Monoceros OB4: a new association in Gaia DR2

P S Teixeira, J Alves, A Sicilia-Aguilar, A Hacar, A Scholz

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We use Gaia DR2 data to survey the classic Monoceros OB1 region and look for the existence of a dispersed young population, co-moving with the cloud complex. An analysis of the distribution of proper motions reveals a 20-30 Myr association of young stars, about 300-400 pc away from the far side of the Mon OB1 complex, along the same general line-of-sight. We characterize the new association, Monoceros OB4, and estimate it contains between 1400 and 2500 stars, assuming a standard IMF, putting it on par in size with NGC 2264. We find from the internal proper motions that Mon OB4 is unbound and expanding. Our results seem to unveil a larger and more complex Monoceros star formation region, suggesting an elongated arrangement that seems to be at least 300 × 60 pc.
Original languageEnglish
Pages (from-to)L17–L21
Number of pages5
JournalMonthly Notices of the Royal Astronomical Society: Letters
Issue number1
Early online date31 Mar 2021
Publication statusPublished - Jun 2021


  • ISM: individual objects: Monoceros OB1 cloud complex
  • Stars: pre-main-sequence
  • Galaxy: open clusters and association: general


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