Astron. Astrophys. 333, 531-539 (1998)

New space motion of Galactic globular cluster Palomar 5

R.-D. Scholz ¹, M. Irwin ², M. Odenkirchen ³ and H. Meusinger <sup>4

1</sup> Astrophysikalisches Institut Potsdam, Sternwarte Babelsberg, An der Sternwarte 16, D-14482 Potsdam, Germany
² Royal Greenwich Observatory, Madingley Road, Cambridge CB3 OEZ, UK
³ Observatoire de Bordeaux, CNRS/INSU, BP 89, F-33270 Floirac, France
⁴ Thüringer Landessternwarte Tautenburg, D-07778 Tautenburg, Germany

Received 30 October 1997 / Accepted 9 February 1998

Abstract

A new space motion of the Galactic globular cluster Pal 5 has been obtained on the basis of the proper motion determination from 11 Schmidt plates with a time baseline of 39 years. A field of 1 square degree with nearly 400 galaxies defining the absolute reference frame has been used in the differential astrometry from plate-to-plate solutions. Residual systematic errors after the solutions with plate constant polynomials have been investigated and removed. Typical proper motion errors of 2 to 3 mas/yr were obtained for individual stars with magnitudes . Although our result for the mean absolute proper motion of Pal 5  mas/yr looks similar to the result of Schweitzer, Cudworth & Majewski (1993) based on different observations and reduction technique, the direction of the space motion we derive is completely different from theirs. Although the position of Pal 5 is near the orbital plane suggested for the Sagittarius dwarf galaxy by Ibata et al. (1997), both proper motion results suggest a total space velocity of Pal 5 significantly different from that to be expected from a tidally stripped fragment of the Sgr dwarf galaxy. In addition, our direction of motion of Pal 5 is almost in the opposite sense to that of the Sgr galaxy. Our Galactic orbit determination of Pal 5 and the star counts on the deep Schmidt plates indicate a smaller tidal radius of this globular cluster compared to previously published data of Webbink (1985) and Trager, King & Djorgovski (1995).

Key words: globular clusters: individual: Pal 5 methods: statistical astrometry stars: kinematics Galaxy: kinematics and dynamics

Send offprint requests to: R.-D. Scholz

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Contents

• 1. Introduction
• 2. Observations and measurements
• 3. Determination of absolute proper motions
  • 3.1. Systematic error removal
  • 3.2. Selection of reference galaxies
  • 3.3. Internal accuracy of proper motions
• 4. Mean absolute proper motion of the cluster
• 5. Space motion and Galactic orbit of Pal 5
• 6. Discussion of the results
• Acknowledgements
• References

© European Southern Observatory (ESO) 1998

Online publication: April 20, 1998
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