Poster Presentation

Photopolarimetric Observation and Period Analysis of the UXor Type Young Star GM Cep

Po-Chieh Huang(IANCU) Chang-Yao Chen(Department of Physics, National Central University, Taiwan) Chia-Ling Hu(Taipei Astronomical Museum) Wen-Ping Chen(IANCU;Department of Physics, National Central University, Taiwan)

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 clumps. GM Cep is a UXOR in the young (~4 Myr) open cluster Trumper 37 at ~900 pc, showing prominent infrared access, H-alpha emission, polarization, abrupt brightness variation. Here we present multi-color photometric monitoring from 2009 to 2014 to add to decipher the century-long photometric behavior of this elusive young object. We reaffirm the study of Chen et al. (2012) that GM Cep showed (i) sporadic brightening on a time scale of days due to young stellar accretion, (ii) normal dust reddening as the star became redder when dimmer, (iii) the unusual “blueing” phenomena near the brightness minima when the star appeared bluer when dimmer, (iv) occultation events, each lasting for a couple months, with a probable recurrence time of about two years. The occultation events may be caused by a dust density inhomogeneity that signifies grain growth in a young stellar disk toward formation of planetesimals. Dynamical periodogram analysis suggests a possible period drift of the occultation events. The young star is moderately polarized, at 5.6% to 8.6% in the g band, 5% to 8% in the r band, and 4.0% to 6.9% in the i band, with a possible correlation of the level of polarization with the phase of the light curves.