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We present optical long-slit spectra of the Virgo dwarf elliptical galaxy VCC510 at high spectral and spatial resolution. Heliocentric velocities andvelocity dispersions as functions of galaxy radius are derived by deconvolvingline-of-sight velocity distributions. A maximum rotation v_rot=8 km/s insidehalf the effective radius (re~20 arcsec) and a mean, radially flat velocitydispersion sigma=44 km/s are measured. The core extending over the inner 2arcsec (~140 pc) is found to rotate in the opposite sense with v_rot(core) ~-1/2 v_rot. VCC 510 (M_B ~ -15.7) is therefore by far the faintest and smallestgalaxy with a counter-rotating core known. From the main body rotation and thevelocity dispersion profile we deduce that VCC 510 is anisotropic and clearlynot entirely supported by rotation. By comparison of Lick absorption-lineindices with stellar population models we derive an old luminosity-weighted age(10 Gyr) and sub-solar metallicity ([Z/H]=-0.4) inside the effective radius.There is tentative evidence that the counter-rotating core might be younger andless alpha/Fe enhanced. From the stellar population parameters we obtain atotal stellar mass-to-light ratio of ~3.6 (M/L_B)_sun which is significantlylower than a rough dynamical estimate obtained from the kinematics through thevirial theorem (~15). This discrepancy hints toward the possible presence ofdark matter in the centre of VCC 510. We discuss the origin of thecounter-rotating core and exclude fly-by encounters as a viable possibility.Gas accretion or galaxy merging provide more likely explanations. VCC 510 istherefore the direct observational evidence that such processes do occur incluster satellite galaxies on dwarf galaxy scales.Comment: 4 pages, two figures, accepted by A&A Letter

A counter-rotating core in the dwarf elliptical galaxy VCC 510