GALAXY PROPERTIES IN DIFFERENT ENVIRONMENTS .2. STAR-FORMATION IN BULGES OF LATE-TYPE SPIRALS

The star formation history in the nucleus of late spiral galaxies is c ompared between a sample in a high galaxy density medium (HDS) and a c ontrol sample (CS) of isolated galaxies. We have observed 20 HDS and 1 8 CS galaxies from a larger list generated by the application of a gro up-finding algorithm to the SSRS survey. Using equivalent widths of ab sorption lines and the continuum distribution, we determined the nucle ar stellar population types, from those dominated by old population to those containing star formation bursts of different ages and intensit ies. The HDS and CS stellar population type histograms are similar, su ggesting that environmental influences, at least for the present sampl e, do not affect substantially the nuclear stellar population. However , the nuclear emission lines indicate that, in the BPT diagnostic diag rams, there is an excess of HDS galaxies located within or close to th e AGN loci. For six HDS and two CS galaxies, it was possible to determ ine oxygen (O/H) and nitrogen (N/H) abundances. The samples present si milar O/H values, but in the CS galaxies the N/O ratio is lower at equ al galaxy luminosity.