A Spectroscopic Study Into Accretion In Herbig Ae/Be Stars

This thesis presents a spectroscopic study of the stellar properties, accretion rates, and emission lines of 91 Herbig Ae/Be stars.
Medium resolution spectra and optical photometry are used to spectrally type a sample of 91 Herbig Ae/Be stars in a homogeneous fashion. Stellar parameters of temperature, surface gravity, mass, radius, luminosity, distance, age, and reddening are determined using the above in combination with pre-main sequence tracks. The temperatures are in agreement with previous assessments, while new distance and mass estimates for some objects constitute a large improvement.
Measurements of the UV-excess across the Balmer jump region are made, and they are modelled within the context of magnetospheric accretion. Accretion rates are derived from the fitting. Seven Herbig Be stars could not be fitted within this context, suggesting a possible breakdown of magnetospheric accretion towards the higher mass Herbig Ae/Be stars. Different relationships between accretion rate and age are observed for the cases of Herbig Ae stars and Herbig Be stars; this is suspected to be an evolutionary effect of both the star approaching the main sequence and the pre-main sequence lifetime of the star itself.
Line luminosities are measured for 32 different emission lines ranging from 4000-21700 Angstrom. All lines are observed to be correlated with the accretion luminosity, providing multiple new accretion diagnostics. The mean power-law relationship between accretion luminosity and line luminosity is observed to be the same between HAeBes and CTTs, within the errors. However, a line by line comparison between the two, demonstrates deviation in 80% of comparable lines. This deviation appears greatest in the Herbig Be regime. Further investigation is required into the line profiles and current scatter observed in relationships for different classes of pre-main sequence stars.