A tale of three cities OmegaCAM discovers multiple sequences in the color-magnitude diagram of the Orion Nebula Cluster

作者：Beccari G^*; Petr Gotzens M G; Boffin H M J; Romaniello M; Fedele D; Carraro G; De Marchi G; de Wit W J; Drew J E; Kalari V M; Manara C F; Martin E L; Mieske S; Panagia N; Testi L; Vink J S; Walsh J R; Wright N J

来源：Astronomy & Astrophysics, 2017, 604: A22.

DOI：10.1051/0004-6361/201730432

• stars: pre-main sequence
• open clusters and associations: individual: Orion

As part of the accretion discs in H alpha with OmegaCAM (ADHOC) survey, we imaged a region of 12x8 square degrees around the Orion Nebula Cluster in r, i and H alpha. Thanks to the high-quality photometry obtained, we discovered three well-separated pre-main sequences in the color-magnitude diagram. The populations are all concentrated towards the cluster's center. Although several explanations can be invoked to explain these sequences, we are left with two competitive but intriguing scenarios: a population of unresolved binaries with an exotic mass ratio distribution, or three populations with different ages. Independent high-resolution spectroscopy supports the presence of discrete episodes of star formation, each separated by about a million years. The stars from the two putative youngest populations rotate faster than the older ones, in agreement with the evolution of stellar rotation observed in pre-main sequence stars younger than 4 Myr in several star forming regions. Whatever the final explanation, our results prompt a revised look at the formation mode and early evolution of stars in clusters.

• 出版日期2017-8