Astron. Astrophys. 359, 82-102 (2000)

Kinematics of young stars ^*

I. Local irregularities

J. Torra, D. Fernández and F. Figueras

Departament d'Astronomia i Meteorologia, Universitat de Barcelona, Av. Diagonal 647, 08028 Barcelona, Spain

Received 29 July 1999 / Accepted 10 May 2000

Abstract

The local velocity field of young stars is dominated by the galactic rotation, the kinematics of the Gould Belt and the nearest OB associations and open clusters, and the kinematics of the spiral structure. We re-examined here this local velocity field by using a large sample of nearby O and B stars from the Hipparcos Catalogue. The high quality astrometric data are complemented with a careful compilation of radial velocities and Strömgren photometry, which allows individual photometric distances and ages to be derived. The Gould Belt extends up to 600 pc from the Sun with an inclination with respect to the galactic plane of - and the ascending node placed at -. Approximately 60% of the stars younger than 60 Myr belong to this structure. The values found for the Oort constants when different samples selected by age or distance were used allowed us to interpret the systematic trends observed as signatures induced by the kinematic behaviour of the Gould Belt. The contribution of Sco-Cen and Ori OB1 complexes in the characterization of the expansion of the Gould Belt system is also discussed. We found that a positive K-term remains when these aggregates are excluded. From the kinematic behaviour of the stars and their spatial distribution we derive an age for the Gould Belt system in the interval 30-60 Myr.

Key words: Galaxy: kinematics and dynamics Galaxy: solar neighbourhood Galaxy: structure stars: early-type stars: kinematics

* Based on data from the Hipparcos astrometry satellite (European Space Agency)

Send offprint requests to: J. Torra (jordi@am.ub.es)

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Contents

• 1. Introduction
• 2. The working sample
  • 2.1. Stellar distances
  • 2.2. Stellar radial velocities
  • 2.3. Stellar ages
  • 2.4. Working samples
• 3. The Gould Belt
  • 3.1. Structural parameters of the Gould Belt
  • 3.2. The age of the Gould Belt
• 4. Kinematics of young stars in the solar neighbourhood
  • 4.1. Fit of the kinematic model
    • 4.1.1. Equations for the linear model
    • 4.1.2. Resolution procedure
    • 4.1.3. Cosmic dispersion
  • 4.2. Large scale outline of the local galactic kinematics
  • 4.3. Local irregularities: the kinematic effects of the Gould Belt
• 5. Conclusions
• Acknowledgements
• Appendices
  • A: simulations to check the structure analysis
  • B: simulations to check the kinematic analysis
    • B.1. Process to generate the simulated samples
    • B.2. Results and discussion
• References

© European Southern Observatory (ESO) 2000

Online publication: June 30, 2000
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