Strömgren photometry of the open clusters NGC 6134 and NGC 3680 H. Bruntt, S. Frandsen, H. Kjeldsen and M. I. Andersen Astron. Astrophys. Suppl. Ser., 140 2 (1999) 135-143 Published online: 15 December 1999 DOI: 10.1051/aas:1999412