Monoceros OB4: a new association in Gaia DR2

TL;DR

Using Gaia DR2 data, the study identifies a new young stellar association, Monoceros OB4, revealing a larger, complex star formation region with an unbound, expanding population of 1400-2500 stars.

Contribution

The paper reports the discovery and characterization of Monoceros OB4, a new young stellar association in Gaia DR2 data, expanding understanding of the Monoceros star formation complex.

Findings

Monoceros OB4 contains 1400-2500 stars.

It is unbound and expanding.

The association is at least 300 x 60 pc in size.

Abstract

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 x 60 pc.