Po-Chieh Huang (Graduate Institute of Astronomy, National Central University, Taiwan), Chia-Ling Hu (Taipei Astronomical Museum, Taipei), Shuhrat Ehgamberdiev (Ulugh Beg Astronomical Institute, Uzbekistan), Otabek Burkhonov (Ulugh Beg Astronomical Inst
UX Orionis stars, or UXORs, are a sub-type of Herbig Ae/be or T Tauri stars exhibiting sporadic extinction of stellar light due to circumstellar dust obscuration. GM Cep is such a UXOR in the young (~4 Myr) open cluster Trumpler 37 at ~900 pc, showing prominent infrared access, H-alpha emission, and flare activity. Our multi-color photometric monitoring from 2009 to 2018 showed (i) sporadic brightening on a time scale of days due to young stellar accretion, (ii) cyclic, but not strictly periodical occultation events, each lasting for a couple months, with a probable recurrence time of a few years, (iii) normal dust reddening as the star became redder when dimmer, with unusual color behavior near the brightness minima when the star appeared bluer when dimmer (the “blueing” phenomenon), (iv) moderate polarization from 2% to 9% in g, r, and i bands. The occultation events may be caused by an orbiting dust clump, or a string of dust clumps along one of the spiral arms in the protoplanetary disk. In either case, the clumpy disk of GM Cep signifies the density inhomogeneity in a young stellar disk from grain coagulation to planetesimal formation. We will present quantitative analysis for the correlation between duration and level of extinction from observed occultation events, together with the discussion on the photopolarimetric behavior of GM Cep and comparison with typical UXOR variables.