A Spitzer View of the Young Open Cluster NGC 2264

TL;DR

This study uses Spitzer mid-infrared data to classify young stellar objects in NGC 2264, revealing spatial distributions, disk evolution stages, and the influence of massive stars on disk fractions.

Contribution

It introduces a normalized classification scheme for young stellar objects using multicolor photometry and compares it with SED slope-based classification, providing new insights into disk evolution.

Findings

Identified two subclusterings of Class I objects in the CONE region.

Discovered a high fraction of transition disks among solar-mass stars.

Found a low primordial disk fraction near the massive star S Mon, increasing with distance.

Abstract

We have performed mid-IR photometry of the young open cluster NGC 2264 using the images obtained with the Spitzer Space Telescope IRAC and MIPS instruments and present a normalized classification scheme of young stellar objects in various color-color diagrams to make full use of the information from multicolor photometry. These results are compared with the classification scheme based on the slope of the spectral energy distribution (SED). From the spatial distributions of Class I and II stars, we have identified two subclusterings of Class I objects in the CONE region of Sung et al. The disked stars in the other star forming region S MON are mostly Class II objects. These three regions show a distinct difference in the fractional distribution of SED slopes as well as the mean value of SED slopes. The fraction of stars with primordial disks is nearly flat between log m = 0.2 -- -0.5, and that of transition disks is very high for solar mass stars. In addition, we have derived a somewhat higher value of the primordial disk fraction for NGC 2264 members located below the main pre-main sequence locus (so-called BMS stars). This result supports the idea that BMS stars are young stars with nearly edge-on disks. We have also found that the fraction of primordial disks is very low near the most massive star S Mon and increases with distance from S Mon.