Structural parameters of 389 local open clusters

We fitted a King's function on the radial density profile of these clusters and a Gaussian Mixture Model (GMM) on their two dimensional distribution of members to study their shape. We also evaluated the degree of mass segregation of the clusters and the correlations of these parameters with the age and Galactic position of the clusters. Our methodology performs well on 389 clusters out of the 467 selected ones, including several recently discovered clusters that were poorly studied until now.

We report the detection of vast coronae around almost all the clusters and report the detection of 71 OCs with tidal tails, multiplying by more than four the number of such structures identified. We find the size of the cores to be on average smaller for old clusters than for young ones. Also, the overall size of the clusters seems to slightly increase with age while the fraction of stars in the halo seems to decrease.

As expected the mass segregation is more pronounced in the oldest clusters but a clear trend with age is not seen. OCs are more extended than previously expected, regardless of their age. The decrease in the proportion of stars populating the clusters halos highlights the different cluster evaporation processes and the short timescales they need to affect the clusters.

Reported parameters like cluster sizes or mass segregation levels all depend on cluster ages but can not be described as single functions of time.