Kavli Affiliate: Rainer Spurzem
| First 5 Authors: Qi Shu, Xiaoying Pang, Francesco Flammini Dotti, M. B. N. Kouwenhoven, Manuel Arca Sedda
| Summary:
We present a comprehensive investigation of main-sequence (MS) binaries in
the DRAGON simulations, which are the first one-million particles direct
$N$-body simulations of globular clusters. We analyse the orbital parameters of
the binary samples in two of the DRAGON simulations, D1-R7- IMF93 and
D2-R7-IMF01, focusing on their secular evolution and correlations up to 12 Gyr.
These two models have different initial stellar mass functions: Kroupa 1993
(D1-R7-IMF93) and Kroupa 2001 (D2-R7-IMF01); and different initial mass ratio
distributions: random paring (D1-R7-IMF93) and a power-law (D1-R7-IMF93). In
general, the mass ratio of a population of binaries increases over time due to
stellar evolution, which is less significant in D2-R7-IMF01. In D1-R7-IMF93,
primordial binaries with mass ratio $q approx$ 0.2 are most common, and the
frequency linearly declines with increasing $q$ at all times. Dynamical
binaries of both models have higher eccentricities and larger semi-major axes
than primordial binaries. They are preferentially located in the inner part of
the star cluster. Secular evolution of binary orbital parameters does not
depend on the initial mass-ratio distribution, but is sensitive to the initial
binary distribution of the system. At t = 12 Gyr, the binary fraction decreases
radially outwards, and mass segregation is present. A color difference of 0.1
mag in $F330W-F814W$ and 0.2 mag in $NUV-y$ between the core and the outskirts
of both clusters is seen, which is a reflection of the binary radial
distribution and the mass segregation in the cluster. The complete set of data
for primordial and dynamical binary systems at all snapshot intervals is made
publicly available.
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