A 3μm survey of the Chamaeleon I dark cloud

We describe an L-band photometric survey of similar to 0.5 deg(2) of the Chamaeleon I dark cloud. The survey has a completeness limit of L < 11.0. Our survey detects 124 sources, including all known pre-K 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(H alpha) and K - L. Stars with K - L less than or equal to 0.6 have weak H alpha emission; stars with K - L greater than or equal to 0.6 have strong H alpha 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.