Space Velocities of Southern Globular Clusters. V. A Low Galactic Latitude Sample

We have measured the absolute proper motions of globular clusters NGC 2808, 3201, 4372, 4833, 5927, and 5986. The proper motions are on the Hipparcos system, and they are the first determinations ever made for these low Galactic latitude clusters. The proper-motion uncertainties range from 0.3 to 0.5 mas yr-1. The inferred orbits indicate that (1) the single metal-rich cluster in our sample, NGC 5927, dynamically belongs to the thick disk; (2) the remaining metal-poor clusters have rather low-energy orbits of high eccentricity, and among these there appear to be two pairs of dynamically associated clusters; (3) the most energetic cluster in our sample, NGC 3201, is on a highly retrograde orbit?which had already been surmised from radial velocity alone?with an apocentric distance of 22 kpc; and (4) none of the metal-poor clusters appear to be associated with the recently detected SDSS streams or with the Monoceros structure. These are the first results of the Southern Proper Motion program where the second-epoch observations are taken with the recent CCD camera system installed on the double astrograph at El Leoncito, Argentina.

[1]  H. C. Hamaker,et al.  Approximating the Cumulative Normal Distribution and its Inverse , 1978 .

[2]  R. Zinn.  The globular cluster system of the galaxy. IV - The halo and disk subsystems , 1985 .

[3]  T. Armandroff.  Color-magnitude diagrams for six metal-rich, low-latitude globular clusters , 1988 .

[4]  W. Grundy,et al.  Relative proper motions and the stellar velocity dispersion of the open cluster M67 , 1989 .

[5]  Brian McLean,et al.  The Guide Star Catalog. I. Astronomical Foundations and Image Processing , 1990 .

[6]  David N. Spergel,et al.  The Disruption of the Sagittarius Dwarf Galaxy. , 1995 .

[7]  Dynamics of the Galactic Globular Cluster NGC 3201 , 1995, astro-ph/9506042.

[8]  E. Bertin,et al.  SExtractor: Software for source extraction , 1996 .

[9]  William E. Harris,et al.  A Catalog of Parameters for Globular Clusters in the Milky Way , 1996 .

[10]  Discovery of Extended Blue Horizontal Branches in Two Metal-rich Globular Clusters* , 1997, astro-ph/9705039.

[11]  R. Mendez,et al.  Space velocities of southern globular clusters. I. Astrometric techniques and first results. , 1997 .

[12]  G. González,et al.  Elemental Abundances in Giants in NGC 3201, a Globular Cluster with a Retrograde Orbit , 1998 .

[13]  Vera Kozhurina-Platais,et al.  The Southern Proper Motion Program. II. A Catalog at the South Galactic Pole , 1998 .

[14]  V. Kozhurina-Platais,et al.  The Southern Proper Motion Program. I. Magnitude Equation Correction , 1998 .

[15]  W. V. Altena,et al.  Space Velocities of Southern Globular Clusters. II. New Results for 10 Clusters , 1999 .

[16]  Terrence M. Girard,et al.  Space Velocities of Globular Clusters. III. Cluster Orbits and Halo Substructure , 1999 .

[17]  Norbert Zacharias,et al.  The First US Naval Observatory CCD Astrograph Catalog , 2000 .

[18]  Amina Helmi,et al.  Mapping the substructure in the Galactic halo with the next generation of astrometric satellites , 2000, astro-ph/0007166.

[19]  Photometric catalog of nearby globular clusters. II. A large homogeneous (V,I) color-magnitude diagram data-base , 2000, astro-ph/0006299.

[20]  J. Melbourne,et al.  CCD Photometry of the Globular Cluster NGC 4833 and Extinction Near the Galactic Plane , 2000, astro-ph/0009401.

[21]  S. R. Majewski,et al.  The Absolute Proper Motion of Palomar 12: A Case for Tidal Capture from the Sagittarius Dwarf Spheroidal Galaxy , 2000, astro-ph/0006314.

[22]  H. Bond,et al.  CCD Photometry of the Globular Cluster NGC 5986 and Its Post-Asymptotic Giant Branch and RR Lyrae Stars , 2000, astro-ph/0010095.

[23]  Orbits of Globular Clusters in the Outer Galaxy: NGC 7006 , 2001, astro-ph/0106259.

[24]  Heather A. Rave,et al.  The Ghost of Sagittarius and Lumps in the Halo of the Milky Way , 2001, astro-ph/0111095.

[25]  Yale University,et al.  Remnants of the Sagittarius Dwarf Spheroidal Galaxy around the Young Globular Cluster Palomar 12 , 2002, astro-ph/0203296.

[26]  W. V. Altena,et al.  Space Velocities of Southern Globular Clusters. IV. First Results for Inner Galaxy Clusters , 2002, astro-ph/0212279.

[27]  A. Robin,et al.  A synthetic view on structure and evolution of the Milky Way , 2003 .

[28]  D. Dinescu,et al.  A Capture Scenario for the Globular Cluster ω Centauri , 2003, astro-ph/0304262.

[29]  Jeffrey D. Crane,et al.  Star Clusters in the Galactic Anticenter Stellar Structure and the Origin of Outer Old Open Clusters , 2004 .

[30]  D. Monet,et al.  The Southern Proper Motion Program. III. A Near-Complete Catalog to V = 17.5 , 2004, astro-ph/0402411.

[31]  Yale University,et al.  Disruption of a dwarf galaxy under strong shocking: the origin of ω Centauri , 2004 .

[32]  J. Norris.  The Helium Abundances of ω Centauri , 2004 .

[33]  A. Mackey,et al.  Comparing the properties of local globular cluster systems: implications for the formation of the Galactic halo , 2004, astro-ph/0408404.

[34]  S. Derriere,et al.  Erratum: A synthetic view on structure and evolution of the Milky Way , 2004 .

[35]  Judith Cohen,et al.  Palomar 12 as a Part of the Sagittarius Stream: The Evidence from Abundance Ratios , 2003, astro-ph/0311187.

[36]  B. Gibson,et al.  The Galactic Inner Halo: Searching for White Dwarfs and Measuring the Fundamental Galactic Constant, Θ0/R0 , 2003, astro-ph/0304036.

[37]  T. Girard,et al.  Absolute Proper Motion of the Sagittarius Dwarf Galaxy and of the Outer Regions of the Milky Way Bulge , 2004 .

[38]  M. Irwin,et al.  A Comparison of Elemental Abundance Ratios in Globular Clusters, Field Stars, and Dwarf Spheroidal Galaxies , 2005, astro-ph/0506238.

[39]  A Comprehensive Model for the Monoceros Tidal Stream , 2004, astro-ph/0410448.

[40]  Giampaolo Piotto,et al.  Metallicities on the Double Main Sequence of ω Centauri Imply Large Helium Enhancement , 2004, astro-ph/0412016.

[41]  A Helium Spread among the Main-Sequence Stars in NGC 2808 , 2005, astro-ph/0505347.

[42]  C. Ree,et al.  Super-Helium-rich Populations and the Origin of Extreme Horizontal-Branch Stars in Globular Clusters , 2005, astro-ph/0501500.

[43]  Observatoire de la Côte d'Azur,et al.  Na-O anticorrelation and HB. I. The Na-O anticorrelation in NGC 2808 , 2005, astro-ph/0511833.

[44]  DETECTION OF A 63 COLD STELLAR STREAM IN THE SLOAN DIGITAL SKY SURVEY , 2006, astro-ph/0604332.

[45]  The Origin of the Double Main Sequence in ω Centauri: Helium Enrichment due to Gas Fueling from Its Ancient Host Galaxy? , 2005, astro-ph/0512385.

[46]  F. D’Antona,et al.  NGC 6441: another indication of very high helium content in globular cluster stars , 2006, astro-ph/0610406.

[47]  J. Lattanzio,et al.  The Chemical Evolution of Helium in Globular Clusters: Implications for the Self-Pollution Scenario , 2006, astro-ph/0608366.

[48]  U. Zurich,et al.  The Orbits of 48 Globular Clusters in a Milky Way-like Barred Galaxy , 2006, astro-ph/0609357.

[49]  Abundances in Red Giant Stars of NGC 2808 and Correlations between Chemical Anomalies and Global Parameters in Globular Clusters , 2005, astro-ph/0511144.

[50]  Multivariate analysis of globular cluster horizontal branch morphology: searching for the second parameter , 2005, astro-ph/0511704.

[51]  K. Bekki.  Primordial pollution of globular clusters within their host dwarfs embedded in dark matter haloes at high redshifts , 2005, astro-ph/0512467.

[52]  B. Yanny,et al.  An Orphan in the "Field of Streams" , 2007 .

[53]  Santiago,et al.  The exotic chemical composition of the Sagittarius dwarf Spheroidal galaxy , 2006 .

[54]  The chemical evolution of Omega Centauri's progenitor system , 2007, astro-ph/0701162.

[55]  Michael Perryman,et al.  Astronomical Applications of Astrometry: The Hipparcos and Tycho Catalogues , 2008 .

[56]  Hiroyuki Mito,et al.  The IRSA 2MASS all-sky point source catalog , 2008 .