Browsing by Author "Whitelock, Patricia A"

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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.
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    Characterization of the atmospheric turbulence at the Sutherland site and conceptual design study and optimization of an Adaptive Optics system for the Southern African Large Telescope
    (2017) Catala, Laure; Crawford, Steve M; Whitelock, Patricia A; Buckley, David A H
    To support the potential development of an AO system for SALT, a site monitoring campaign of the Sutherland site was initiated in 2010. This campaign also led to the participation in the development of a new instrument to characterize the atmospheric turbulence. The results from five years of site testing were used in AO simulations in order to demonstrate the potential capabilities of an AO system on SALT. The site testing study produced up-to-date seeing values and provided a measurement of the atmospheric turbulence profiles. I found a median seeing value of 1.51". The main contributor to the turbulence is clearly the ground layer, below 1 km, responsible for 83% of the turbulence. The next most significant contributor is the wind shear layer around 3 km. Seasonal trends show that slightly worse seeing conditions occur during the winter months due to predominant East, South-easterly winds that are associated with degraded seeing conditions. In addition to the main site testing campaign, I helped develop the "Profileur de Bord Lunaire" (PBL, Profiler of Moon limb in English), a new instrument that uses the Moon limb to measure the atmospheric turbulence profile. The work on the data processing and inversion method led to the extraction of high altitude-resolution profiles of the turbulence strength. I present here those results along with a comparison with profiles obtained with the Multi-Aperture Scintillation Sensor (MASS). Using the results from the site testing campaign along with the SALT optical design, I simulated the general dimensioning of a system for SALT that would use a single natural guide star (NGS). The trade-off between performances and sky coverage resulted in a 34x34 system using NGS in the range 10 to 14 magnitude in R-band. The 34x34 dimensions refer to the number of subapertures of the Shack-Hartmann wavefront sensor. I conclude with the significant improvement in spectroscopic performance for SALT that could be achieved by implementing an AO system. The gains in encircled/enslited energy are most significant in the near infrared where gains of 183% could be achieved at 1600 nm for the planned Near-infrared upgrade to the Robert Stobie Spectrograph (RSS). The gains in enslited and encircled energy at 700 nm for the visible arm of RSS and the High-Resolution Spectrograph (HRS) are limited to a maximum of 22% and 34%, respectively, due to the large apertures adapted to seeing-limited observations. Further gains could be achieved by designing the next generation of SALT instrumentation to take full advantage of an AO system.
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    Photometric techniques for exoplanet detection: the construction and deployment of the KELT-South telescope
    (2014) Kuhn, Rudolf Bruwer; Whitelock, Patricia A; Menzies, John W
    In this thesis I present the work I performed during the initial construction and deployment of the second telescope in the KELT project and I report the results of the search for transiting exoplanets and variable stars using one of the first commissioning datasets obtained with the telescope. The KELT-South telescope is located in Sutherland, South Africa and construction started in 2008. The telescope has been operating at full capacity since 2010, after two commissioning seasons from late 2008 to early 2010. I developed all the code that allows it to be fully automatic and robotic and over the last 5 years I have been responsible for the observing operations and general maintenance of the telescope. I also developed many other software tools that help with the identification of the exoplanet candidates. The Kilodegree Extremely Little Telescope (KELT) project at present consists of two robotic, wide field, small aperture telescopes that are designed primarily to find transiting exoplanets around bright stars in the magnitude range 8 < V < 11. Transiting planets orbiting bright stars can be studied with intense follow-up programs with relative ease on larger telescopes, making them favourable targets to determine the atmospheric composition of the planet as well as a host of other properties that cannot be obtained from planets orbiting fainter stars. Of the known 1811 (August 2014) exoplanets only 60 are transiting stars with V < 11 and only 16 of those have been found from the southern hemisphere. The discovery of more of these exoplanets will help constrain the theories of formation and evolution of short period, gas giant exoplanets. Data reduction on one of the commissioning datasets was completed in 2012. The dataset spans 46 days and lightcurves for 78297 objects were obtained. I performed a search for periodicities in the lightcurves and found that 1411 stars showed clear signs of variability and these objects were compiled into a catalogue of possible variable stars. 1018 of the catalogue members were not previously known to be variable. I searched for planetary transits and eight possible exoplanet candidates were identified. Photometric follow-up observations of two targets eliminated them as exoplanet candidates, each being a blended eclipsing binary system. The remaining six candidates are awaiting follow-up observations at present. Although the commissioning dataset served primarily to refine the data reduction pipeline and the procedures I used to find variable stars, I have demonstrated that the KELT-South telescope is capable of detecting the kinds of signals required for exoplanet discovery.
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    Robotic control of a photometric telescope
    (2011) Van Heerden, Hendrik Petrus; Whitelock, Patricia A; Martinez, Peter
    The objective of this project was to design and implement the telescope control software for the Alan Cousins Telescope (ACT), a robotic telescope at the Sutherland, South Africa, site of the South African Astronomical Observatory (SAAO). The approach adopted involved a high level of modularisation of the software and the use of software simulators in an effort to foster rapid software development and enable more rigorous software testing. Significant attention was also paid to new and emerging technologies and how these may be used within the specific context of robotic telescope control software. The software now acts as a demonstration platform for those technologies that were implemented.
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    SPIRITS: Uncovering Unusual Infrared Transients with Spitzer
    (2017) Kasliwal, Mansi M; Bally, John; Masci, Frank; Cody, Ann Marie; Bond, Howard E; Jencson, Jacob E; Cao, Yi; Boyer, Martha; Cantiello, Matteo; Cook, David; Hsiao, Eric; Khan, Rubab M; Milne, Peter; Morrell, Nidia; Ofek, Eran O; Perley, Daniel A; Phillips, Mark; Prince, Thomas A; Shenoy, Dinesh; Surace, Jason; Dyk, Schuyler D Van; Whitelock, Patricia A; Williams, Robert
    We present an ongoing, five-year systematic search for extragalactic infrared transients, dubbed SPIRITS—SPitzer InfraRed Intensive Transients Survey. In the first year, using Spitzer /IRAC, we searched 190 nearby galaxies with cadence baselines of one month and six months. We discovered over 1958 variables and 43 transients. Here, we describe the survey design and highlight 14 unusual infrared transients with no optical counterparts to deep limits, which we refer to as SPRITEs (eSPecially Red Intermediate-luminosity Transient Events). SPRITEs are in the infrared luminosity gap between novae and supernovae, with [4.5] absolute magnitudes between −11 and −14 (Vega-mag) and [3.6]–[4.5] colors between 0.3 mag and 1.6 mag. The photometric evolution of SPRITEs is diverse, ranging from <0.1 mag yr{sup −1} to >7 mag yr{sup −1}. SPRITEs occur in star-forming galaxies. We present an in-depth study of one of them, SPIRITS 14ajc in Messier 83, which shows shock-excited molecular hydrogen emission. This shock may have been triggered by the dynamic decay of a non-hierarchical system of massive stars that led to either the formation of a binary or a protostellar merger.