Spectroscopy and variability of Narrow Line Seyfert 1 galaxies

We present the results of several investigations into the nature of Narrow Line Seyfert 1 Galaxies (NLS1s). These investigations comprise optical spectroscopy, with particular attention paid to the Coronal Line Region (CLR), short term monitoring in the B band, and a search for optically thin gas in the Broad Line Region of AGN.;Optical spectra have been obtained for 19 NLS1s. A large database of spectral features is presented, including upper limits for coronal lines when 3 detections were not obtained. These will provide a valuable resource for testing models of the EUV continuum. There is some evidence of broad wings to H in NLS1s. The Narrow Line Region shows evidence of high electron temperatures and low electron densities. The Coronal Line Region consists of gas in a decelerating outflow. No simple relation between coronal line strengths and the ROSAT PSPC photon index is seen.;NLS1s do not show evidence of variability in the B band over timescales of 1 week. The B band continuum appears not to share a common origin with the highly variable soft X-ray flux.;The O I 8446 line is systematically narrower and more asymmetric than H in AGN generally. The difference in FWHM becomes more pronounced with decreasing line width. This indicates that optically thin gas is present in the BLR, and is a more important component of it in NLS1s, where it extends closer to the core of the line. These results favour models in which NLS1s are characterized by a relatively high accretion rate onto a relatively small black hole. They also imply the presence of a highly ionized, optically thin inner BLR and a less highly ionized, optically thick outer BLR. The strong soft excess in NLS1s causes the inner BLR to extend further outwards than in 'normal' Seyfert 1s.