Exploring pre-main-sequence variables of the ONC: the new variables

Abstract

Since 2004, we have been engaged in a long-term observing program to monitor\nyoung stellar objects in the Orion Nebula Cluster. We have collected about two\nthousands frames in V, R, and I broad-band filters on more than two hundred\nnights distributed over five consecutive observing seasons. The high-quality\nand time-extended photometric data give us an opportunity to address various\nphenomena associated with young stars. The prime motivations of this project\nare i) to explore various manifestations of stellar magnetic activity in very\nyoung low-mass stars; ii) to search for new pre-main sequence eclipsing\nbinaries; and iii) to look for any EXor and FUor like transient activities\nassociated with YSOs. Since this is the first paper on this program, we give a\ndetailed description of the science drivers, the observation and the data\nreduction strategies as well. In addition to these, we also present a large\nnumber of new periodic variables detected from our first five years of\ntime-series photometric data. Our study reveals that about 72% of CTTS in our\nFoV are periodic, whereas, the percentage of periodic WTTS is just 32%. This\nindicates that inhomogeneities patterns on the surface of CTTS of the ONC stars\nare much more stable than on WTTS. From our multi-year monitoring campaign we\nfound that the photometric surveys based on single-season are incapable of\nidentifying all periodic variables. And any study on evolution of angular\nmomentum based on single-season surveys must be carried out with caution.\n