Browsing by Department "Department of Astronomy"

Now showing 1 - 20 of 285
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    2MASS J0516288+260738: Discovery of the first eclipsing late K + Brown dwarf binary system?
    (2003) Schuh, S L; Handler, G; Drechsel, H; Hauschildt, P; Dreizler, S; Medupe, R; Karl, C; Napiwotzki, R; Kim, S-L; Park, B-G; Wood, M A; Paparó, M; Szeidl, B; Virághalmy, G; Zsuffa, D; Hashimoto, O; Kinugasa, K; Taguchi, H; Kambe, E; Leibowitz, E; Ibbetson, P; Lipkin, Y; Nagel, T; Göhler, E; Pretorius, M L
    We report the discovery of a new eclipsing system less than one arcminute south of the pulsating DB white dwarf
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    A cataclysmic key program for SALT
    (2006) Warner, Brian
    The study of cataclysmic variable stars has a long history in South Africa. A brief overview of this history is followed by indications of where the new Southern African Large Telescope (SALT) is likely to make major contributions to this research field. There are about 60 staff and students in the SALT Consortium, who work on interacting binaries containing compact components. Most of these people work on cataclysmic variable stars, with the remainder researching neutron star and black hole binary pairs. This group will use a significant amount of SALT observing time. I look at some of the collective and individual topics that SALT will be able to address.
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    A catalogue of galaxies behind the southern Milky Way: II. The Crux and Great Attractor regions ($lapprox$ 289° to 338°)
    (2001) Woudt, P A; Kraan-Korteweg, R C
    In this second paper of the catalogue series of galaxies behind the southern Milky Way, we report on the deep optical galaxy search in the Crux region (
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    A high-dispersion molecular gas component in nearby galaxies
    (2013) Caldú-Primo, Anahi; Schruba, Andreas; Walter, Fabian; Leroy, Adam; Sandstrom, Karin; de Blok, W J G; Ianjamasimanana, R; Mogotsi, K M
    We present a comprehensive study of the velocity dispersion of the atomic (H I) and molecular (H2) gas components in the disks (R R 25) of a sample of 12 nearby spiral galaxies with moderate inclinations. Our analysis is based on sensitive high-resolution data from the THINGS (atomic gas) and HERACLES (molecular gas) surveys. To obtain reliable measurements of the velocity dispersion, we stack regions several kiloparsecs in size, after accounting for intrinsic velocity shifts due to galactic rotation and large-scale motions. We stack using various parameters: the galactocentric distance, star formation rate surface density, H I surface density, H2 surface density, and total gas surface density. We fit single Gaussian components to the stacked spectra and measure median velocity dispersions for H I of 11.9 ± 3.1 km s–1 and for CO of 12.0 ± 3.9 km s–1. The CO velocity dispersions are thus, surprisingly, very similar to the corresponding ones of H I, with an average ratio of σH I /σCO= 1.0 ± 0.2 irrespective of the stacking parameter. The measured CO velocity dispersions are significantly higher (factor of ~2) than the traditional picture of a cold molecular gas disk associated with star formation. The high dispersion implies an additional thick molecular gas disk (possibly as thick as the H I disk). Our finding is in agreement with recent sensitive measurements in individual edge-on and face-on galaxies and points toward the general existence of a thick disk of molecular gas, in addition to the well-known thin disk in nearby spiral galaxies.
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    A low H I column density filament in NGC 2403: signature of interaction or accretion
    (2014) de Blok, W J G; Keating, K M; Pisano, D J; Fraternali, F; Walter, F; Oosterloo, T; Brinks, E; Bigiel, F; Leroy, A
    Observed H i accretion around nearby galaxies can only account for a fraction of the gas supply needed to sustain the currently observed star formation rates. It is possible that additional accretion occurs in the form of low column density cold flows, as predicted by numerical simulations of galaxy formation. To constrain the presence and properties of such flows, we present deep H i observations obtained with the NRAO Green Bank Telescope of an area measuring 4° × 4° around NGC 2403. These observations, with a 5σ detection limit of 2.4 × 1018 cm-2 over a 20 km s-1 linewidth, reveal a low column density, extended cloud outside the main H i disk, about 17′ (~ 16 kpc or ~ 2 R25) to the NW of the center of the galaxy. The total H i mass of the cloud is 6.3 × 106 M⊙, or 0.15 percent of the total H i mass of NGC 2403. The cloud is associated with an 8 kpc anomalous-velocity H i filament in the inner disk, that was previously observed in deep VLA observations. We discuss several scenarios for the origin of the cloud, and conclude that it is either accreting from the intergalactic medium, or is the result of a minor interaction with a neigboring dwarf galaxy
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    A rare example of low surface-brightness radio lobes in a gas-rich early-type galaxy: the story of NGC 3998
    (2016) Frank, Bradley S; Morganti, Raffaella; Oosterloo, Tom; Nyland, Kristina; Serra, Paolo
    We study the nearby lenticular galaxy NGC 3998. This galaxy is known to host a low-power radio AGN with a kpc-size one-sided jet and a large, nearly polar H i disc. It is therefore a good system to study to understand the relation between the availability of cold-gas and the triggering of AGNs in galaxies. Our new WSRT data reveal two faint, S-shaped radio lobes extending out to ~10 kpc from the galaxy centre. Remarkably, we find that the inner H i disc warps back towards the stellar mid-plane in a way that mirrors the warping of the radio lobes. We suggest that the polar H i disc was accreted through a minor merger, and that the torques causing it to warp in the inner regions are also responsible for feeding the AGN. The “S” shape of the radio lobes would then be due to the radio jets adapting to the changing angular momentum of the accreted gas. The extended radio jets are likely poorly collimated, which would explain their quick fading and, therefore, their rarity in galaxies similar to NGC 3998. The fuelling of the central super-massive black hole is likely occurring via “discrete events”, suggested by the observed variability of the radio core and the extremely high core dominance, which we attribute to the formation and ejection of a new jet resulting from a recent fuelling event.
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    A simple model for global H i profiles of galaxies
    (2014) Stewart, I M; Blyth, S- L; de Blok, W J G
    Context. Current and future blind surveys for H i generate large catalogs of spectral lines for which automated characterisation would be convenient.
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    A spectral and timing study of MAXI J1820+070 during outburst
    (2024) Solomons, Kyle; Monageng, Itumeleng
    Black Hole X-ray binaries (BHXRBs) represent a unique class of astrophysical systems where a stellar-mass black hole accretes matter from a companion star via accretion disks. The accretion disk emits in X-ray and UV because of the radiative losses. The transfer of matter can occur through continuous donor supply or episodic capturing of material from stellar winds, leading to sudden enhancements in X-ray flux known as outbursts. The instabilities in the disk, the geometry of the inner disk, the coupling between the disk and corona, etc, also contribute to the observed variability. The exploration of BHXBs contributes significantly to our understanding of the broader astrophysical landscape. These offer a unique testing ground for theories related to accretion physics, extreme gravity, jet formation, and the evolution of binary systems. Moreover, the BHXBs play a pivotal role in shaping galactic dynamics and evolution in their neighbourhood. Among the myriad BHXBs, MAXI J1820+070 stands out as a particularly intriguing target. This low-mass X-ray binary, located in the constellation Ophiuchus, garnered attention due to its exceptional outburst in March of 2018. The intense luminosity of MAXI J1820+070, which reached a peak X-ray flux of ∼ 4 Crab, allowed for detailed multi-wavelength campaigns, facilitating comprehensive investigations into its properties and behaviour. MAXI J1820+070 provides a unique opportunity to deepen our understanding of accretion processes near black holes, enabling the refinement of theoretical models and enhancing our ability to interpret observations across the electromagnetic spectrum. This study presents a comprehensive analysis of the archival X-ray data of MAXI J1820+070 from NuSTAR, NICER, and Swift-XRT. The investigation focusses primarily on the system's spectral properties and timing characteristics. Spectral evolution and transitions between the hard and soft states are examined, with key parameters defining these states extracted. The inner disk radius was constrained to ≲ 2.6 ISCO, extending down to 1.5 ISCO before the state transition. The disk temperature steadily increases from 0.71 keV, peaking at 0.8 keV. Our simplistic spectral model prefers different inclinations at various stages of the outburst, varying from ∼ 45 to 73 degrees, probably due to the model's limitations. Furthermore, the power-law index was restricted to ∼ 1.6 and the coronal electron temperature to ∼24-38 keV. We identify the presence and evolution of quasi-periodic oscillations and quantify them through Lorentzian curve fitting. Additionally, we identified hard and soft time lags, varying in amplitude and frequency during the outburst. Together, the spectral and timing results suggest a QPO originating from the corona, with the corona contracting during the hard state and expanding during the state transition. Possible signatures of outflows are detected through absorption features between 6.9-7.3 keV.
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    A study of the galactic star cluster NGC 2547
    (1955) Fernie, John Donald
    The following thesis has been undertaken primarily as an observational study. Accordingly, theoretical discussion and speculations have been kept to a minimum, formulas in most case being early quoted and references given for their derivations. Since the observational techniques used are nearly all in standard practice, they have not been fully described, while descriptions of their reductions have been relegated to appendices.
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    Accretion and outflow in black-hole x-ray binaries
    (2015) Dusoye, Avishek; Coriat, M; Woudt, Patrick Alan
    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 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.
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    Accretion disks in the cataclysmic variables
    (1976) Koen, Marthinus Christoffel
    The general equations describing the time-independent structure of gaseous circumstellar disks in vertical hydrostatic equilibrium are derived. The possibility of turbulent instablilty and the resulting viscosity laws are discussed.
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    Accretion processes in cataclysmic variable stars: insights from optical transient surveys
    (2024) Motsoaledi, Mokhine; Woudt, Patrick; Buckley, David; Warner, Brian
    Cataclysmic variable (CV) stars are binary stars mostly characterised by accretion from a main sequence donor star to a white dwarf star. Multiple CV subclasses exist with varia tions in the nature of the CV, many of which have accretion discs surrounding the accretor. This study focuses on two sub-classes of CVs, namely AM Canum Venaticorum (AM CVn) stars with helium accretion from a (semi-)degenerate helium star or white dwarf donor star, and magnetic CVs, specifically polars, which have the strongest magnetic fields of the accreting white dwarfs in CVs and lack accretion discs. I make use of optical transient surveys to explore individual objects, as well as the global population of polars, with a focus on the Catalina Real-time Transient Survey (CRTS). Follow-up observations were carried out with the 1-m and 1.9-m telescopes and the 10-m Southern African Large Telescope (SALT) at the South African Astronomical Observatory (SAAO). Observations of 7 outbursting AM CVn stars with orbital periods ranging from
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    Accretion processes in magnetic cataclysmic variables - a detailed study of UZ Fornacis
    (2022) Khangale, Zwidofhelangani Ndamulelo; Woudt, Patrick Alan; Potter, Stephen Brian
    This 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.
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    Accurate classification of 29 objects detected in the 39 month Palermo Swift /BAT hard X-ray catalogue
    (2012) Parisi, P; Masetti, N; Jiménez-Bailón, E; Chavushyan, V; Palazzi, E; Landi, R; Malizia, A; Bassani, L; Bazzano, A; Bird, A J; Charles, P A; Galaz, G; Mason, E; McBride, V A; Minniti, D; Morelli, L; Schiavone, F; Ubertini, P
    Through an optical campaign performed at 4 telescopes located in the northern and the southern hemispheres, plus archival data from two on-line sky surveys, we have obtained optical spectroscopy for 29 counterparts of unclassified or poorly studied hard X-ray emitting objects detected with Swift/BAT and listed in the 39 months Palermo catalogue. All these objects have also observations taken with Swift/XRT or XMM-EPIC which not only allow us to pinpoint their optical counterpart, but also to study their X-ray spectral properties (column density, power law photon index and F2-10 keV flux). We find that 28 sources in our sample are AGN; 7 are classified as type 1 while 21 are of type 2; the remaining object is a galactic cataclysmic variable. Among our type 1 AGN, we find 5 objects of intermediate Seyfert type (1.2-1.9) and one Narrow Line Seyfert 1 galaxy; for 4 out of 7 sources, we have been able to estimate the central black hole mass. Three of the type 2 AGN of our sample display optical features typical of the LINER class and one is a likely Compton thick AGN. All galaxies classified in this work are relatively nearby objects since their redshifts lie in the range 0.008-0.075; the only galactic object found lies at an estimated distance of 90 pc. We have also investigated the optical versus X-ray emission ratio of the galaxies of our sample to test the AGN unified model. For them, we have also compared the X-ray absorption (due to gas) with the optical reddening (due to dust): we find that for most of our sources, specifically those of type 1.9-2.0 the former is higher than the latter confirming early results by Maiolino et al. (2001); this is possibly due to the properties of dust in the circumnuclear obscuring torus of the AGN.
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    Accurate Recovery of H i Velocity Dispersion from Radio Interferometers
    (2017) Ianjamasimanana, R; Blok, W J G de; Heald, George H
    Gas velocity dispersion measures the amount of disordered motion of a rotating disk. Accurate estimates of this parameter are of the utmost importance because the parameter is directly linked to disk stability and star formation. A global measure of the gas velocity dispersion can be inferred from the width of the atomic hydrogen (H I) 21 cm line. We explore how several systematic effects involved in the production of H I cubes affect the estimate of H I velocity dispersion. We do so by comparing the H I velocity dispersion derived from different types of data cubes provided by The H I Nearby Galaxy Survey. We find that residual-scaled cubes best recover the H I velocity dispersion, independent of the weighting scheme used and for a large range of signal-to-noise ratio. For H I observations, where the dirty beam is substantially different from a Gaussian, the velocity dispersion values are overestimated unless the cubes are cleaned close to (e.g., ˜1.5 times) the noise level.
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    An analysis of beta cephei stars in NGC 3293 and the effects of stellar rotation
    (1994) Engelbrecht, Christian Albertus; Balona, Luis; Warner, Brian
    An intensive photometric study in the Johnson B band of ten β Cephei stars in the open cluster NGC 3293 is presented. High sampling rates of the stars' light curves allow the identification of many formerly unknown pulsation frequencies in these stars, by means of Fourier periodogram analysis. All of the stars are found to be multiperiodic, with up to five frequencies identified for individual stars. Physical parameters of the stars are determined from previous photometric results in the literature. These parameters are used to make a comparison of the observed frequencies with theoretical predictions, including the effects of rotation. The results imply a preference for first and second overtone quadrupole (l=2) pulsation in these stars, while a weak relationship between stellar mass and pulsation overtone is identified. One of the stars is identified as a member of an eclipsing binary system, only the second β Cephei star to be identified as such. Physical parameters of the system are determined. The effects of rapid rotation (specifically, the distortion of the stellar profile from a perfect sphere) on alternative methods of pulsation mode identification are investigated for a model β Cephei star. Ratios between light and velocity amplitudes show extreme differences between rotationally distorted and undistorted models, but these ratios show high sensitivity to other parameters as well. Thermally broadened spectral line profiles are calculated for the same model, for modes with l = 0 to 4 and equatorial rotation velocities up to 400 km/s. Neglect of rotational distortion is shown to lead to underestimation of true equatorial rotation velocities by as much as 253. This result confirms that observed B stars are probably rotating at break-up velocities. In summary, various aspects of the behaviour of the β Cephei stars in NGC 3293 in particular, and of β Cephei stars in general, including rapid rotators, are illuminated and augmented by this study.
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    Analysis of SALT Fabry-Pérot medium resolution data
    (2015) Tapsoba, Wendyam Blaise; Williams, Theodore; Carignan, Claude; Lucero, Danielle M
    The Southern African Large Telescope Fabry-Pérot interferometer has been used in its medium resolution mode to observe three of 30 galaxies of the MHONGOOSE galaxy sample for which very deep HI observation (typically 200 hours/galaxy) will be obtained with MeerKAT. So optical high spatial resolution of 2 arcsec data of NGC 7361, NGC 7424 and NGC 7793 have been obtained. The major object of this thesis was to test SALT Fabry-Pérot medium resolution data in order to pursue the survey of all the MHONGOOSE sample, and to be able to compare the accuracy of the kinematic results. Through this work, some FORTRAN based routines have been improved and they allow us to compute kinematic maps with good accuracy. Indeed, the velocities measured from the profiles of the Hα emission in the data cube are accurate with the range of 1 km s⁻¹ to 10 km s⁻¹. So, we computed the kinematic maps and the rotation curves of the three galaxies using DiskFit and ROTCUR. For NGC 7361 and NGC 7424 we compared the rotation curves derived by both methods. For NGC 7793 we were also able to compare our results with previous studies.
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    Aperture synthesis imaging of the carbon AGB star R Sculptoris: Detection of a complex structure and a dominating spot on the stellar disk
    (2017) Wittkowski, M; Hofmann, K-H; Höfner, S; Le Bouquin, J B; Nowotny, W; Paladini, C; Young, J; Berger, J-P; Brunner, M; de Gregorio-Monsalvo, I; Eriksson, K; Hron, J; Humphreys, E M L; Lindqvist, M; Maercker, M; Mohamed, S; Olofsson, H; Ramstedt, S; Weigelt, G
    Aims. We present near-infrared interferometry of the carbon-rich asymptotic giant branch (AGB) star R Sculptoris (R Scl).
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    AST3002F: Reduction Guide (2018)
    (2018) Titus, Naomi; Woudt, Patrick
    The AST3002F spectroscopy practical involves the reduction and analysis of SALT spectroscopy of candidate white dwarfs in the Kepler field. The data are associated with a SALT Science project (2016-1- SCI-038). The reduction guide describes, step-by-step, the reduction process for the spectroscopic practical which includes a number of steps, namely: - a visual inspection of the spectra - removal of cosmic rays - wavelength calibration - sky subtraction - extraction of the spectrum of the primary target - extraction of the spectrum of other stars near the target
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    Asymptotic giant branch variables in NGC 6822
    (2010) Nsengiyumva, Francois; Whitelock, Patricia A; Menzies, John; Feast, Michael
    NGC 6822, a Local Group dwarf irregular galaxy, was observed in the nearinfrared JHKS bands using the Japanese-SAAO Infrared Survey Facility (IRSF) telescope over a period of about four years. An extensive search for large amplitude asymptotic giant branch variables over the observed 7.5' x 21.1' area of NGC 6822 found 162 probable variables. In particular, 30 Miras and 9 semiregulars have been identified and characterised.