Astron. Astrophys. 355, 537-551 (2000)

Distribution functions for evolved stars in the inner galactic plane

M.N. Sevenster ^1,3, H. Dejonghe ², K. Van Caelenberg ² and H.J. Habing <sup>1

1</sup> Sterrewacht Leiden, PO Box 9513, 2300 RA Leiden, The Netherlands
² Sterrenkundig Observatorium, Krijgslaan 281, 9000 Gent, Belgium
³ Presently at MSSSO/RSAA, Private Bag Weston Creek PO, Weston ACT 2611, Australia

Received 27 July 1999 / Accepted 3 January 2000

Abstract

We present dynamical distribution functions for a homogeneous sample of oxygen-rich, evolved, intermediate-mass stars in the inner galactic plane. We use an axisymmetric, two-component Stäckel potential that satisfies recent constraints on the galactic potential, amongst others a slightly declining local rotation curve. We show that this potential is adequate to model stellar-kinematic samples with radial extent ranging from 100 pc to 5 kpc in the Galaxy.

The stable two-integral model that gives the best fit to the first three projected moments provides a very good global representation of the data but fails to reproduce the central line-of-sight dispersion, the central apparent scaleheight and the almost-cylindrical rotation at intermediate longitudes (5^o 15^o). All these features, indicative of the galactic Bar, are fitted well by a three-integral model. We discuss various properties of the two- and three-integral distribution functions and the implications for galactic structure. A somewhat thicker disk component is needed to explain the observed distribution of older AGB stars in the plane; this component at the same time fits the kinematics of AGB stars at higher latitudes better than the thinner disk. We find that the Disk and the Bulge, as traced by AGB stars, are very similar dynamically and could well be one and the same component. There is a dynamically distinct component in the inner 100 pc of the Bulge, however.

Key words: Galaxy: kinematics and dynamics Galaxy: stellar content Galaxy: structure stars: AGB and post-AGB

Send offprint requests to: M. Sevenster (msevenst@mso.anu.edu.au)

This article contains no SIMBAD objects.

Contents

• 1. Introduction
• 2. Method
• 3. Implementation
  • 3.1. Data
  • 3.2. Potential
  • 3.3. Two-integral orbital components
• 4. Results
  • 4.1. Errors, biases and stability
• 5. Third integral
• 6. The central 100 pc
• 7. Discussion
  • 7.1. Density
  • 7.2. Orbits
  • 7.3. Dispersions
  • 7.4. Disk versus bulge
  • 7.5. Young versus old
• 8. Conclusions
• Acknowledgements
• Appendices
  • A: figures for derived models
• References

© European Southern Observatory (ESO) 2000

Online publication: March 9, 2000
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