Near-Infrared Photometric Variability of Stars toward the Chamaeleon I Molecular Cloud

We present the results of a J, H, and K_s photometric monitoring campaign of a 0.°72 × 6° area centered on the Chamaeleon I star-forming region. Data were obtained on 15 separate nights over a 4 month time interval using the Two Micron All Sky Survey south telescope. Out of a total of 34,539 sources brighter than the photometric completeness limits (J = 16.0, H = 15.2, and K_s = 14.8), 95 exhibit near-infrared variability in one or more bands. The variables can be grouped into a population of bright, red objects that are associated with the Chamaeleon I association and a population of faint, blue variables that are dispersed over the full 6° of the survey and are likely field stars or older pre–main-sequence stars unrelated to the present-day Chamaeleon I molecular cloud. Ten new candidate members of Chamaeleon I, including eight brown dwarf candidates, have been identified based on variability and/or near-infrared–excess emission in the J-H versus H-K_s color-color diagram. We also provide a compendium of astrometry and J, H, and K_s photometry for previously identified members and candidate members of Chamaeleon I