The Blue Straggler Population in the Globular Cluster M53 (NGC 5024): A Combined HST , LBT, and CFHT Study1 (original) (raw)

We used a proper combination of multiband high-resolution and wide field multi-wavelength observations collected at three different telescopes (HST, LBT and CFHT) to probe Blue Straggler Star (BSS) populations in the globular cluster M53. Almost 200 BSS have been identified over the entire cluster extension. The radial distribution of these stars has been found to be bimodal (similarly to that of several other clusters) with a prominent dip at ∼ 60 ′′ (∼ 2r c ) from the cluster center. This value turns out to be a factor of two smaller than the radius of avoidance (r avoid , the radius within which all the stars of ∼ 1.2 M ⊙ have sunk to the core because of dynamical friction effects in an Hubble time). While in most of the clusters with a bimodal BSS radial distribution, r avoid has been found to be located in the region of the observed minimum, this is the second case (after NGC6388) where this discrepancy is noted. This evidence suggests that in a few clusters the dynamical friction seems to be somehow less efficient than expected.