Thesis (Ph. D.)--University of Wisconsin--Madison, 1974. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

This thesis presents the initiation of a multi-site photometric programme to examine the extraordinary behaviour displayed by 18 R Coronae Borealis (RCB) stars in the Magellanic Clouds (MCs). RCB stars exhibit a unique variability whereby they undergo rapid declines of up to several magnitudes. The decline may take several weeks, whereas the recovery to maximum light may take months or even years. The accepted wisdom for the cause of these enigmatic declines is a phenomenon whereby dust formed in the stellar environment reduces the brightness by as much as eight magnitudes (Clayton 1996). This is followed by the recovery phase during which the dust becomes homogeneously distributed in the stellar environment. The monitoring programme comprised the collection of UBVRI photometric data using five telescopes located at three different southern hemisphere longitudes (Las Campanas Observatory in Chile, Mount John University Observatory (MJUO) in New Zealand and the Southern African Large Telescope (SALT) in South Africa). The Optical Gravitational Lensing Experiment (OGLE), that operates at Las Campanas Observatory, provided the longest extent of data (December 1994 to February 2008). This was supplemented by data collected with telescopes at MJUO (September 2007 to January 2008) and SALTICAM on SALT (October 2007 to February 2008). Data calibration across the five instruments was a key element of the analysis, and entailed the use of F116 (an F region standard star) and other tertiary standards. Two important RCB characteristics, the enigmatic declines and the pulsational variability, form the bulk of the analysis presented in this thesis. Examination of the data acquired in the V and I filters resulted in the identification of a total of 18 RCB declines occurring in four stars (three stars in the Large Magellanic Cloud (LMC) and one in the Small Magellanic Cloud (SMC)). Construction of colour-magnitude diagrams (V −I vs V ), during the recovery to maximum light were undertaken in order to study the unique colour behaviour associated with the RCB declines. The combined recovery slope for the four stars was determined to be [(delta V)/(delta(V −I))] = 3.37 ± 0.24, which is similar to the value of [(delta V)/(delta(V −I))] = 3.1 ± 0.1 calculated for galactic RCB stars (Skuljan et al. 2003). In addition, the slopes calculated for the stars in the LMC ([(delta V)/(delta(V −I))]LMC = 3.34 ± 0.21) and SMC ([(delta V)/(delta((V −I))]SMC = 3.21 ± 0.22) alone, also agree to within their uncertainty. These results may imply that the nature of the dust (i.e. the particle size) is similar in both our Galaxy and the MCs. The pulsation analysis focused on the identification of pulsation periods in nine RCB stars in the MCs. Two different methods, Fourier analysis and dominant period subtraction, were employed for this purpose. Periodic variations are apparent in these stars, and for the majority, a period of around 40 days (common in RCB stars, Lawson et al. 1990, 1994) was detected using the second identification method. In the future, frequent data collection over several years, and more sophisticated pulsation identification techniques, will increase the probability of extracting individual periods from the complex RCB light curves.

We report the discovery of a stellar overdensity 8 degrees north of the centre of the Small Magellanic Cloud (SMC; Small Magellanic Cloud Northern Over-Density; SMCNOD), using data from the first 2 yr of the Dark Energy Survey (DES) and the first year of the MAGellanic SatelLITEs Survey (MagLiteS). The SMCNOD is indistinguishable in age, metallicity and distance from the nearby SMC stars, being primarily composed of intermediate-age stars (6 Gyr, Z=0.001), with a small fraction of young stars (1 Gyr, Z=0.01). The SMCNOD has an elongated shape with an ellipticity of 0.6 and a size of similar to 6 degrees x 2 degrees. It has an absolute magnitude of M-V congruent to -7.7, r(h) = 2.1 kpc, and mu v(r < r(h)) = 31.2 mag arcsec(-2). We estimate a stellar mass of similar to 10(5) M-circle dot, following a Kroupa mass function. The SMCNOD was probably removed from the SMC disc by tidal stripping, since it is located near the head of the Magellanic Stream, and the literature indicates likely recent Large Magellanic Cloud-SMC encounters. This scenario is supported by the lack of significant H-1 gas. Other potential scenarios for the SMCNOD origin are a transient overdensity within the SMC tidal radius or a primordial SMC satellite in advanced stage of disruption.

No description available.

This thesis presents the initiation of a multi-site photometric programme to examine the extraordinary behaviour displayed by 18 R Coronae Borealis (RCB) stars in the Magellanic Clouds (MCs). RCB stars exhibit a unique variability whereby they undergo rapid declines of up to several magnitudes. The decline may take several weeks, whereas the recovery to maximum light may take months or even years. The accepted wisdom for the cause of these enigmatic declines is a phenomenon whereby dust formed in the stellar environment reduces the brightness by as much as eight magnitudes (Clayton 1996). This is followed by the recovery phase during which the dust becomes homogeneously distributed in the stellar environment. The monitoring programme comprised the collection of UBVRI photometric data using five telescopes located at three different southern hemisphere longitudes (Las Campanas Observatory in Chile, Mount John University Observatory (MJUO) in New Zealand and the Southern African Large Telescope (SALT) in South Africa). The Optical Gravitational Lensing Experiment (OGLE), that operates at Las Campanas Observatory, provided the longest extent of data (December 1994 to February 2008). This was supplemented by data collected with telescopes at MJUO (September 2007 to January 2008) and SALTICAM on SALT (October 2007 to February 2008). Data calibration across the five instruments was a key element of the analysis, and entailed the use of F116 (an F region standard star) and other tertiary standards. Two important RCB characteristics, the enigmatic declines and the pulsational variability, form the bulk of the analysis presented in this thesis. Examination of the data acquired in the V and I filters resulted in the identification of a total of 18 RCB declines occurring in four stars (three stars in the Large Magellanic Cloud (LMC) and one in the Small Magellanic Cloud (SMC)). Construction of colour-magnitude diagrams (V −I vs V ), during the recovery to maximum light were undertaken in order to study the unique colour behaviour associated with the RCB declines. The combined recovery slope for the four stars was determined to be [(delta V)/(delta(V −I))] = 3.37 ± 0.24, which is similar to the value of [(delta V)/(delta(V −I))] = 3.1 ± 0.1 calculated for galactic RCB stars (Skuljan et al. 2003). In addition, the slopes calculated for the stars in the LMC ([(delta V)/(delta(V −I))]LMC = 3.34 ± 0.21) and SMC ([(delta V)/(delta((V −I))]SMC = 3.21 ± 0.22) alone, also agree to within their uncertainty. These results may imply that the nature of the dust (i.e. the particle size) is similar in both our Galaxy and the MCs. The pulsation analysis focused on the identification of pulsation periods in nine RCB stars in the MCs. Two different methods, Fourier analysis and dominant period subtraction, were employed for this purpose. Periodic variations are apparent in these stars, and for the majority, a period of around 40 days (common in RCB stars, Lawson et al. 1990, 1994) was detected using the second identification method. In the future, frequent data collection over several years, and more sophisticated pulsation identification techniques, will increase the probability of extracting individual periods from the complex RCB light curves.

Thesis (Ph. D.)--University of Sydney, 2001. / Includes tables. Title from title screen (viewed Apr. 22, 2008). Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the School of Physics, Faculty of Science. Degree awarded 2001; thesis submitted 2000. Includes bibliography. Also available in print form.

Thesis (Ph. D.)--University of Washington, 1998. / Vita. Includes bibliographic references (p. [231]-235).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1970. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1971. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 125-126).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1984. / Typescript. Vita. Includes tables. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.