Monoceros OB4: a new association in Gaia DR2

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 initial mass function, putting it on par in size with NGC2264. 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 x 60 pc.

Automated summary

Analysis of Gaia DR2 data revealed a new young star association, Monoceros OB4, co-moving with the Monoceros OB1 cloud complex. This association contains an estimated 1400-2500 stars and is expanding, indicating a larger and more complex Monoceros star formation region with an elongated arrangement of at least 300 x 60 pc.