Upper Scorpius and Ophiuchus members

We used a Gaussian Mixture Model to identify different kinematic structures in the 6D space of positions and velocities. We applied an orbital traceback analysis to estimate a dynamical traceback age for each group and determine the place where it was born. We identified seven different groups in this region.

Four groups (nu Sco, beta Sco, sigma Sco and delta Sco) are part of Upper Scorpius, two groups (rho Oph and alpha Sco) are in Ophiuchus, and another group (pi Sco) is a nearby young population. We found an age gradient from the rho Oph group (the youngest) to the delta Sco group (<~5Myr), showing that star formation was a sequential process for the past 5Myr. Our traceback analysis shows that Upper Scorpius and rho Oph groups share a common origin.

The closer group of pi Sco is probably older, and the traceback analysis suggests that this group and the alpha Sco group have a different origin, likely related to other associations in the Sco-Cen complex. Our study shows that this region has a complex star formation history that goes beyond the current formation scenario, likely a result of stellar feedback from massive stars, supernovae explosions, and dynamic interactions between stellar groups and the molecular gas.

In particular, we speculate that photo-ionisation from the massive delta Sco star could have triggered star formation first in the beta Sco group and then in the nu Sco group. The perturbations of stellar orbits due to stellar feedback and dynamical interactions could also be responsible for the 1-3Myr difference that we found between dynamical traceback ages and isochronal ages.