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arXiv · 1705.09496

A Tale of Three Cities: OmegaCAM discovers multiple sequences in the color-magnitude diagram of the Orion Nebula Cluster

G. Beccari·M. G. Petr-Gotzens·H. M. J. Boffin·M. Romaniello·D. Fedele·G. Carraro·G. De Marchi·W. -J. de Wit·J. E. Drew·V. M. Kalari·C. F. Manara·E. L. Martin·S. Mieske·N. Panagia·L. Testi·J. S. Vink·J. R. Walsh·N. J. Wright
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Abstract

As part of the Accretion Discs in H$\alpha$ with OmegaCAM (ADHOC) survey, we imaged in r, i and H-alpha a region of 12x8 square degrees around the Orion Nebula Cluster. 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 for a revised look at the formation mode and early evolution of stars in clusters.

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G. Beccari, M. G. Petr-Gotzens, H. M. J. Boffin, M. Romaniello, D. Fedele, G. Carraro, G. De Marchi, W. -J. de Wit, J. E. Drew, V. M. Kalari, C. F. Manara, E. L. Martin, S. Mieske, N. Panagia, L. Testi, J. S. Vink, J. R. Walsh, N. J. Wright. 2017-05-26. A Tale of Three Cities: OmegaCAM discovers multiple sequences in the color-magnitude diagram of the Orion Nebula Cluster. https://doi.org/10.1051/0004-6361%2F201730432

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