Evans, Christopher John; (2001) Hot stars in the small Magellanic Cloud. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The relative proximity and reduced metallicity of the Magellanic Clouds permit observations of resolved stellar populations in different environments to the Galaxy. The primary dataset in this thesis is a spectroscopic survey of the hot-star population of the SMC obtained using the 2dF instrument. The survey comprises 4054 intermediate-resolution blue spectra which have been classified in the MK system. Measured H? equivalent widths are used to define luminosity types for the sample; however, when considered in terms of magnitude, the 2dF equivalent widths are found to be inconsistent with the published calibrations. The observed H-R diagram from the 2dF sample is used, in comparison with population synthesis models, to investigate the field-star IMF for the SMC, with the result that the most likely value for the slope of the IMF is F = -3.8 0.4. To permit the comparison between observed and synthesized models an effective temperature calibration as a function of spectral type is required. For O and B-type stars previously published values are used. However, when later type stars are classified in the MK system, the published calibrations are not appropriate because of the lower metal abundance. The results from model atmosphere calculations are used to refine the temperature scale for late-type stars so that it is applicable to the SMC. In addition, a detailed discussion of the selection effects in the observed sample is presented. These effects are then incorporated in the synthesis code so that the model population is subject to the same constraints as the observed sample. A separate dataset of high-resolution echelle spectra of 22 SMC 0-type stars is also presented. Newly observed morphological features are discussed and the spectra are then analysed using the non-LTE model atmosphere code TLUSTY to derive intrinsic stellar parameters for the sample.

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