Direct N-body simulations of globular clusters - I. Palomar 14

Zonoozi, Akram Hasani, Kupper, Andreas H. W., Baumgardt, Holger, Haghi, Hosein, Kroupa, Pavel and Hilker, Michael (2011) Direct N-body simulations of globular clusters - I. Palomar 14. Monthly Notices of Royal Astronomical Society, 411 3: 1989-2001. doi:10.1111/j.1365-2966.2010.17831.x

Author Zonoozi, Akram Hasani
Kupper, Andreas H. W.
Baumgardt, Holger
Haghi, Hosein
Kroupa, Pavel
Hilker, Michael
Title Direct N-body simulations of globular clusters - I. Palomar 14
Journal name Monthly Notices of Royal Astronomical Society   Check publisher's open access policy
ISSN 0035-8711
Publication date 2011-03
Year available 2010
Sub-type Article (original research)
DOI 10.1111/j.1365-2966.2010.17831.x
Open Access Status DOI
Volume 411
Issue 3
Start page 1989
End page 2001
Total pages 13
Place of publication Oxford, United Kingdom
Publisher Oxford University Press
Collection year 2011
Language eng
Abstract We present the first ever direct N-body computations of an old Milky Way globular cluster over its entire lifetime 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 10 times smaller than that in the solar neighbourhood. 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 cannot explain the mass function slope of Pal 14 when starting from the canonical Kroupa initial mass function (IMF). In order to seek 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 50 000 M⊙, 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 per cent 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 lifetime 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. © 2010 The Authors Monthly Notices of the Royal Astronomical Society © 2010 RAS
Keyword Methods: numerical
Globular clusters: individual: Palomar 14
Q-Index Code C1
Q-Index Status Confirmed Code
Institutional Status UQ
Additional Notes Article first published online: 6 Dec 2010

Document type: Journal Article
Sub-type: Article (original research)
Collections: School of Mathematics and Physics
Official 2011 Collection
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Created: Fri, 18 Feb 2011, 15:29:48 EST by Jo Hughes on behalf of Physics