Margarida Serote Roos
Centro de Astronomia e Astrofísica da Universidade de Lisboa

We have studied the stellar populations present in a sample of low luminosity BL Lac type objects (Marchã et al., 1996, 281, 425). Selected with the primary objective of studying the differences between BL Lacs and their closest relatives, the sample studied by Marchã et al. contains 55 optically bright, low luminosity core dominated radio sources. In order to study the properties of these objects and since they are of low luminosity, the contribution of the host galaxy is quite important and can not be underestimated. Hence, a reliable method to search for the stellar population is required.
We make use of the initial spectroscopic information to obtain the stellar popu-lations of the sample. We use the population synthesis method, with a stellar data base. The mathematical method used, developed by D. Pelat (1997, MNRAS 284, 365), gives a unique solution, the principal minimum, and is independent of the initial parameters. It has also small sensitivity to observational errors.
We will present our results for 19 objects of the sample and will show how the emission spectra appear once the stellar populations have been subtracted from the original spectra, putting in evidence "hidden" AGN.

Grupo de Astronomia da Universidade da Madeira - 2001