Astron. Astrophys. 337, 125-140 (1998)

The overlapping open clusters NGC 1750 and NGC 1758

III. Cluster-field segregation and clusters physical parameters

D. Galadi-Enríquez ¹, C. Jordi ¹ and E. Trullols <sup>1, 2

1</sup> Dept. d'Astronomia i Meteorologia, Univ. de Barcelona, Avda. Diagonal 647, E-08028 Barcelona, Spain
² Dept. de Matemàtica Aplicada i Telemàtica, Univ. Politècnica de Catalunya, Avda. Víctor Balaguer s/n, E-08800 Vilanova i la Geltrú, Spain

Received 2 March 1998 / Accepted 22 June 1998

Abstract

Cluster-field segregation and determination of physical parameters of the open clusters NGC 1750 and NGC 1758 were performed from CCD and photographic photometric and astrometric surveys previously published by the authors. Membership probabilities were computed to a brightness limit of mag through a non-standard method in a fully non-parametric approach, using proper motions, positions and photometry.

This study allowed several parameters for NGC 1750 and NGC 1758 to be determined, including position, size, density profile, absorption, distance, age, luminosity function and mass. The common colour excess of both clusters is  mag. NGC 1750 is slightly younger (), closer ( mag) and less concentrated than NGC 1758 ( and  mag). We also conclude that NGC 1746 is an erroneous assignation (not corresponding to any real open cluster), and that NGC 1750 and NGC 1758 are overlapping clusters, but they do not constitute a gravitationally bounded system.

Key words: open clusters and associations: individual: NGC 1746 open clusters and associations: individual: NGC 1750 open clusters and associations: individual: NGC 1758 stars: luminosity function, mass function methods: statistical

Send offprint requests to: D. Galadí-Enríquez
Correspondence to: dgaladi@pchpc5.am.ub.es

SIMBAD Objects

Contents

• 1. Introduction
• 2. Membership probabilities from empirical frequency functions
  • 2.1. Membership probabilities: general formulation
  • 2.2. Frequency functions: parametric models
  • 2.3. Drawbacks of the parametric approach
  • 2.4. Frequency functions: non-parametric method
• 3. Empirical frequency functions: application to our sample
  • 3.1. Kinematic plane: proper motions
  • 3.2. Spatial plane: x and y coordinates
  • 3.3. Photometric plane: photographic colour-magnitude diagram
• 4. Membership determination
  • 4.1. Selection criteria
  • 4.2. Bright stars
• 5. Physical parameters of the clusters
  • 5.1. Spatial parameters: positions, sizes and density profiles
  • 5.2. Absorption and colour excess
  • 5.3. Distance and age determinations
  • 5.4. Luminosity functions
• 6. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1998

Online publication: August 6, 1998
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