Hidden Spectra Treasures in the Foster Archive: A Pilot Study of the Be Stars a Eri, a Col, ? Car and ? Cen

We present the archive of spectroscopic photographic plates of the Universidad Catolica historic observatory Manuel Foster. The archive includes more than 4800 plates covering the period of time from 1928 to 1991. The spectra present in the archive are mostly those of bright variable or binary stars observed at different epochs. We developed a method of digitalization and data processing for the plates and verified it through the analysis of a selected sample of spectra. As an example of the potential relevance of this Foster archive we studied the variation of helium, H beta and H gamma spectral lines over time (1980-1991), complementing with high resolution spectroscopic data from the "Be Star Observation Survey " (2012-2015), of four Be stars mainly, alpha Eri, alpha Col, omega Car and eta Cen. The spectra of these stars show evidence of a circumstellar gas disk present in both periods of time. From the spectroscopic analysis, we found these stars are variable in helium and this variability presents an opposite behavior with the variability observed in the EW of the H beta line profile. This archive represents a unique source of data from past that is available for the use of the community.