M-dwarf metallicities. A high-resolution spectroscopic study in the near infrared A. Önehag, U. Heiter, B. Gustafsson, N. Piskunov, B. Plez and A. Reiners A&A, 542 (2012) A33 Published online: 21 June 2012 DOI: 10.1051/0004-6361/201118101