We present Hubble Space Telescope blue spectra at intermediate spectral resolution for the nuclei of 23 nearby disk galaxies .
These objects were selected to have nebular emission in their nuclei , and span a range of emission-line classifications as well as Hubble types .
In this paper we focus on the stellar population as revealed by the continuum spectral energy distribution measured within the central 0 \farcs 13 ( \sim 8 pc ) of these galaxies .
The data were modeled with linear combinations of single-age stellar population synthesis models .
The large majority ( \sim 80 % ) of the surveyed nuclei have spectra whose features are consistent with a predominantly old ( \gtrsim 5 \times 10 ^ { 9 } yr ) stellar population .
Approximately 25 % of these nuclei show evidence of a component with age younger than 1 Gyr , with the incidence of these stars related to the nebular classification .
Successful model fits imply an average reddening corresponding to A _ { V } \approx 0.4 mag and a stellar metallicity of ( 1–2.5 ) Z _ { \odot } .
We discuss the implications of these results for the understanding of the star formation history in the environment of quiescent and active supermassive black holes .
Our findings reinforce the picture wherein Seyfert nuclei and the majority of low-ionization nuclear emission-line regions ( LINERs ) are predominantly accretion-powered , and suggest that much of the central star formation in H ii nuclei is actually circumnuclear .