A Three Micron Survey of the Chamaeleon I Dark Cloud

We describe an L-band photometric survey of ∼ 0.5 deg2 of the Cha I dark cloud. The survey has a completeness limit of L < 11.0. Our survey detects 124 sources, including all known pre-main sequence stars with L ≤ 11. The fraction of sources with near-IR excess emission is 58% ± 4% for K = 9–11. Cha I sources have bluer H −K and K − L colors than pre-main sequence stars in Taurus-Auriga. These sources also have a strong correlation between EW(Hα) and K − L. Stars with K − L ≤ 0.6 have weak Hα emission; stars with K − L ≥ 0.6 have strong Hα emission. Because many Cha I sources are heavily reddened, this division between weak emission T Tauri stars and classical T Tauri stars occurs at a redder K − L than in Taurus-Auriga. Subject headings: ISM: individual (Chamaeleon I) — stars: formation — stars: premain sequence — infrared: stars Based on observations obtained with the SPIREX/Abu system in Antarctica. SPIREX/Abu operated for the 1999 observing season under agreement between the National Optical Astronomy Observatories (NOAO) and the Center for Astrophysical Research in Antarctica (CARA).