The kinematic signature of the Galactic warp in Gaia DR1 - I. The Hipparcos subsample E. Poggio, R. Drimmel, R. L. Smart, A. Spagna and M. G. Lattanzi A&A, 601 (2017) A115 Published online: 15 May 2017 DOI: 10.1051/0004-6361/201629916