List of Variable objects in the Orion nebula

After a careful quality control more than 13000 light curves were produced in either R or I; the total number of matched light curves is 11889. The corresponding stars were subsequently matched with the 2MASS point source catalog, resulting in 8197 stars with I<16.5mag and AAA quality flags. We employed three methods-amplitude, standard deviation, and Stetson J-index - to identify variable objects in our sample, successfully classifying 561 stars as variables (irregular, periodic, and quasi-periodic).

These stars serve as the foundation for further analysis. We confirmed 456 of these as known pre-main sequence stars through cross-referencing with existing young stellar object catalogs, supported by spectroscopic and photometric data. The youth of the remaining stars was established based on their optical and infrared color signatures.

The period P could be determined for 147 sources and ranges from 0.2 days to several weeks. The frequency of very short periods (<1day) is 2 to 4 times higher than reported in previous studies. A significant population (10%) comes primarily from Weak-line T Tauri stars, which are characterized by rotation periods of less than 1 day.

These results emphasize the advantages of observations with an exceptional time sampling strategy that allows the identification of variability on scales from hours to years.