Peculiarities of Open Star Clusters with High Vertical Velocities from the Region of the Sco-Cen OB Association

Abstract

We have studied the kinematics of a unique sample of young open star clusters (OSCs) with high vertical velocities, $15<W<40$ km s$^{-1}$. The characteristics of these clusters were taken from the catalogue by Hunt and Reffert (2023), where their mean proper motions, line-of-sight velocities, and distances were calculated using Gaia DR3 data. These OSCs are located within 0.6 kpc of the Sun and form two clumps: one in the region of the Sco-Cen OB association and the other one in the region of the Per OB3-Per OB2 associations. The OSC group of 47 members in the region of the Sco-Cen association is shown to expand along the $y$ axis, $\partial V/\partial y=51\pm12$ km s$^{-1}$ kpc$^{-1}$. This group also has a positive rotation around the $z$ axis with an angular velocity of $71\pm11$ km s$^{-1}$ kpc$^{-1}$ and a negative rotation around the $x$ axis with an angular velocity of $-35\pm5$ km s$^{-1}$ kpc$^{-1}$. Based on the velocities of 27 OSCs from the region of the Per OB3-Per OB2 associations, we have found no gradients differing significantly from zero. We have studied the kinematics of more than 1700 stars selected by Luhman (2022) as probable members of the Sco-Cen OB association. These stars are shown to have no high vertical velocities. The expansion coefficient of the stellar system in the $xy$ plane has been found from all stars to be $K_{xy}=43.2\pm2.2$ km s$^{-1}$ kpc$^{-1}$. Based on stars from the three UCL, LCC, and V1062 Sco groups with a mean age $\sim$20 Myr, for the first time we have found a volume expansion coefficient of the stellar system differing significantly from zero, $K_{xyz}=43.2\pm3.4$ km s$^{-1}$ kpc$^{-1}$.