Looking for obscured QSOs in the X-ray emitting ERO population P. Severgnini, R. Della Ceca, V. Braito, P. Saracco, M. Longhetti, R. Bender, N. Drory, G. Feulner, U. Hopp, F. Mannucci and C. Maraston A&A, 431 1 (2005) 87-95 Published online: 02 February 2005 DOI: 10.1051/0004-6361:20041587