The dynamical distance and intrinsic structure of the globular cluster omega Centauri
| Autor: | E. K. Verolme, P. T. de Zeeuw, R. C. E. van den Bosch, G. van de Ven |
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| Rok vydání: | 2005 |
| Předmět: |
Physics
010308 nuclear & particles physics Astrophysics (astro-ph) FOS: Physical sciences Astronomy and Astrophysics Radius Astrophysics Astrophysics::Cosmology and Extragalactic Astrophysics Rotation 01 natural sciences Omega Distance modulus Space and Planetary Science Globular cluster 0103 physical sciences Orbit (dynamics) Omega Centauri Astrophysics::Earth and Planetary Astrophysics 010303 astronomy & astrophysics Schwarzschild radius Astrophysics::Galaxy Astrophysics |
| DOI: | 10.48550/arxiv.astro-ph/0509228 |
| Popis: | We determine the dynamical distance D, inclination i, mass-to-light ratio M/L and the intrinsic orbital structure of the globular cluster omega Cen, by fitting axisymmetric dynamical models to the ground-based proper motions of van Leeuwen et al. and line-of-sight velocities from four independent data-sets. We correct the observed velocities for perspective rotation caused by the space motion of the cluster, and show that the residual solid-body rotation component in the proper motions can be taken out without any modelling other than assuming axisymmetry. This also provides a tight constraint on D tan i. Application of our axisymmetric implementation of Schwarzschild's orbit superposition method to omega Cen reveals no dynamical evidence for a significant radial dependence of M/L. The best-fit dynamical model has a stellar V-band mass-to-light ratio M/L_V = 2.5 +/- 0.1 M_sun/L_sun and an inclination i = 50 +/- 4 degrees, which corresponds to an average intrinsic axial ratio of 0.78 +/- 0.03. The best-fit dynamical distance D = 4.8 +/- 0.3 kpc (distance modulus 13.75 +/- 0.13 mag) is significantly larger than obtained by means of simple spherical or constant-anisotropy axisymmetric dynamical models, and is consistent with the canonical value 5.0 +/- 0.2 kpc obtained by photometric methods. The total mass of the cluster is (2.5 +/- 0.3) x 10^6 M_sun. The best-fit model is close to isotropic inside a radius of about 10 arcmin and becomes increasingly tangentially anisotropic in the outer region, which displays significant mean rotation. This phase-space structure may well be caused by the effects of the tidal field of the Milky Way. The cluster contains a separate disk-like component in the radial range between 1 and 3 arcmin, contributing about 4% to the total mass. Comment: 37 pages (23 figures), accepted for publication in A&A, abstract abridged, for PS and PDF file with full resolution figures, see http://www.strw.leidenuniv.nl/~vdven/oc/ |
| Databáze: | OpenAIRE |
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