The Initial Mass Function and Young Brown Dwarf Candidates in NGC 2264. I. The Initial Mass Function around S Monocerotis

The young open cluster NGC 2264 was observed on 2002 January 6-7 with the CFH12K mosaic CCD on the 3.6 m Canada-France-Hawaii Telescope to investigate the shape of the initial mass function (IMF). In order to select the pre-main-sequence (PMS) members more completely, Chandra X-Ray Observatory archival data were retrieved and used for the identification of X-ray-emitting weak-line T Tauri stars. In addition, the (R - I, V - I) diagram was used to exclude background late-type giants, and a statistical approach was applied to estimate the number of contaminating foreground main-sequence stars. The shape of the IMF of the Chandra field of view is flat between log m = -0.4 and ∼- 1.0 (m in solar mass units), with a weak signature of a dip near log m = -0.2. The overall shape of the IMF is very similar to those obtained for the Pleiades or the Trapezium. The fraction of disked PMS stars, as noted by Rebull and coworkers, does not show any signature of mass dependency. The age of PMS stars between log m = 0 and -1 is 3.1 ± 0.5 Myr.

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