Probing M subdwarf metallicity with an esdK5+esdM5.5 binary Ya. V. Pavlenko, Z. H. Zhang, M. C. Gálvez-Ortiz, I. O. Kushniruk and H. R. A. Jones A&A, 582 (2015) A92 Published online: 15 October 2015 DOI: 10.1051/0004-6361/201526810