Impact of basic angle variations on the parallax zero point for a scanning astrometric satellite Alexey G. Butkevich, Sergei A. Klioner, Lennart Lindegren, David Hobbs and Floor van Leeuwen A&A, 603 (2017) A45 Published online: 05 July 2017 DOI: 10.1051/0004-6361/201730781