Exploring the nature of new main-belt comets with the 10.4 m GTC telescope: (300163) 2006 VW139 J. Licandro, F. Moreno, J. de León, G. P. Tozzi, L. M. Lara and A. Cabrera-Lavers A&A, 550 (2013) A17 Published online: 18 January 2013 DOI: 10.1051/0004-6361/201220080