A study of the long-term brightness and colour variations of the Be star 88 Herculis

Photometric observations of the Be star 88 Herculis from 12 different sources were collected covering a period from 1968 to 2019 for the purpose of studying variations on the timescale of years to decades. All the used data was either available in or transformed into the Johnson Standard system. Since systematic photometric observations began in the 1970's the star underwent three long-term variation cycles that differ in strength and length. A quantitative description of each cycle is given. The data suggests that the star is also changing on an even longer timescale in both luminosity and colour. The photometric data was compared to the evolution of the Hα emission line and discussed in connection to possible physical models. It is shown that he object exhibits behavior that corresponds to what is described in literature as the Negative correlation.