Refining the Dynamical Clock for Star Clusters
Abstract
We used a sample of 25 Galactic globular clusters to empirically measure the parameter A + recently introduced by Alessandrini et al., and defined as the area enclosed between the cumulative radial distribution of blue straggler stars (BSSs) and that of a reference population. Based on N-body simulations, this parameter is expected to efficiently measure the level of BSS central segregation. Observationally, for a proper cluster-to-cluster comparison we use {A}{rh}+, I.e., the value of the parameter determined out to the half-mass radius in each system. We find that {A}{rh}+ nicely correlates with the position of the minimum of the BSS normalized radial distribution and with the cluster central relaxation time. This demonstrates that it is a sensitive indicator of the cluster dynamical age as traced by the spatial segregation of the BSS population. In the context of the “stellar system dynamical clock,” this parameter provides a new clock-hand, which is easier to determine observationally and allows a more robust measure of the cluster dynamical age.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- December 2016
- DOI:
- 10.3847/2041-8213/833/2/L29
- Bibcode:
- 2016ApJ...833L..29L
- Keywords:
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- globular clusters: general;
- methods: observational;
- stars: kinematics and dynamics