A Tale of Three Cities : OmegaCAM discovers multiple sequences in the color-magnitude diagram of the Orion Nebula Cluster
View/
Author
Beccari, G.
Petr-Gotzens, M.G.
Boffin, H.M.J.
Romaniello, M.
Fedele, D.
Carraro, G.
Marchi, G. De
de Wit, W.J.
Drew, J. E.
Kalari, V. M.
Manara, Carlo Felice
Martin, Eduardo L.
Mieske, S.
Panagia, N.
Testi, L.
Vink, Jorick S.
Walsh, J. R.
Wright, N. J.
Attention
2299/20394
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.