# The Formation Timescale of the Young Open Cluster NGC 2264: Implication on the Lithium Abundance Distribution of Pre-Main Sequence Stars

• Lim, Beomdu (Korea Astronomy & Space Science Institute) ;
• Sung, Hwankyung (Sejong University) ;
• Kim, Jinyoung S. (Steward Observatory) ;
• Bessell, Michael S. (RSAA, Australian National University) ;
• Hwang, Narae (Korea Astronomy & Space Science Institute) ;
• Park, Byeong-Gon (Korea Astronomy & Space Science Institute)
• Published : 2016.10.12

#### Abstract

The duration of star formation activity is a key to understanding the formation process of star clusters. Although a number of astronomers have attempted to derive the underlying age spread in photometric diagrams with a variety of stellar evolutionary models, the resultant findings are subject to uncertainties due to intrinsic variability of pre-main sequence (PMS) stars, observational errors, difficulties in reddening correction, and systematic differences in adopted stellar evolutionary models. The distribution of Li abundance for PMS stars in a cluster could, on the other hand, provide an alternative way to estimate the age spread. In this study, a total of 134 PMS stars in NGC 2264 are observed with the high resolution multi-object spectrogragh Hectochelle attached to the 6.5m Multi Mirror Telescope. We have successfully detected Li ${\lambda}6708$ resonance doublet for 86 low-mass PMS stars. The Li abundance of the stars is derived from their equivalent width using a curves of growth method. After correction for non-LTE effects, the underlying age spread of 3 - 4 Myr is inferred from the Li abundance distribution of low-mass PMS stars. We suggest that NGC 2264 formed on a timescale shorter than 5 Myr given the presence of embedded populations.