Measurements of stellar spectra using a silicon photodiode array

Abstract

This work describes the preparation and use of the Plessey linear photodiode array in the observation of some stellar spectral features. An outline of the principles of the construction and operation of the diode array, along with some preliminary laboratory test results, form the initial part of this thesis. A suitable xy-movement control was designed and constructed, as well as the cryostat which was used to house the array at the coude focus of the telescope. Constraints at the telescope imposed several limitations, all of which had to be taken into consideration. The general experimental operation, signal processing, and control logic are all described, along with the data acquisition and storage techniques. Data reduction and analysis methods were developed to deal with difficulties peculiar to this type of photodiode array system. A theoretical investigation into the effects of the array geometry on the collection of spectra is described. On the astronomical side, observations of the neutral oxygen triplet at A7774 form the major set of results obtained. The equivalent width of A7774 can give information about the temperature absolute magnitude, and luminosity of many types of stars. The role of non-LTE is discussed, as well as its effect on the measurements of line widths. Finally, the phenomenon of stellar mass loss is outlined. Unfortunately, few results were obtained in this investigation. However, a description of the reasons behind the loss of matter from stars is given, along with probable mass loss mechanisms, features, and detection. A brief word on mass loss rates is included, but the lack of sufficient results in this region pre-empted any quantitative comparisons.