Candidate Runaway Stars in the Cluster NGC 2180

The relative proper motions and tangential velocities of four stars from the cluster NGC 2180 are investigated using Gaia DR3 data. Our approach is to subtract the mean proper motion of the fields (the stars within a 1” radius around each target star) and the cluster from the motion of the target stars to calculate the relative proper motions with respect to their field and the cluster, respectively. From the relative proper motions of the target stars with respect to the field stars and the distance to the center of the cluster, we estimated the relative tangential velocities of our target stars. We use the astrometric excess noise information to filter the field stars from star-like objects, such as unresolved binaries. To eliminate foreground contaminations of the field stars used to figure out the relative proper motions of the target stars, we made a parallax cut, Color Magnitude Diagram (CMD) cut, and proper motion (PM) selection. The flight times of the target stars to the cluster NGC 2180 (kinematic ages) are calculated using angular separations from the cluster and their relative proper motions with respect to the cluster. All of the target stars have kinematic ages less than the age of the cluster. The stars, ID1 and ID3 have and with respect to their fields, which corresponds to the relative velocities respectively. These two stars could be runaways from the cluster because they have flight times from the cluster agreed with late ejection from the cluster and have larger proper. The remaining two stars, ID 2 and ID 4 have and with respect to the fields, which corresponds to the relative velocities and respectively, and could not be runaways as they have smaller proper motions, although their flight times to the cluster agreed with late ejection from the cluster.