The gravitational torque of bars in optically unbarred and barred galaxies D. L. Block, I. Puerari, J. H. Knapen, B. G. Elmegreen, R. Buta, S. Stedman and D. M. Elmegreen A&A, 375 3 (2001) 761-769 Published online: 15 September 2001 DOI: 10.1051/0004-6361:20010775