R. Williams’s research while affiliated with Paris Diderot University and other places

Results of a five-month campaign of optical monitoring the Seyfert 1 galaxy NGC 4593 are presented. High resolution H-alpha and H-Beta spectra and direct images in the Johnson U, B, V, R, and I bands were obtained between January and June 1990. The emission lines and the continuum showed strong variations on time scales of weeks to days. The H-alpha line varied by more than 30% within only 5 days. Cross-correlating the light curves of the Balmer lines with that of the optical continuum gives a lag of around 4 days. Therefore, this low luminosity Seyfert galaxy may have one of the smallest broad line regions (BLRs) known so far.

We present results of a five month spectroscopic monitoring campaign of the Seyfert-1 galaxy NGC 3516. Using a new calibration method and applying a correction for seeing differences during the various observations we can scale the spectra to each other with a much higher accuracy than hitherto achieved. NGC 3516 shows large amplitude variations on a time scale of several weeks. Asymmetric profile variations occur on the same time scale as the continuum variations. We show the presence of a varying dip on the blue wing of the H-beta profile, which is not present on the H-alpha profile, and which corresponds to the absorption features previously seen in the UV emission lines of NGC 3516. From cross-correlation analysis we find a time lag of 14 +/- 2 days for the H-alpha and 7 +/- 3 days for the H-beta emission-line response to continuum variations.