We present the results of a J, H, and K_s photometric monitoring campaign of
a 0.72 x 6 sq deg. area centered on the Chamaeleon I star forming region. Data
were obtained on 15 separate nights over a 4 month time interval using the
2MASS South telescope. Out of a total of 34,539 sources brighter than the
photometric completeness limits (J=16.0, H=15.2, 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 deg 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 8 brown dwarf
candidates, have been identified based on variability and/or near-infrared
excess emission in the J-H vs. 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.Comment: To appear in AJ; see
http://www.astro.caltech.edu/~jmc/variables/cham1
