Circumstellar Disk Candidates Identified in NGC 2264

Abstract

We present an optical and near-infrared study of a 45 0 Â 45 0 field in NGC 2264, which includes both S Mon and the Cone Nebula. We report photometry at optical (UBVR C I C ) and near-infrared (JHK) wavelengths for $5600 stars and spectroscopic classifications for $400 of these stars. We identify circumstellar disk candidates using three techniques: excess ultraviolet (UÀV ) emission, excess near-IR (IÀK and HÀK) emission, and H emission-line equivalent widths for those stars with spectra. We find generally good correlation between disk indicators thought to originate from different physical processes. We find little if any evolution of disk fraction with stellar age or mass. However, when we derive mass accretion rates ( _ M M) from the excess emission at U, we find that _ M M decreases with age over the age range spanned by our data, $0.1-5 Myr, and increases with mass over the range $0.25-1 M . These findings are comparable to results found previously by us in the Orion Nebula cluster flanking fields.

Stellar models simulating the disk-locking mechanism and the evolutionary history of the Orion Nebula cluster and NGC 2264

“…These IRAC data were obtained in two epochs, March and October 2004, and can help us to distinguish the stars with a disk from diskless objects. In addition, we investigated W λ (Hα), U − V and near-infrared excesses (I − K and H − K) by Rebull et al (2002), near-infrared excess and W λ (Hα) by Dahm & Simon (2005), mid-infrared excess by Cieza & Baliber (2007), and uband exccess by Venuti et al (2014). For disk identification purposes, we used the following values to indicate the presence of a disk: .15, [3.8 − 8.0] ≥ 0.7, and α IRAC > −2.56.…”

“…Rebull et al (2000) described the origin of some disk indicators commonly used in the literature, such as U − V excess, Hα emission (which are accretion diagnostics and, consequently, indicate the presence of circumstellar disks), and infrared excesses (I − K and H − K, which are diagnostics of dust heated in circumstellar disk). Rebull et al (2002) used U − V, I − K, H − K excesses, and Hα emission to identify circumstellar disk candidates in NGC 2264. Makidon et al (2004) used these same disk indicators to search for eventual correlations with period of NGC 2246 stars, but found no conclusive evidence that slower rotating stars have disk indicators, or that faster rotators are less likely to have disk indicators.…”

A deep, wide-field search for substellar members in NGC 2264

“…The study introduced here is only a small part (0.6 deg 2 ) of a much broader survey, which has mapped significant areas (70 deg 2 ) of a variety of environments (ages 1-600 Myr) sufficiently deeply to probe BD; in all of the targeted regions, the limiting mass is in the range 10-40 M Jup . NGC 2264, because of its youth and relative proximity (3 Myr, 760 pc; Lamm et al 2004;Rebull et al 2002;Sung et al 1997;Park et al 2000), is probed to the lower end of this mass range with the current observations. We will discuss our initial findings on NGC 2264 in Sect.…”

“…9. We note we have no objects in common with the sample of Rebull et al (2002), because their limiting magnitude is only I ∼ 17.9. It is clear that the vast majority of our faint sample have colours consistent with the NextGen isochrones for NGC 2264.…”

“…A brief examination of the reddening derived by previous authors is relevant at this point. At the galactic coordinates for NGC 2264 given by Rebull et al (2002), (l = 202.96, b = +2.22) the maps of Schlegel et al (1998) yield A v = 5.63, but it is considered that a background dark molecular cloud exists (Rebull et al 2002), limiting contamination by background giants. Indeed, these authors find a typical extinction towards NGC 2264 members A v ∼ 0.45 (from photometry and spectroscopy of latetype members), in good agreement with earlier values derived using small numbers of OB stars (Sung et al 1997;Park et al 2000).…”