Kinematics of NGC 2264: Signs of Cluster Formation

Abstract

We present results from 1078 high resolution spectra of 990 stars in the young open cluster NGC 2264, obtained with the Hectochelle multiobject echelle spectrograph on the 6.5m MMT. We confirm 471 stars as members, based on their radial velocity and/or Hα emission. The radial velocity distribution of cluster members is non-Gaussian with a dispersion of σ ≈ 3.5km s −1 . We find a substantial north-south velocity gradient and spatially coherent structure in the radial velocity distribution, similar to that seen in the molecular gas in the region. Our results suggest that there are at least three distinguishable subclusters in NGC 2264, correlated with similar structure seen in 13 CO emission, which is likely to be a remnant of initial structure in this very young cluster. We propose that this substructure is the result of gravitational amplification of initial inhomogeneities during overall collapse to a filamentary distribution of gas and stars, as found in simulations by Burkert & Hartmann (2004).

A Constraint on the Formation Timescale of the Young Open Cluster NGC 2264: Lithium Abundance of Pre-Main Sequence Stars

“…explosion about 6-7 Myr ago was suspected as the source of the external trigger. The presence of the subclusters can also be found in the velocity field obtained from 13 CO observations and stellar radial velocity survey (Fűrész et al 2006;Tobin et al 2015). The radial velocity distribution of the cluster members shows a velocity gradient of 10 km s −1 along the north-south direction.…”

“…The star shows a weak Hα absorption line and broad metallic lines. Fűrész et al (2006) identified the star as a spectroscopic binary from their multi-epoch spectroscopic observations. The star is brighter than other stars at a given color in Figure 10.…”

“…Hence, the adopted error of 0.2 dex is likely the true uncertainty. According to Fűrész et al (2006) and Sung et al (2009), NGC 2264 is comprised of at least three subclusters-the S Mon, Spokes, and Cone nebula regions as shown in Figure 9. In addition, a low stellar density region (halo) surrounds these subclusters (Sung et al 2008).…”

Star formation in the Gaia era

“…To better understand this evolution we also need to study what is happening in the kinematic subspace during this evolution. There have already been a number of detections of kinematic substructure (e.g., Fűrész et al, 2006;Jeffries et al, 2014, see Figure 7), suggesting it might be a very common phenomenon in young star forming structures. Emilio explained how this kinematic substructure can be detected and measured using the minimum spanning tree, an algorithm that has already been effective in diagnosing spatial substructure (Cartwright & Whitworth, 2004).…”

“…(Hénault-Brunet et al, 2012) and kinematic substructure (Fűrész et al, 2006;Jeffries et al, 2014, see Figure 7). Proper motions and radial velocities can also be used to measure kinematic parallaxes, which Galli et al (2013) used to reveal significant depth effects between the different subgroups of the Lupus associations, showing that the (likely older) weak-lined T-Tauri stars are more dispersed in both angular extent and depth compared to the (younger) Classical T-Tauri stars.…”