Browsing by Author "Menzies, John"

Now showing 1 - 4 of 4
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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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    The detection of gravitational microlensing anomalies
    (1999) Vermaak, Pierre le Roux; Menzies, John; Warner, Brian
    The detection and measurability of microlensing anomalies including planet detection, resolved source, blending and parallax effects are investigated by way of an extensive computer simulation as a function of the observation strategy. The most efficient strategy has a planet detection probability exceeding 753 for the most favourable binary geometry, while results for typical event follow up and survey observations agree well with previous work. A complex dependence of planet detection on the resolved source radius is discovered leading to a possible increase in the probability of detecting planets with mass ratios smaller than q = 10⁻³
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    Gravitational microlensing and the search for extrasolar planets
    (2013) Mengistie, Getachew Mekonnen; Feast, Michael; Menzies, John
    This project is aimed at tackling binary gravitational microlensing events. Since the early conception of gravitational lensing before Einstein’s General Theory of Relativity, physicists and astronomers of the early 18th century speculated that light, if treated as particle, can be affected by gravitational field. Gravitational Microlensing is defined as a phenomenon occurring when light coming from a distant (source) star is bent by the gravitational field of an intervening mass (lens) creating multiple image of the source which cannot be resolved. In this project, We applied a model for binary lens microlensing events. We analysed data obtained from different observatories: PLAXET, which includes SAAO, Sutherland, Canopus and Perth observatories, OGLE, Danish Telescope, LaSilla. For the observed microlensing target OGLE-2011-BLG-265, analysis of the data using the program supplied by Keith Horne, using different minimization schemes and algorithms, I found best fit model to be a binary lens with mass ratio q = 0.0042 and separation of components is found to be u = 1.034 where in this case the separation falls under an intermediate binary lens topology. Finally, the deviation from the point-source point-lens microlensing events on the light curve and small mass ratio suggested a planetary system. I also calculated the time, tp, that the source needs to cross the diameter of the planet Einstein Ring radius, which is related to the mass ratio, and is found to be 3.30 days.
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    The red clump stars as a distance indicator : review and application
    (2002) Peter, Camaren; Menzies, John
    The intention of this project was primarily to determine the distance to the Galactic Centre using a new technique pioneered by Paczynski and Stanek (1998) that uses the red clump stars as a standard candle. This was made possible by the large number of stars simultaneously observed by the OGLE microlensing project which yields well-defined red clump structures in their colour magnitude diagrams. We have used data obtained at Sutherland in July 1997, in collaboration with the PLANET microlensing project. It was hoped that the observation of a number of lensing events occurring in fields in the Galactic Bulge region would reveal information about the Galactic structure in that region and perhaps yield information about the lens masses. The red clump technique is reviewed and applied to several 3x 3 arcminfields observed at low galactic latitude and longitude in the Galactic Bulge. The derived distances to the fields show consistency with the E2 bar model proposed by Stanek, and indicate that the distance from our sun to the Galactic Centre is 7.97± 0.4 kpc. Furthermore, an attempt is made to apply the derived individual distance to each field to calculate the possible lens mass associated with each event.