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Observational Signatures of Convection in Solar Type Stars

Devon Hamilton

Doctor of Philosophy 2001
Graduate Department of Astronomy and Astrophysics, University of Toronto

In this thesis, a new technique for studying convection is developed using relative line-shifts. The technique is tested using the sun's visible flux spectrum and the most current FeI line positions available, and can be applied at significantly lower spectral resolutions and signal-to-noise ratios than has been done previously. These line-shifts show a clear dependence on both line strength and wavelength. Similar observations in the solar intensity spectrum demonstrate that the effects of limb darkening on the line-shifts are relatively minor. Because the solar intensity spectrum has been observed well into the infrared, it has been used to study the line-shift techniques over the broadest possible spectral region. The FeI line-core shift distributions show clear evidence of a dependence on line strength at all wavelengths, and sensitivities to wavelength are found at shorter wavelengths. Line-shifts for 1323 CO lines between 2.2 and 5.5 microns are also determined. Clear evidence of a dependence on line strength is found at all wavelengths, and interesting line-shift behavior is found when the excitation energy and quantum numbers of the CO transitions are examined. A similar study of CO and OH line-shifts is done using a sunspot umbral spectrum, and the convective motions are found to be greatly suppressed. Line-shifts are also examined in the infrared spectrum of six cool giant stars. The vigorous nature of convection seems to decline with Teff, which is consistent with expectations.

Reproduced with permission by Marlene Cummins library@astro.utoronto.ca
December 5 2001