Bibcode
DOI
Dalessandro, E.; Lanzoni, B.; Ferraro, F. R.; Rood, R. T.; Milone, A.; Piotto, G.; Valenti, E.
Bibliographical reference
The Astrophysical Journal, Volume 677, Issue 2, pp. 1069-1079.
Advertised on:
4
2008
Journal
Citations
81
Refereed citations
63
Description
We have used multiband high-resolution HST WFPC2 and ACS observations
combined with wide-field ground-based observations to study the blue
straggler star (BSS) population in the Galactic globular cluster NGC
6388. As in several other clusters we have studied, the BSS distribution
is found to be bimodal: highly peaked in the cluster center, rapidly
decreasing at intermediate radii, and rising again at larger radii. In
other clusters the sparsely populated intermediate-radius region (or
``zone of avoidance'') corresponds well to that part of the cluster
where dynamical friction would have caused the more massive BSSs or
their binary progenitors to settle to the cluster center. Instead, in
NGC 6388, BSSs still populate a region that should have been cleaned out
by dynamical friction effects, thus suggesting that dynamical friction
is somehow less efficient than expected. As a by-product of these
observations, the peculiar morphology of the horizontal branch (HB) is
also confirmed. In particular, within the (very extended) blue portion
of the HB we are able to clearly characterize three subpopulations:
ordinary blue HB stars, extreme HB stars, and blue hook stars. Each of
these populations has a radial distribution which is indistinguishable
from normal cluster stars.
Based on observations with the NASA/ESA Hubble Space Telescope, obtained
at the Space Telescope Science Institute, which is operated by AURA,
Inc., under NASA contract NAS5-26555. Also based on Wide Field Imager
observations collected at the European Southern Observatory, La Silla,
Chile.