Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21715217j&link_type=abstract
American Astronomical Society, AAS Meeting #217, #152.17; Bulletin of the American Astronomical Society, Vol. 43, 2011
Astronomy and Astrophysics
Astronomy
Scientific paper
Binaries are thought to be the primary heating energy source in globular clusters, since they can convert their binding energy to kinetic energy of the encounter stars through dynamical interactions. Even a small fraction of binaries are sufficient to prevent globular clusters from core collapse for many relaxation times. But the observed global binary fractions in globular clusters are still uncertain. Here we present our preliminary results for the binary fractions of 35 Galactic globular clusters with the HST archival data in the F606W and F814W bands. We use the secondary sequence method on the color-magnitude diagram to statistically account for the main-sequence-main-sequence binaries (primordial binaries). The binary fraction is obtained by fitting the residual color distribution after subtracting the color of the main-sequence ridge line, with properly modeling the photometric errors, field stars, and blending stars. We estimate the binary fractions with 3 different assumed binary mass-ratio distribution functions, and the current data sets are still not good to constrain the binary mass-ratio distributions. In our sample, we obtain a mean binary fraction of (9.1±4.1)% within their half-mass radii assuming a flat binary mass-ratio distribution. There is no clear trend for the binary fractions against the dynamical ages and [Fe/H], but binary fractions tend to increase with the absolute magnitudes of clusters. This is probably because less massive globular clusters consume fewer binaries through dynamical interactions due to their lower stellar density.
Bregman Joel N.
Ji Jun
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