Photometric monitoring of PMS stars with the telescopes at Rozhen Observatory

For several decades we have been performing photometric monitoring of some of the star formation regions. Significant place in our program take observations of objects of the type FU Orionis, EX Lupi, UX Orionis and other similar but unclassified objects. These three types of young variable objects show changes in brightness with large amplitudes and attract the attention of star formation researchers. But it is not always possible to distinguish them from each other without the presence of long-term multicolor photometric data. For this reason, we collect data from current CCD observations and supplement them with data from the photographic plates archives. In this paper, we show the latest data from optical photometric studies of four PMS objects (V2493 Cyg, V582 Aur, V733 Cep and V1180 Tau) made at the Rozhen Observatory. Our monitoring is carried out in BVRI filters, which allows studying the variability in color indexes also. By analysis the historical light curves of these objects we are trying to obtain information about the processes associated with the early stages of stellar evolution.