University of Hertfordshire

From the same journal

From the same journal


  • 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
  • Carlo Felice Manara
  • Eduardo L. Martin
  • S. Mieske
  • N. Panagia
  • L. Testi
  • Jorick S. Vink
  • J. R. Walsh
  • N. J. Wright
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Original languageEnglish
Article numberA22
Number of pages8
JournalAstronomy & Astrophysics
Early online date27 Jul 2017
Publication statusE-pub ahead of print - 27 Jul 2017


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.


Reproduced with permission from Astronomy & Astrophysics, © 2017 ESO. Published by EDP Sciences.

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