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Published online by Cambridge University Press: 12 April 2016
UBV(RI)c photoelectric observations of four variable magnetic Bp stars (HD 21699, HD 177003, HD 184927 and HD 217833) were carried out between 1989 and 1992. Random fluctuation of 0m.1 range was detected in the U colour band in the case of HD 177003 and HD 184927. The U light curve of HD 21699 shows 0m.02 peaks superposed on the periodic light variation which definitely exceeds the typical error of the observations. It is not likely that atmospheric extinction or observational error would cause the phenomena described. On the other hand there are no physical processes known which lead to such changes of the U band continuum radiation in Bp stars.
Based on observations collected at the Konkoly Observatory