  We report on the spectroscopic study of 19 low luminosity Flat Radio Spectrum
(LL FRS) sources selected from Marcha's et al. (1996) 200 mJy sample. In the
optical, these objects are mainly dominated by the host galaxy starlight. After
correcting the data for this effect, we obtain a new set of spectra clearly
displaying weak emission lines; such features carry valuable information
concerning the excitation mechanisms at work in the nuclear regions of LL FRS
sources. We have used a special routine to model the spectra and assess the
intensities and velocities of the emission lines; we have analyzed the results
in terms of diagnostic diagrams. Our analysis shows that 79% of the studied
objects harbour a Low Ionization Nuclear Emission-line Region (or LINER) whose
contribution was swamped by the host galaxy starlight. The remaining objects
display a higher ionization spectrum, more typical of Seyferts; due to the poor
quality of the spectra, it was not possible to identify any possible large
Balmer components. The fact that we observe a LINER-type spectrum in LL FRS
sources supports the idea that some of these objects could be undergoing an
ADAF phase; in addition, such a low ionization emission-line spectrum is in
agreement with the black hole mass values and sub-Eddington accretion rates
published for some FRS sources.
