed and, secondly, the morphological variety of binary-lens light curves. In autumn 2008, the ESA Rosetta spacecraft surveyed the Galactic bulge for microlensing events. With a baseline of ∼1.6 AU between the spacecraft and ground observations, significant parallax effects can be expected. We develop a photometry pipeline to deal with a severely undersampled point spread function in the crowded fields of the Galactic bulge, making use of complementary ground observations. Comparison of Rosetta and OGLE light curves provides the microlens parallax π[subscript{E}] , which constrains the mass and distance of the observed lenses. The lens mass could be fully determined if future proper motion measurements were obtained, whereas the lens distance additionally requires the determination of the source distance. In the second project, we present a detailed study of microlensing light curve morphologies. We provide a complete morphological classification for the case of the equal-mass binary lens, which makes use of the realisation that any microlensing peak can be categorised as one of only four types: cusp-grazing, cusp-crossing, fold-crossing or fold-grazing. As a means for this classification, we develop a caustic feature notation, which can be universally applied to binary lens caustics. Ultimately, this study aims to refine light curve modelling approaches by providing an optimal choice of initial parameter sets, while ensuring complete coverage of the relevant parameter space.
45

An interactive digital image processing system

Fawcett, George January 1975 (has links)
Thesis. 1975. B.S.--Massachusetts Institute of Technology. Dept. of Electrical Engineering and Computer Science. / Includes bibliographical references. / by George Fawcett, Jr. / B.S.
46

Spectral characterization of the Herschel SPIRE photometer

Spencer, Locke Dean, University of Lethbridge. Faculty of Arts and Science January 2005 (has links)
The European Space Agency's Herschel Space Observatory is comprised of three cryogenically cooled instruments commissioned to explore the far infrared/submillimetre universe. The Spectral and Photometric Imaging REceiver (SPIRE) is one of Herschel's instruments and consists of a three band imaging photometer and a two band imaging spectrometer. Canada is involved in the SPIRE project through provision of instrument development hardware and software, mission flight software, and support personnel. This thesis discusses Fourier transform spectroscopy (FTS) and FTS data processing. A detailed discussion is included on FTS phase correction, with results presented from the optimization of an enhanced Forman phase correction routine developed for this work. This thesis discusses the design, verification, and use of the hardware and software provided by Dr. Naylor's group as it relates to SPIRE verification testing. Results of the photometer characterization are presented. The current status of SPIRE and its future schedule is also discussed. / xvii, 239 leaves : ill. (some col.) ; 28 cm.
47

Galactic star clusters in the u'g'r'i'z' photometric system

Clem, James Lewis 16 December 2009 (has links)
Although the Sloan Digital Sky Survey (SDSS) has compiled an unprecedented amount of photometric data on stellar populations in the Milky Way, it is not presently possible to accurately and consistently interpret these data due to the lack of precise fiducial stellar sequences and color-temperature relations for the new 'u'g'r'i'z' photo-metric system. In order to address these deficiencies, this study describes an extensive observational project that has obtained high-quality and homogeneous photometry for a number of different Galactic star clusters spanning a wide range in meta.llicity (-2.5 ≤ [Fe/H] ≤ +0.3), as observed in the u'g'r'i'z' passbands with the MegaCam wide-field imager on the Canada-France-Hawaii Telescope. By employing these purest of stellar populations, fiducial sequences have been defined from color-magnitude diagrams (CMDs) that. extend from the tip of the RGB down to approximately 4 magnitudes below the turnoff points: these have been accurately calibrated to the standard u'g'r'i'z` system via a set of secondary photometric standards located within these same clusters. Consequently, they can serve as a valuable set of empirical fiducials for the interpretation of stellar populations data in the system, as well as calibrators for the transformation of stellar isochrones to the u'g'r'i'z' bandpasses. In fact. when a new grid of theoretical color-Teff relations and bolometric corrections for the system is computed from Kurucz model atmospheres and employed to translate isochrones to the observed planes, generally very good and consistent fits to the CMDs of the metal-poor ([Fe/H] <0.0) globular clusters M 92, M 13, and M 71 are found, once reasonable estimates of the cluster parameters are assumed (the only obvious discrepancy is a shift of ~ 0.01 - 0.03 mag between the predicted and observed giant branches when the models are fitted to the main sequences). More-over, the same isochrone fits are entirely consistent with those inferred from cluster observations in other photometric systems - notably, the BV(RI) , and uvby systems. At the metal-rich end ([Fe/H] ≥ 0.0), however. these transformations fail to match the observed loci of cool, main-sequence stars (Teff ≤ 5000K) in the open clusters M 67 and NGC 6791. An exploration into possible causes of these discrepancies is provided.
48

Surface brightness distributions of late-type stars

Jeffers, Sandra Victoria January 2005 (has links)
The aim of this work has been to increase our understanding of the surface brightness distributions of late-type stars through Doppler imaging and eclipse mapping techniques. Combining spectroscopic and photometric observations with the technique of Doppler Imaging, I have reconstructed surface images of the G2V star He 699 (for 08 October 2000), which show high latitude and polar structures. In the case of the KOV star AB Dor, the Doppler images for January 1992 and November 1993 show a large polar cap with small dark features also present at intermediate to high latitudes. As the phase sampling of the observations was insufficient to apply the sheared-image method it was not possible to detect any differential rotation. In the second part of my thesis I determine the surface brightness distribution of the primary component of the RS CVn eclipsing binary SV Cam. I have used extrapolated size distributions of sunspots to an active star to synthesize images of stellar photospheres with high spot filling factors. The resulting surface images, reconstructed with the Maximum Entropy eclipse mapping technique, show large spurious spot features at the quadrature points. It is concluded that two-spot modelling or chi-squared minimisation techniques are more susceptible to spurious structures being generated by systematic errors, arising from incorrect assumptions about photospheric surface brightness, than simple Fourier analysis of the light-curves. Spectrophotometric data from 9 HST orbits, observed in November 2001, have been used to eclipse-map the primary component of SV Cam. In combination with its HIPPAR- COS parallax it is found that the surface flux in the eclipsed low-latitude region is about 30% lower than computed from the best fitting PHOENIX model atmosphere. This flux deficit can only be accounted for if about a third of the primary's surface is covered with unresolved spots. However, when the spottedness from the eclipsed region is applied to the entire surface of the primary star, there still remains an unaccounted flux deficit. The remaining flux deficit is explained by the presence of a large polar spot extending down to latitude 48+/-6 deg. When the Maximum Entropy eclipse mapping technique is used to fit SV Cam's lightcurve, the observed minus computed residuals show strong spurious peaks at the quadrature points. It is only possible to reduce these peaks with the addition of a polar cap and the reduction of the primary star's temperature, to account for the star being peppered with unresolvable spots. Motivated by this result we investigate the limb darkening of the primary component of SV Cam. The wavelength dependence of the limb darkening is analysed by sub-dividing the HST lightcurve into 10 bands of equal emission flux. Flux variations between the first and fourth contact of the primary eclipse indicate that the limb darkening decreases towards longer wavelengths, in accordance with published limb darkening laws. Comparing fits of ATLAS and PHOENIX model atmospheres we find a wavelength dependence of the best fitting model. Due to its smooth cutoff at the stellar limb, the spherical geometry of the PHOENIX model atmosphere gives the best fit during partial eclipse. Between the second and third contact the difference between spherical and plane-parallel geometry is less important.
49

Supermassive black holes : the local supermassive black hole mass function

Vika, Marina January 2012 (has links)
Over recent years there has been an increase of the number of secure supermassive black hole (SMBH) detections. These SMBH measurements have lead astronomers to establish well defined empirical relationships between the SMBH mass and some of the properties of the host galaxy. The number of galaxies with SMBH mass measurements is currently limited to about 100. One approach of expanding the study of the SMBH is to use the empirical relations for estimating M[subscript(bh)] for larger samples of galaxies. The investigation of the SMBH population (or SMBH mass function) for large sample of galaxies in the nearby universe has helped to constrain the SMBH and the galaxy evolution. Previous estimates of the SMBH mass function at low redshift were produced mainly by combining the measurements of the galaxy luminosity or velocity function with one of the SMBH scaling relations. In the first part of the thesis I will present an independent construction of the nearby supermassive black hole mass function by applying the optical M[subscript(bh)]–L relation onto the Millennium Galaxy Catalogue (MGC). Additionally, in the second part I will provide photometric analysis of all UKIDSS galaxies for which SMBH masses have been measured. I will derive composite profiles of brightness, ellipticity and position angles of each galaxy. I will show that the Sérsic function fits the brightness profile of the majority of the elliptical galaxies and the bulge of disk galaxies and I will provide alternative multi-component fits when necessary. Then these photometric parameters will be used for constructing the M[subscript(bh)]–L relation in the near-IR and to investigate the M[subscript(bh)]–n relation. In the third part I will construct the near-IR SMBH mass function for the Galaxy and Mass Assembly (GAMA) survey. For this purpose I will apply the newly derived M[subscript(bh)]–L relation onto an elliptical subsample of K-band images. The advantage of this SMBH mass function is that during the M[subscript(bh)]–L construction I used the same quality images and techniques used on the GAMA survey. Apart from the M[subscript(bh)]–L relation, the M[subscript(bh)]–sigma relation was used as an alternative approach for a subsample of galaxies for which the velocity dispersions were available. Furthermore, I employed both local SMBH mass functions (MGC & GAMA) for estimating the SMBH mass density at redshift zero and accounted for the dependence of the total SMBH density on the look-back time by comparing with semi-analytic SMBH mass functions. Finally, from the SMBH mass density I estimated the baryon fraction that is locked into SMBHs.
50

Fotometría óptica desde el espacio: la cámara OMC a bordo de INTEGRAL

Domingo Garau, Albert 24 November 2011 (has links)
El trabajo que presentamos en esta tesis tiene como finalidad la operación, calibración y análisis de datos ópticos del instrumento OMC (Optical Monitoring Camera) a bordo del satélite INTEGRAL (INTErnational Gamma-Ray Astrophysics Laboratory). La cámara OMC ofrece, por primera vez, la oportunidad de realizar observaciones fotométricas de larga duración en el rango óptico, simultáneamente con las de rayos X y rayos gamma. En la primera parte de la tesis describimos el proyecto INTEGRAL/OMC y sus operaciones científicas, detallando el proceso que hemos seguido para la construcción del catálogo de entrada de la OMC. Definimos la estrategia y requisitos que debe satisfacer el software de apuntado encargado de generar los telecomandos que controlan el funcionamiento de la cámara. La combinación del catálogo y el software de apuntado, junto con el buen funcionamiento del algoritmo de centrado de a bordo, han permitido la determinación del apuntado de la OMC, a bordo y en tiempo real, con una precisión mejor que 1 píxel desde el inicio mismo de las operaciones. La segunda parte se centra en el procedimiento que hemos elaborado para el análisis de los datos. Describimos el flujo de datos desde que llegan a tierra, pasando por los distintos sistemas de procesamiento, hasta que, finalmente, se convierten en datos científicos listos para ser utilizados por la comunidad astrofísica. Detallamos todos los aspectos relacionados con la calibración del instrumento. Explicamos los distintos algoritmos desarrollados para el análisis científico de los datos OMC, haciendo especial énfasis en las soluciones adoptadas para mejorar los resultados fotométricos y astrométricos del instrumento. En la última parte presentamos los archivos y catálogos resultantes de las observaciones realizadas con la cámara OMC. Describimos los archivos de datos procesados en tiempo real y de datos consolidados, así como el portal Web de acceso a los datos OMC. Avanzamos lo que será el catálogo final de la OMC, que contendrá todas las fuentes observadas y detectadas por este instrumento, una vez finalizada la misión INTEGRAL. Presentamos también dos de los subcatálogos preliminares obtenidos tras analizar determinados grupos de fuentes: "Contrapartidas ópticas de fuentes de altas energías del 4º Catálogo IBIS/ISGRI" y "Primer catálogo de fuentes variables observadas con la OMC". / The work presented in this thesis describes the system that allows the operation, calibration and data analysis of the OMC instrument (Optical Monitoring Camera) on board the ESA's INTEGRAL spacecraft (INTErnational Gamma-Ray Astrophysics Laboratory). The OMC camera offers, for the first time, the opportunity to perform long photometric observations in the optical range simultaneously to those in the X-ray and gamma-ray bands. In the first part of the thesis we describe the INTEGRAL/OMC project and its scientific operations, giving some details about the building process of the OMC Input Catalogue. We define the strategy and requirements of the OMC Pointing Software which generates the telecommands to control the camera operations. The combination of both the Input Catalogue and the Pointing Software, as well as the excellent behaviour of the on-board centring algorithm, allow us the on-board determination in real time of the OMC pointing direction with an accuracy better than 1 pixel from the beginning of the mission operations. The second part is focused on the development involved in the data analysis procedures. We describe the data flow starting when the telemetry data are received at Earth, followed by the different data processing stages present in the systems, until they are finally converted into scientific data which can be used by the astrophysics community. We explain all aspects related to the instrument calibration and the algorithms developed for the OMC scientific analysis, making special emphasis in the adopted solutions that allowed us to improve the photometric and astrometric results. In the last part we present the archives and catalogues compiled with the OMC data obtained during INTEGRAL observations. We describe the consolidated and near real time data archives as well as the OMC Archive Web Portal. We summarize the contents of the final OMC Catalogue which will be published at the end of the INTEGRAL mission including all sources observed and detected by OMC. In addition we present two preliminary sub-catalogues obtained by analysing some specific objects groups: "OMC optical monitoring of sources in the 4th IBIS/ISGRI catalogue" and "The first INTEGRAL/OMC Catalogue of optically variable sources".

Page generated in 0.3403 seconds