We have used a sample of 90 Seyfert 2 and 87 LINER galaxies to study the abundance of the emitting gas by comparing the optical emission-line ratios with photoionization model values. We have shown that the range of values presented by [N II] / H and [S II] / H can only be reproduced by varying the N and S abundances with respect to the other heavy elements, from 0.5 to 5 times solar. We have also shown that the N and S abundances seem to be correlated, because we can only reproduce the [N II] / H x [S II] / H diagram by varying together the abundances of these elements.
We also show that when the observed regions have diameters smaller than 500 pc, most Seyfert 2's and LINERs present an overabundance of sulfur at the nuclei. On the basis of this result and a similar one previously obtained for the nitrogen abundance, it seems that an overabundance of nitrogen and sulfur in a small region centered on the nucleus (500-1000 pc) is a common property of most Seyfert 2's and LINERs.
We would like to thank H. Schmit for valuable help in constructing the tables and graphs used in this work and Dr. G. Ferland for kindly sending his program CLOUDY, used in the model calculations. This work was partially supported by the Brazilian institutions Fundacao de Amparo a Pesquisa do Estado do Rio Grande do Sul (FAPERGS), Financiadora de Estudos e Projetos (FINEP), and Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq).