Testing the comet nature of main belt comets. The spectra of 133P/Elst-Pizarro and 176P/LINEAR J. Licandro, H. Campins, G. P. Tozzi, J. de León, N. Pinilla-Alonso, H. Boehnhardt and O. R. Hainaut A&A, 532 (2011) A65 Published online: 22 July 2011 DOI: 10.1051/0004-6361/201117018