The Blue Straggler Population in the Globular Cluster M53 (NGC 5024): A Combined HST, LBT, and CFHT Study
Pasian, F.; Fontana, A.; Grazian, A.; Giallongo, E.; Bellazzini, M.; Pulone, L.; Gentile, G.; Ragazzoni, R.; Testa, V.; Beccari, G.; Di Paola, A.; Baruffolo, A.; Ferraro, F. R.; Fusi Pecci, F.; Buschkamp, P.; Lanzoni, B.; Farinato, J.; Rood, R. T.; De Santis, C.; Gallozzi, S.; Speziali, R.; Diolaiti, E.; Smareglia, R.; Pedichini, F.; Gasparo, F.; Vernet, E.; Bouche, N.
Italy, United States, Germany
Abstract
We used a proper combination of high-resolution and wide-field multiwavelength observations collected at three different telescopes (HST, LBT, and CFHT) to probe the blue straggler star (BSS) population in the globular cluster M53. Almost 200 BSSs have been identified over the entire cluster extension. The radial distribution of these stars has been found to be bimodal (similar to that of several other clusters) with a prominent dip at ~60'' (~2rc) from the cluster center. This value turns out to be a factor of 2 smaller than the radius of avoidance (ravoid, the radius within which all the stars of ~1.2 M⊙ have sunk to the core because of dynamical friction effects in a Hubble time). While in most of the clusters with a bimodal BSS radial distribution, ravoid has been found to be located in the region of the observed minimum, this is the second case (after NGC 6388) where this discrepancy is noted. This evidence suggests that in a few clusters the dynamical friction seems to be somehow less efficient than expected. We have also used this database to construct the radial star density profile of the cluster; this is the most extended and accurate radial profile ever published for this cluster, including detailed star counts in the very inner region. The star density profile is reproduced by a standard King Model with an extended core (~25'') and a modest value of the concentration parameter (c = 1.58). A deviation from the model is noted in the most external region of the cluster (at r > 6.5' from the center). This feature needs to be further investigated in order to address the possible presence of a tidal tail in this cluster.
Based on observations with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada-France-Hawaii Telescope (CFHT), which is operated by the National Research Council (NRC) of Canada, the Institute National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii. Based on observations with the NASA/ESA HST, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS5-26555. Also based on data acquired using the Large Binocular Telescope (LBT). The LBT is an international collaboration among institutions in the United States, Italy, and Germany. LBT Corporation partners are The University of Arizona on behalf of the Arizona university system; Istituto Nazionale di Astrofisica, Italy; LBT Beteiligungsgesellschaft, Germany, representing the Max-Planck Society, the Astrophysical Institute Potsdam, and Heidelberg University; The Ohio State University; and The Research Corporation, on behalf of The University of Notre Dame, University of Minnesota and University of Virginia. This research used the facilities of the Canadian Astronomy Data Centre operated by the National Research Council of Canada with the support of the Canadian Space Agency.