Browsing by Author "Woudt, Patrick Alan"
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- ItemOpen AccessAccretion and outflow in black-hole x-ray binaries(2015) Dusoye, Avishek; Coriat, M; Woudt, Patrick AlanBlack hole X-ray binaries (BHXBs) are stellar binary systems consisting of a black hole (BH) and a companion star. They are known to produce X-ray emission through the accretion of mass from the companion star onto the black hole via an accretion disc, as well as radio emission originating from their jets. My thesis splits into two projects. On one hand, I focus on the connection between the X-ray emitting accretion disc and the radio jets of BHXBs in general, by studying the quasi-simultaneous evolution of the radio fluxes and the X-ray fluxes from 17 BHXBs. This connection, also known as the radio/X-ray correlation has been studied and updated over the past years. New observations of new and known sources have shown that another population of X-ray binaries exists (referred to as outliers), lying below the standard radio/X-ray correlation. I investigate whether the mass of the black hole component of BHXBs can explain the existence of these outliers. In my second project, I focus on an exotic source, known as SS433. It has a supercritical accretion disc and displays precessing relativistic jets. I investigate whether these jets are made up of proton-electron plasma or electron-positron plasma. Circular polarization (CP) is a good diagnostics for understanding the particle composition of radio jets. Therefore we have observed the circular polarized flux densities of SS433 using the Australia Telescope Compact Array (ATCA) for a broad range of frequencies between 1:4 - 10 GHz. From those observations, a CP spectrum can be constructed and the spectral index can be estimated. There are 4 ways of producing CP emission and the spectral index helps us to constrain the CP production mechanism. In addition, the kinematics of propelling a proton-electron plasma in a jet is different from that of electronpositron plasma. I simulate various plausible models for the energy content of the jets and thereby aim to constrain the particle composition of the jets. Black hole X-ray binaries (BHXBs) are stellar binary systems consisting of a black hole (BH) and a companion star. They are known to produce X-ray emission through the accretion of mass from the companion star onto the black hole via an accretion disc, as well as radio emission originating from their jets. My thesis splits into two projects. On one hand, I focus on the connection between the X-ray emitting accretion disc and the radio jets of BHXBs in general, by studying the quasi-simultaneous evolution of the radio fluxes and the X-ray fluxes from 17 BHXBs. This connection, also known as the radio/X-ray correlation has been studied and updated over the past years. New observations of new and known sources have shown that another population of X-ray binaries exists (referred to as outliers), lying below the standard radio/X-ray correlation. I investigate whether the mass of the black hole component of BHXBs can explain the existence of these outliers. In my second project, I focus on an exotic source, known as SS433. It has a supercritical accretion disc and displays precessing relativistic jets. I investigate whether these jets are made up of proton-electron plasma or electron-positron plasma. Circular polarization (CP) is a good diagnostics for understanding the particle composition of radio jets. Therefore we have observed the circular polarized flux densities of SS433 using the Australia Telescope Compact Array (ATCA) for a broad range of frequencies between 1:4 - 10 GHz. From those observations, a CP spectrum can be constructed and the spectral index can be estimated. There are 4 ways of producing CP emission and the spectral index helps us to constrain the CP production mechanism. In addition, the kinematics of propelling a proton-electron plasma in a jet is different from that of electron-positron plasma. I simulate various plausible models for the energy content of the jets and thereby aim to constrain the particle composition of the jets.
- ItemOpen AccessAccretion processes in magnetic cataclysmic variables - a detailed study of UZ Fornacis(2022) Khangale, Zwidofhelangani Ndamulelo; Woudt, Patrick Alan; Potter, Stephen BrianThis thesis presents a multi-wavelength exploration of the emissions from magnetic cataclysmic variable (mCV) stars with specific focus on the eclipsing AM Her system, UZ Fornacis (hereafter UZ For). The main objective of this thesis is to investigate the underlying emission mechanisms as well as the accretion dynamics in this system with the intention of increasing our understanding of this class of objects as a whole. The presence of a strong magnetic field in UZ For makes it an interesting object in terms of how the magnetic field dominates the accretion dynamics and its influence on the emission processes. The eclipsing characteristics of this system, with a clearly defined ingress and egress of the main accretion spot, can be exploited to gain further insights through precise eclipse timings. The first part of this thesis presents 33 new mid-eclipse times spanning eight years of observations on UZ For. The new observations are used to test the two-planet model previously proposed to explain the periodic variations in the eclipse times of UZ For measured over the past ∼35 years. The results show that the proposed model does indeed follow the general trend of the new eclipse times. However, there are significant departures. In order to accommodate the new eclipse times, the two-planet model requires that one or both of the planets have highly eccentric orbits, i.e. e ≥ 0.4. Such multiple planet orbits are considered to be unstable. Whilst our new observations are consistent with two cyclic variations as previously predicted, significant residuals remain. This study explores the possibility that either additional cyclic terms, possibly associated with more planets, or other mechanisms, such as the Applegate mechanism are contributing to the eclipse time variations. The second part of this thesis presents phase-resolved spectroscopy of UZ For which allowed us to do a detailed Doppler tomography study of this target. The averaged blue spectrum is dominated by single- and/or double-peaked emission from HeII 4686 Å and the Balmer lines, as well as weak emission from HeI lines and the CIII/NIII blend at 4650Å. The averaged red spectrum shows strong emission from CaII lines at 8498 Å and 8542 Å and possibly weak emission from the NaI doublet at 8183 Å and 8194 Å. The strength of HeII 4686 Å line is comparable to that of Hβ line and this is typical for AM Her systems in a high state of accretion. The ratio of Hγ/Hβ ' 1 implying that these emission lines were formed in an optically thick region, that is, a region of high optical depth in the lines. Doppler tomography of the strongest features in the blue, HeII 4686Å and the Balmer lines (e.g. Hβ line), using both the standard and inside-out maps, revealed the presence of three emission regions: 1) the irradiated face of the secondary star, 2) the ballistic stream and the threading region, and 3) the magnetically confined accretion stream. The Doppler maps of emission lines in the red spectrum show the presence of emission from the irradiated face of the secondary star as well as emission from various parts of the ballistic and magnetically confined accretion stream. Also presented are the respective modulation Doppler maps of each line. These show that both the ballistic and magnetically confined accretion stream are modulated as well as the irradiated face of the secondary star. In addition to the above, the first simultaneous optical and MeerKAT radio observations of the eclipsing AM Her system UZ For are also presented. The optical data include SALT circular spectropolarimetry taken around the eclipse and SHOC and MeerLICHT photometry. The total intensity spectrum shows broad emission features with the continuum that rises in the blue. The percentage circularly polarized spectra show that UZ For is negatively polarized (up to ∼ −8%) in the blue and decreasing gradually towards the red. The circularly polarized spectrum shows the presence of three cyclotron emission features at ∼4500 Å, 6000 Å and 7700 Å, corresponding to harmonic numbers 4, 3 and 2, respectively. These features are dominant before the eclipse and disappears after the eclipse. The harmonics are consistent with the magnetic field strength of ∼57 MG seen at a viewing angle of 70◦ . To aid with the interpretation of the circular spectropolarimetry, simultaneous circular and linear photopolarimetric observations of UZ For obtained with the HIPPO instrument several weeks leading to the SALT observations were also analysed. The results show that UZ For is ∼ −5% circularly and 5% linearly polarized before the eclipse. A burst of linear polarization is seen just after the eclipse reaching ∼10%. After the eclipse, negative circular polarization reaching ∼ −5% is observed. Both linear and circular polarization are consistent with zero after phase 1.1. The MeerKAT radio observations show a faint source which has a peak flux density of 30.7 ± 5.4 µJy/beam at 1.28 GHz (L-band) at the position of UZ For. This marks the first detection of UZ For at L-band. This study demonstrates that multi-wavelength observations are essential to understanding the various emission processes that are at work in mCVs. The results presented in this thesis shows that UZ For is one of the most interesting AM Her systems known to date. The circular spectropolarimetry results are consistent with those from literature and shows that the SALT telescope will be able to observe other systems like this for detailed analysis. Furthermore, the eclipse times of this system is consistent with the presence of two planets and makes UZ For the second AM Her system after HU Aqr shown to harbour planets and in which additional observations still support earlier conclusions. The radio detection of this system with MeerKAT opens a window to studying other low flux density AM Her systems at L-band radio frequencies in the southern sky.
- ItemOpen AccessThe deep optical ZoA galaxy catalogue in Vela first indications of previously hidden large-scale structures(2012) Von Maltitz, Kosma; Kraan-Korteweg, Renée C; Woudt, Patrick AlanThis thesis presents a deep optical galaxy catalogue of the Vela region in the Zone of Avoidance (I b < 10°.245 < I < 280. This region was searched for galaxy candidates by optical inspection of IIIaJ (3950 A to 5400 A) film copies of the ESO/SRC sky survey as part of an effort to reduce the ZoA.
- ItemOpen AccessA deep photometric survey of the Abell cluster SO423 : a pilot study for the UCT SALT supercluster survey(2007) Kotze, J P; Kraan-Korteweg, Renée C; Woudt, Patrick AlanIncludes bibliographical references (leaves 99-101).
- ItemOpen AccessThe nature and nature of a starburst supermassive H1 galaxy : HIZOA J0836-43(2008) Cluver, Michelle E; Kraan-Korteweg, Renée; Woudt, Patrick Alan; Jarrett, TomIncludes abstract.
- ItemOpen AccessA novel algorithm for analysing gravitational microlensing events(2012) Rajpaul, Vinesh; Menzies, John W; Stewart, I M; Woudt, Patrick AlanThis dissertation presents a new algorithm that was developed to perform autonomous fitting of gravitational microlensing lightcurves. The algorithm combines features of extant evolutionary algorithms with some novel ones, and fares well on the problem of fitting binary lens microlensing lightcurves, as well as on a number of other difficult optimisation problems. Furthermore, the new algorithm is conceptually simple, versatile and robust, and parallelises trivially.
- ItemOpen AccessPhotometry of elliptical galaxies in crowded starfields(2006) Markus, Karsten; Fairall, Anthony Patrick; Woudt, Patrick AlanIncludes bibliographical references.
- ItemOpen AccessProbing distant clusters : a pre-SALT photometric study of intermediate redshift galaxy cluster(2005) Cluver, Michelle E; Fairall, Anthony Patrick; Woudt, Patrick AlanIncludes bibliographical references (p. 273-279).
- ItemOpen AccessQuality control of astronomical CCD observations(2007) Tshenye, Thapelo Obed; Balona, Luis; Woudt, Patrick AlanIncludes bibliographical references (p. 111-113)
- ItemOpen AccessRapid oscillations in cataclysmic variable stars(2004) Pretorius, Magaretha L; Warner, Brian; Woudt, Patrick AlanRapid quasi-coherent oscillations were detected in the optical light curves of 24 cataclysmic variable stars (CVS). In 12 of these systems (TU Men, WW Cet, HX Peg, BP CrA, BR Lup, HP Nor, AG Hya, TW Vir, PU CMa, V426 Ooph, V1193 Ori, and CR Boo) for the first time. The results contribute to the observational record of the phenomenology of dwarf nova oscillations (DNOs), quasi-periodic oscillations (QPOs), and longer period dwarf nova oscillations (lpDNOs), strengthen the correlation, valid over nearly six orders of magnitude in frequency, between the ratio of time scales of different classes of oscillations in white dwarf, neutron star, and black hole binaries, and show that the recently recognized lpDNOs occur fairly commonly in high mass transfer rate CVs.
- ItemOpen AccessSALT spectropolarimetry commissioning(2010) Brink, Janus Daniel; Woudt, Patrick Alan; Buckley, David; Potter, Stephen;The large (10m) aperture of the Southern African Large Telescope (SALT) coupled with the unique capabilities of the Robert Stobie Spectrograph (RSS), promises unparalleled prospects for polarimetric observations on an 8 - 10 m class telescope. RSS is a complex and highly versatile first-generation instrument of the SALT. RSS-VIS, the visible arm spanning 320-900 nm, employs a high UV-transmitting optical design to support UV spectroscopy down to the atmospheric cutoff at 320nm (rare on large telescopes).
- ItemOpen AccessSpectral analysis of the helium nova V445 Puppis(2012) Macfarlane, Sally; Woudt, Patrick AlanMultifibre spectrographic observations of the bipolar helium nova V445 Puppis were made over fivenights (two nights in January 2006 and three nights in January 2007) using the IMACS Integral Field Lnit spectrograph on the Magellan I Telescope. Of these. spectra from the two best nights. 4 January 2006 and 8 January 2007, were reduced. extracted. calibrated and analysed in this thesis. The spectra extracted from sewn target frames in 2006 and six target frames in 2007 were combined for -100 individual fibres. The two-dimensional spectra were then recombined into a data cube to create a three-dimensional picture of the emission from the nova.
- ItemOpen AccessA spectroscopic analysis of the eclipsing Nova-like EC21178-54(2013) Khangale, Zwidofhelangani Ndamulelo; Woudt, Patrick AlanEC21178-54 is a 13.7 magnitude eclipsing nova-like (NL) cataclysmic variable (CV) discovered in the Edinburgh-Cape survey of blue objects. It has an orbital period of 3.708 hours. High-speed photometric analysis of its light curve reveal that this system is a rich source of quasi-periodic oscillations (QPOs), dwarf nova oscillations (DNOs) and the other type of periodic oscillations called longer period dwarf nova oscillations (lpDNOs). Its light curve shows a deep symmetrical V-shaped primary eclipse, and its spectra show strong broad double-peaked emission. In this project we present phase-resolved spectroscopy of the eclipsing nova-like CV EC21178-54. The average spectrum of EC21178-54 shows broad double-peaked emission lines from HeII 4686Ã…, and the Balmer series. HeII 4686Ã… dominates the Balmer lines; and in the Balmer lines the blueshifted component is the stronger of the two. The high-excitation feature, CIII/NIII at 4640-4650 Ã…, is also present and appear broad in emission. A number of other lines, mostly HeI, are clearly present in absorption and/or emission.
- ItemOpen AccessStudying the environmental dependence of star formation properties of galaxies in the Abell 1437 galaxy cluster and its surrounding large scale structure(2014) Kotze, J P; Kraan-Korteweg, Renée C; Woudt, Patrick Alan; Väisänen, Petri; Gilbank, DavidIt has become clear that the local galaxy environment plays a crucial role in the evolution of galaxies. Recent studies show a strong bimodal distribution of galaxy properties, with red, passive galaxies dominating the bimodal distribution in dense environments, compared to blue, actively star forming galaxies dominating the bimodal distribution in low density environments. Blue, star-forming galaxies are continuously transformed into red, passive galaxies through one or more processes while being accreted into higher density environments. The processes responsible for the observed transformation remain uncertain. We address these issues by performing an in-depth study of large-scale structure surrounding the galaxy cluster Abell 1437 at z = 0.135. We consider the colour and specific star formation rate distributions of galaxies as a function of environment. In this thesis we develop techniques to derive environmental samples which consist of a cluster, groups, filament and field. The large-scale structure surrounding the cluster is characterised through the use of a Friends-of-Friends algorithm based on spectroscopic data. This provides a reference from which we construct a photometric environmental catalogue using methods developed to find groups and define filamentary structure. To accomplish this, we construct a ugrizJHK multi-band dataset using a custom pipeline to derive a seeing matched photometric catalogue from Sloan Digital Sky Survey (SDSS) and UKIRT Deep Sky Survey (UKIDSS) imaging data. The photometric dataset is complemented by a near uniformly sampled spectroscopic dataset from the SDSS and Two Degree Field (2dF) survey. Stellar masses and star formation rates for the environmental samples are derived using the state-of-the-art magphys SED fitting code. The environmental samples we derive yield, within the uncertainties, similar galaxy populations than typically found in clusters, groups and the field. Red fractions were computed for the cluster, groups, filament and field sample for which we found 0.90 ± 0.13, 0.79 ± 0.01, 0.69 ± 0.02 and 0.58 ± 0.01 respectively. This is the first filament red fraction measurement made in this way. We studied the passive fraction of galaxies as a function of environment using specific star formation rates. Passive fractions were computed using two different definitions of passiveness, 1/tH (log(sSFR) = −10.07) and the minimum in the bimodal sSFR distribution (log(sSFR) = −11.0) as the division between active and passive galaxies. We found that the log(sSFR) = −11.0 bimodal divider is a natural division between active and passive galaxies and does not suffer from density-dependent selection effects. Quiescent fractions derived from the environmental samples reproduce previously known trends of star formation rates with environment. The filament environment is one of the least well studied environments since their low galaxy density makes them difficult to detect. We studied the fractional excess of star forming galaxies along the filament between Abell 1437 and the neighbouring region of overdensities, and find a significant increase in star formation activity. Although there have been hints of excess star formation in filaments previously, we claim our results to be of highest significance thus far.
- ItemOpen AccessTime-series photometry and spectroscopy of the cataclysmic variable EC21178-5417 : exploring new avenues with the Southern African Large Telescope.(2008) Zietsman, E; Woudt, Patrick AlanIncludes abstract. Includes bibliographical references.