The initial mass function and young brown dwarf candidates in NGC 2264. III. Photometric data

摘要

We have performed deep wide-field CCD photometry of the young open cluster NGC 2264 to study the extent of star-forming regions (SFRs) and the shape of the initial mass function. In this paper, we present VRI and Ha photometry for more than 67,000 stars. From the spatial distribution of the selected Ha emission stars, we identify two active SFRs and a less active halo region surrounding these two SFRs. There are several Ha emission stars in the field region outside the halo region, and these may be newly formed stars in the Mon OB1 association surrounding the cluster. The locus of pre-main-sequence (PMS) stars in the I-C versus V-I-C diagram is revised from the distribution of Ha and X-ray emission stars in the diagram. The mean reddening of late-type PMS stars is estimated to be E(B-V) approximate to 0.2 mag using the distribution of X-ray emission stars in the 2MASS color-color diagram. We can confirm that the Ha emission stars below the PMS locus (so-called BMS stars) are bona-fide members of NGC 2264 from their spatial distribution as well as from their near-IR excess in the 2MASS color-color diagram. In addition, four objects around IRS-2 detected with the Spitzer IRAC are also classified as BMS stars.