Hipparcos photometry of 24 variable massive stars (α Cygni variables) F. van Leeuwen, A. M. van Genderen and I. Zegelaar Astron. Astrophys. Suppl. Ser., 128 1 (1998) 117-129 Published online: 15 February 1998 DOI: 10.1051/aas:1998129