Astronomy and Astrophysics, volume 604A, 22-22 (2017/8-1)
A tale of three cities. OmegaCAM discovers multiple sequences in the color-magnitude diagram of the Orion Nebula Cluster.
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. and WRIGHT N.J.
Abstract (from CDS):
As part of the accretion discs in Hα with OmegaCAM (ADHOC) survey, we imaged a region of 12x8 square degrees around the Orion Nebula Cluster in r, i and Hα. 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 4Myr 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.
© ESO, 2017
stars: pre-main sequence - open clusters and associations: individual: Orion - open clusters and associations: individual: Orion
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