The Gaia-ESO Survey and CSI 2264: Substructures, disks, and sequential star formation in the young open cluster NGC 2264

Abstract

Context. Reconstructing the structure and history of young clusters is pivotal to understanding the mechanisms and timescales of early stellar evolution and planet formation. Recent studies suggest that star clusters often exhibit a hierarchical structure, possibly resulting from several star formation episodes occurring sequentially rather than a monolithic cloud collapse. Aims. We aim to explore the structure of the open cluster and star-forming region NGC 2264 ("3 Myr), which is one of the youngest, richest and most accessible star clusters in the local spiral arm of our Galaxy; we link the spatial distribution of cluster members to other stellar properties such as age and evolutionary stage to probe the star formation history within the region. Methods. We combined spectroscopic data obtained as part of the Gaia-ESO Survey (GES) with multi-wavelength photometric data from the Coordinated Synoptic Investigation of NGC 2264 (CSI 2264) campaign. We examined a sample of 655 cluster members, with masses between 0.2 and 1.8 M d and including both disk-bearing and disk-free young stars. We used T eff estimates from GES and g, r, i photometry from CSI 2264 to derive individual extinction and stellar parameters. Results. We find a significant age spread of 4-5 Myr among cluster members. Disk-bearing objects are statistically associated with younger isochronal ages than disk-free sources. The cluster has a hierarchical structure, with two main blocks along its latitudinal extension. The northern half develops around the O-type binary star S Mon; the southern half, close to the tip of the Cone Nebula, contains the most embedded regions of NGC 2264, populated mainly by objects with disks and ongoing accretion. The median ages of objects at different locations within the cluster, and the spatial distribution of disked and non-disked sources, suggest that star formation began in the north of the cluster, over 5 Myr ago, and was ignited in its southern region a few Myr later. Star formation is likely still ongoing in the most embedded regions of the cluster, while the outer regions host a widespread population of more evolved objects; these may be the result of an earlier star formation episode followed by outward migration on timescales of a few Myr. We find a detectable lag between the typical age of disk-bearing objects and that of accreting objects in the inner regions of NGC 2264: the first tend to be older than the second, but younger than disk-free sources at similar locations within the cluster. This supports earlier findings that the characteristic timescales of disk accretion are shorter than those of disk dispersal, and smaller than the average age of NGC 2264 (i.e., À3 Myr). At the same time, we note that disks in the north of the cluster tend to be shorter-lived ("2.5 Myr) than elsewhere; this may reflect the impact of massive stars within the region (notably S Mon), that trigger rapid disk dispersal. Conclusions. Our results, consistent with earlier studies on NGC 2264 and other young clusters, suppor...

The first spectroscopically confirmed brown dwarfs in NGC 2264

“…In Fig. 11 we compare the Teff derived by Lanzafame et al (2015) (used by Venuti et al (2018)) to the Teff calculated from the given spectral type. Lanzafame et al (2015) derive Teff by fitting a series of broadened and vieled template spectra to their target spectra.…”

“…In Fig. 10 we show the HR diagram, with absolute J-band magnitude plotted against effective temperature (Teff), for the 32 young sources identified in this study, as well as the Venuti et al (2018) sample of spectroscopically confirmed cluster members. Isochrones for 0.5, 3, 5 and 10 Myr are plotted in black, evolutionary tracks for 1 ⊙ , 0.5 ⊙ , 0.075 ⊙ and 0.02 ⊙ in grey (Baraffe et al 2015).…”

“…As one of the youngest and richest star forming regions accessible to deep surveys, NGC 2264 provides a perfect laboratory to study star and brown dwarf formation. Due to its large size of ∼ 1500 stellar members (Teixeira et al 2012;Rapson et al 2014;Venuti et al 2018), relative proximity of 719 ± 16 pc (Maíz Apellániz 2019) and low foreground extinction, NGC 2264 has been extensively studied for over 60 years (Herbig 1954) and will remain a principle region for star formation studies for the foreseeable future.…”

“…NGC 2264 is hierarchically structured with several subclusters of members. Separate populations in the cluster exhibit a range of ages (1-5 Myr), with evidence for sequential star formation starting in the north and spreading to the south (Sung & Bessell 2010;Venuti et al 2018;Nony et al 2020). The northern population surrounds the O-B-B triple system S Mon (Maíz Apellániz, J.…”

Decoding the Morphological Evolution of Open Clusters

“…Similarly, The structure in the right of the cluster is so, because of the positive direction and the value of the vector sum being about 199.71 ± 2.33 mas/yr. Furthermore, NGC 2264, a young star cluster, also has been widely studied by Venuti et al (2018); Orcajo et al (2019); Buckner et al (2020); Nony et al (2021). Figure 7 displays the vector diagrams of members of NGC 2264 in the twodimensional system.…”