We present the first ever direct N -body computations of an old Milky Way globular cluster over its entire life time on a star-by-star basis .
Using recent GPU hardware at Bonn University , we have performed a comprehensive set of N -body calculations to model the distant outer halo globular cluster Palomar 14 ( Pal 14 ) .
Pal 14 is unusual in that its mean density is about ten times smaller than that in the solar neighborhood .
Its large radius as well as its low-mass make it possible to simulate Pal 14 on a star-by-star basis .
By varying the initial conditions we aim at finding an initial N -body model which reproduces the observational data best in terms of its basic parameters , i.e .
half-light radius , mass and velocity dispersion .
We furthermore focus on reproducing the stellar mass function slope of Pal 14 which was found to be significantly shallower than in most globular clusters .

While some of our models can reproduce Pal 14 ’ s basic parameters reasonably well , we find that dynamical mass segregation alone can not explain the mass function slope of Pal 14 when starting from the canonical Kroupa initial mass function ( IMF ) .
In order to seek for an explanation for this discrepancy , we compute additional initial models with varying degrees of primordial mass segregation as well as with a flattened IMF .
The necessary degree of primordial mass segregation turns out to be very high , though , such that we prefer the latter hypothesis which we discuss in detail .
This modelling has shown that the initial conditions of Pal 14 after gas expulsion must have been a half-mass radius of about 20 pc , a mass of about 50000 M _ { \odot } , and possibly some mass segregation or an already established non-canonical IMF depleted in low-mass stars .
Such conditions might be obtained by a violent early gas-expulsion phase from an embedded cluster born with mass segregation .
Only at large Galactocentric radii are clusters likely to survive as bound entities the destructive gas-expulsion process we seem to have uncovered for Pal 14 .

In addition we compute a model with a 5 % primordial binary fraction to test if such a population has an effect on the cluster ’ s evolution .
We see no significant effect , though , and moreover find that the binary fraction of Pal 14 stays almost the same and gives the final fraction over its entire life time due to the cluster ’ s extremely low density .
Low-density , halo globular clusters might therefore be good targets to test primordial binary fractions of globular clusters .