Stellar populations in active galactic nuclei — I. The observations

Recent observations supported by theoretical models have led to the view that giant and supergiant stars are overabundant, and/or a high-metallicity component may be present, in the stellar populations at the centres of active galaxies. Here we attempt to quantify these effects by observing the strengths 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 spectroscopic data we are able to separate the stellar populations in and around the nucleus, 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 number of circumnuclear regions. Comparisons reveal gradients in both the reddening and the stellar population within the central regions of most galaxies. Detailed stellar population synthesis will be presented in a companion paper.