Constraining MOND using the vertical motion of stars in the solar neighbourhood

Stars with a different vertical motion relative to the Galactic disc have a different average acceleration. According to modified Newtonian dynamics (MOND) theories, they should therefore have a different average orbital velocity while revolving around the Milky Way. We show that this property can be used to constrain MOND theories by studying stars in the local neighbourhood. With the Hipparcos (Perryman et al. 1997) data set we can only place marginal constraints. However, the forthcoming Gaia (Perryman et al. 2001) catalogue with its significantly fainter cutoff should allow placing a stringent constraint.