The observations were performed at different sites as listed in Table2 (click here). All telescopes were equipped with a photomultiplier, and photometer apertures larger than 20'' were used. The integration time (> 10 s) was chosen such that each data point is only limited by scintillation and not by photon noise (Young 1967). For most programme stars we have used two comparison stars (observed typically every 5 min) to correct for atmospheric and instrumental effects. The sky background was measured at least once each hour. Most, but not all of the stars were measured in Strömgren v and b. The date and duration of the observations, and the number of data points for each programme star are listed in Table1 (click here).
Table 2: Sites, observers and used telescopes for our survey