Chemically Decoupled Nuclei in the Spiral Galaxies NGC 4216 and NGC 4501

By using bidimensional spectral data obtained at the 6m telescope for theVirgo spirals NGC 4216 and NGC 4501, we have found chemically distinctmetal-rich nuclei in these galaxies. Under the assumption of equal ages for thenuclear and bulge stellar populations, the metallicity difference between thenuclei and their environments in the galaxies is estimated as a factor of 2.But we have also found an age difference between the nucleus and the bulge inNGC 4216: age-metallicity disentangling on the diagrams (H-beta, Mgb), (H-beta,[MgFe]), and (H-beta, $$) results in an age estimate for the nucleus of 8 -12 billion years, the bulge being older by a factor of 1.5 - 2; and theself-consistent metallicity difference estimate is then a factor of 3. Thesolar magnesium-to-iron ratios in the galactic nuclei show evidence for a longduration of the secondary nuclear star formation bursts which produced thechemically distinct stellar subsystems. Detailed morphological and kinematicalanalyses made for the stellar and gaseous structures in the centers of NGC 4216and 4501 have revealed the presence of circumnuclear stellar-gaseous disks withradius of some hundreds parsecs which demonstrate fast axisymmetric rotationand lie exactly in the planes of the main galactic disks.Comment: 28 pages, Latex uses aasms4.sty, 17 Postscript figures, accepted by A