ON THE POSSIBLE VARIABILITY OF THE MAIN-SEQUENCE A-STAR THETA-VIRGINIS AND 109-VIRGINIS

Differential Stromgren uvby photometric observations from the Four Col lege Automated Photoelectric Telescope are used to examine the possibl e variability of the spectrophotometric standards theta Vir and 109 Vi r. No evidence is found for variability within a season of observation . Small year to year differences are most likely due to unaccounted fo r extinction changes.