Stellar populations in active galactic nuclei - I. The observations

Recent observations supported by theoretical models have led to the view th at giant and supergiant stars are overabundant, and/or a high-metallicity c omponent may be present, in the stellar populations at the centres of activ e galaxies. Here we attempt to quantify these effects by observing the stre ngths of the stellar absorption lines of Mg b, Na I and the Ca II triplet, as well as molecular bands such as CN and TiO. Using long-slit spectroscopi c data we are able to separate the stellar populations in and around the nu cleus, for a sample including normal, LINER, starburst and Seyfert galaxies . In this paper we present the data, namely spectra of the nucleus and of a n umber of circumnuclear regions. Comparisons reveal gradients in both the re ddening and the stellar population within the central regions of most galax ies. Detailed stellar population synthesis will be presented in a companion paper.