On the nature of optical nuclei in FR I radio-galaxies from ACS/HST imaging polarimetry A. Capetti, D. J. Axon, M. Chiaberge, W. B. Sparks, F. Duccio Macchetto, M. Cracraft and A. Celotti A&A, 471 1 (2007) 137-149 Published online: 18 June 2007 DOI: 10.1051/0004-6361:20077370