The Dynamical State and Blue Straggler Population of the Globular Cluster NGC 6266 (M62)

Abstract

We have used a proper combination of multiband high-resolution Hubble Space Telescope WFPC2 and wide-field ground-based observations to image the Galactic globular cluster NGC 6266 (M62). The extensive photometric data set allows us to determine the center of gravity and to construct the most extended radial profile ever published for this cluster including, for the first time, detailed star counts in the very inner region. The star density profile is well reproduced by a standard King model with an extended core (~19") and a modest value of the concentration parameter (c=1.5), indicating that the cluster has not yet experienced core collapse. The millisecond pulsar population (whose members are all in binary systems) and the X-ray-emitting population (more than 50 sources within the cluster half-mass radius) suggest that NGC 6266 is in a dynamical phase particularly active in generating binaries through dynamical encounters. UV observations of the central region have been used to probe the population of blue straggler stars, whose origin might be also affected by dynamical interactions. The comparison with other globular clusters observed with a similar strategy shows that the blue straggler content in NGC 6266 is relatively low, suggesting that the formation channel that produces binary systems hosting neutron stars or white dwarfs is not effective in significantly increasing the blue straggler population. Moreover, an anticorrelation between millisecond pulsar content and blue straggler specific frequency in globular clusters seems to be emerging with increasing evidence.

Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under NASA contract NAS5-26555. Also based on Wide Field Imager observations collected at the European Southern Observatory (ESO), La Silla, Chile, within the observing programs 62.L-0354 and 64.L-0439.