The needle in the haystack: where to look for more isolated cooling neutron stars (Corrigendum) B. Posselt, S. B. Popov, F. Haberl, J. Trümper, R. Turolla, R. Neuhäuser and P. A. Boldin A&A, 512 (2010) C2 Published online: 09 April 2010 DOI: 10.1051/0004-6361:20078430e