A nonparametric approach to the membership problem in open clusters.
Abstract
The problems derived from the use of the VasilevskisSanders method for obtaining membership probabilities in the vicinity of an open cluster are discussed. Some of the difficulties outlined can be bypassed employing a nonparametric model for the distributionsof the cluster and field stars. This allows for the posing of less restrictive astronomical hypothesis than assumed in the Vasilevskis model. In this manner, no assumption has been made either on the physical nature of the involved variables or on their statistical properties but the heterocedasticity of the populations. This allows the use of different sets of variables, such as multicolor photometry, radial velocities, and proper motions, to accomplish the same goal. Proper motions and positions are the variables selected in this study. The spatial data are introduced in order to enlarge the statistical distance between both populations. As an example of the application of this method the probable physical members of the cluster NGC 2420 have been determined. A sample of 282 stars observed by Cannon and Lloyd (1970) forms the input data. In this way a very clean colormagnitude diagram for this cluster has been obtained.
 Publication:

Astronomy and Astrophysics
 Pub Date:
 August 1990
 Bibcode:
 1990A&A...235...94C
 Keywords:

 Computational Astrophysics;
 Galactic Structure;
 Open Clusters;
 Astronomical Photometry;
 ColorMagnitude Diagram;
 Kinematics;
 Nonparametric Statistics;
 Probability Density Functions;
 Radial Velocity;
 Stellar Motions;
 Astrophysics