Abstract
ABSTRACT We present optical spectra of the nuclei of seven luminous (P 178MHz >∼10 25 W Hz −1 Sr ) nearby (z < 0.08) radiogalaxies, which mostly correspond tothe FR II class. In two cases, Hydra A and 3C 285, the Balmer and λ4000˚A breakindices constrain the spectral types and luminosity classes of the stars involved, re-vealing that the blue spectra are dominated by blue supergiant and/or giant stars.The ages derived for the last burst of star formation in Hydra A are between 7 and40 Myr, and in 3C 285 about 10 Myr. The rest of the narrow-line radiogalaxies (four)have λ4000˚A break and metallic indices consistent with those of ellipt ical galaxies.The only broad-line radiogalaxy in our sample, 3C 382, has a strong featureless bluecontinuum and broad emission lines that dilute the underlying blue stellar spectra.We are able to detect the Ca II triplet in absorption in the seven objects, with goodquality data for only four of them. The strengths of the absorptions are similar tothose found in normal elliptical galaxies, but these values are both consistent withsingle stellar populations of ages as derived from the Balmer absorption and breakstrengths, and, also, with mixed young+old populations.Key words: galaxies: active – galaxies: starbursts – galaxies: stellar content
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