Abstract Title: * Photometric monitoring of UX Ori type stars GM Cep and V1180 Cas Authors: * Asen Mutafov, Evgeni Semkov, Stoyanka Peneva, Sunay Ibryamov Institution: * IA and NAO Preferred format: * poster presentation Abstract Text: * Results from BVRI long-term photometric observations of the pre-main sequence stars GM Cep and V1180 Cas are reported. The two stars were originally classified as eruptive variables from EX Lupi type. But the precise analysis of photometric data accumulated over the year’s shows that they are certainly UX Orionis-type variables. Both types of pre-main sequence stars show variability with large amplitudes, but as in the case of EX Lupi stars variability is dominated of non-periodic outbursts, in the case of UX Orion stars long eclipses from circumstellar matter are observed. The analysis of the collected multicolor photometric data indicates the typical of UX Ori variables a color reversal during the minimums in brightness. This, along with the observed deep decreases in brightness, shows that stars are obscured by dust clumps or filaments passing through the line of sight to the stars. Photometric data presented in this poster show the usefulness of systematically monitoring of pre-main sequence stars with large amplitude variability. With the accumulation of enough photometric data, we can more accurately determine the causes of photometric variability of young stellar objects.