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Title: A study of T Tauri stars with multiple spectral types and their surface temperatures
Author: Horrobin, Matthew
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2000
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This thesis describes the results of two spectral studies of T Tauri stars. T Tauri stars are young, low mass, stars which have yet to evolve to the point where Hydrogen fusion occurs in their cores. They are normally found in groups associated with gas clouds in locations called star forming regions. Much work has been done to explain the bizarre spectral features of T Tauri stars, and this has led to the development of a standard model for their structures. Classical T Tauri stars are thought to be surrounded by large discs of accreting material, which slowly adds to the mass of the star. This accretion process results in large U.V. and I.R. fluxes for the stars when compared to their main sequence counterparts. Weak-line T Tauri stars do not display any accretion features and are thought to be more evolved than Classical T Tauri stars. Observations show that both types of T Tauri star have active chromospheres and large cool spots, which are both thought to be a result of strong magnetic fields. This thesis is motivated by two studies, one spectroscopic, one photometric, both of which suggest that some T Tauri stars display photospheric features from regions of different temperatures, or multiple spectral types (MST). The first spectral study discussed is of near-I.R. data taken with UKIRT. The spectra are of high resolution data from the region around 1.63 mm, and are of T Tauri, giant and dwarf stars of known spectral type. It is shown that a ratio of selected OH to Fe lines gives a good trend with the optically measured Teff, derived from spectral types, for both dwarfs and giants. Whilst some of the T Tauri stars fit this trend, it is found that 4 stars clearly lie above it. This is taken as an induction of cooler regions in the spectra than had previously been detected, an MST effect. The second spectral study discussed is of optical data taken with the FLAIR system on the UKST. The spectra span the entire optical region observable with this instrument, and are intended to show variation in temperature sensitive features between the blue and red optical regions. Spectra are presented from 2 consecutive nights of observations and previously discovered MST stars are found to show deeper G bands than would be predicted from the TiO bands in the red spectra. It is found that the G band of one object has varied both on a night to night basis and since the previous observations from the mid-1980's. It is also shown that no variation has occurred in the red spectra.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available