An investigation of the micro-variations of highly luminous OBA type stars .I.

Photometric observations of eight OBA stars of absolute bolometric magnitude brighter than -7 mag, obtained during the Walraven five-color simultaneous VBLUW photometer with a 16-arcsec aperture on the 90-cm Dutch Light Collector at ESO since 1980 are reported. The data-reduction procedures are explained; the stability of the comparison stars is characterized; and the data are presented in tables and graphs. Brightness variations of 0.01-0.1 mag on time scales of days or weeks are observed in all eight objects, the mean error of the nightly averages being about + or - 0.002 mag, and a secular decrease of 0.012 mag over about 2 yr is found for HD 37022. The larger variations seen in the B-U color indices of some of the stars are attributed to short-period (days or less) variations in temperature and/or density near the stellar surfaces.