Jordi, K. and Grebel, E. K. and Hilker, M. and Baumgardt, H. and Frank, M. and Kroupa, P. and Haghi, H. and Côté, P. and Djorgovski, S. G. (2009) Testing Fundamental Physics with Distant Star Clusters: Analysis of Observational Data on Palomar 14. Astronomical Journal, 137 (6). pp. 4586-4596. ISSN 0004-6256 http://resolver.caltech.edu/CaltechAUTHORS:20090828-094129210
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We use the distant outer halo globular cluster Palomar 14 as a test case for classical versus modified Newtonian dynamics (MOND). Previous theoretical calculations have shown that the line-of-sight velocity dispersion predicted by these theories can differ by up to a factor of 3 for such sparse, remote clusters like Pal 14. We determine the line-of-sight velocity dispersion of Palomar 14 by measuring radial velocities of 17 red giant cluster members obtained using the Very Large Telescope and Keck telescope. The systemic velocity of Palomar 14 is (72.28 ± 0.12) km s^(–1). The derived velocity dispersion of (0.38 ± 0.12) km s^(–1) of the 16 definite member stars is in agreement with the theoretical prediction for the classical Newtonian case according to Baumgardt et al. In order to exclude the possibility that a peculiar mass function might have influenced our measurements, we derived the cluster's main-sequence mass function down to 0.53 M⊙ using archival images obtained with the Hubble Space Telescope. We found a mass function slope of α = 1.27 ± 0.44, which is, compared to the canonical mass function, a significantly shallower slope. The derived lower limit on the cluster's mass is higher than the theoretically predicted mass in the case of MOND. Our data are consistent with a central density of ρ_0 = 0.1 M⊙ pc^(–3). We need no dark matter in Palomar 14. If the cluster is on a circular orbit, our spectroscopic and photometric results argue against MOND, unless the cluster experienced significant mass loss.
|Additional Information:||© 2009 The American Astronomical Society. Received 2008 December 23; accepted 2009 March 19; published 2009 April 15. We thank an anonymous referee for useful comments. We thank Marina Rejkuba for her advice deriving the radial velocities, and Katharina Glatt for her help with the isochrone fitting and the age determination of Pal 14. K.J. and E.K.G. acknowledge support from the Swiss National Foundation through grant numbers 20020-122140 and 20020-113697. S.G.D. acknowledges a partial support from the NSF grant AST-0407448.|
|Subject Keywords:||globular clusters: individual (Pal 14); gravitation; stellar dynamics|
|Official Citation:||Testing Fundamental Physics with Distant Star Clusters: Analysis of Observational Data on Palomar 14 K. Jordi, E. K. Grebel, M. Hilker, H. Baumgardt, M. Frank, P. Kroupa, H. Haghi, P. Côté, and S. G. Djorgovski 2009 The Astronomical Journal 137 4586-4596 doi: 10.1088/0004-6256/137/6/4586.|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||08 Sep 2009 21:50|
|Last Modified:||26 Dec 2012 11:16|
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