Abstract
Context. Membership analyses of the DANCe and Tycho + DANCe data sets provide the largest and least contaminated sample of Pleiades candidate members to date. Aims. We aim at reassessing the different proposals for the number surface density of the Pleiades in the light of the new and most complete list of candidate members, and inferring the parameters of the most adequate model. Methods. We compute the Bayesian evidence and Bayes Factors for variations of the classical radial models. These include elliptical symmetry, and luminosity segregation. As a by-product of the model comparison, we obtain posterior distributions for each set of model parameters. Results. We find that the model comparison results depend on the spatial extent of the region used for the analysis. For a circle of 11.5 parsecs around the cluster centre (the most homogeneous and complete region), we find no compelling reason to abandon King’s model, although the Generalised King model introduced here has slightly better fitting properties. Furthermore, we find strong evidence against radially symmetric models when compared to the elliptic extensions. Finally, we find that including mass segregation in the form of luminosity segregation in the J band is strongly supported in all our models. Conclusions. We have put the question of the projected spatial distribution of the Pleiades cluster on a solid probabilistic framework, and inferred its properties using the most exhaustive and least contaminated list of Pleiades candidate members available to date. Our results suggest however that this sample may still lack about 20% of the expected number of cluster members. Therefore, this study should be revised when the completeness and homogeneity of the data can be extended beyond the 11.5 parsecs limit. Such a study will allow for more precise determination of the Pleiades spatial distribution, its tidal radius, ellipticity, number of objects and total mass.
Highlights
The projected spatial distribution (PSD), known as number surface density, of a stellar cluster is the two dimensional (2D) projection, in the plane of the sky, of its three dimensional (3D) space distribution
This explains why most of the previous works devoted to studying the spatial distribution of stars in clusters have been done using the PSD
In preparation for the analysis of these upcoming data sets and to narrow down the set of models that will be tested in the context of 3D studies, we have initiated a re-examination of the current analytical alternatives to describe the PSD of the Pleiades cluster
Summary
The projected spatial distribution (PSD), known as number surface density, of a stellar cluster is the two dimensional (2D) projection, in the plane of the sky, of its three dimensional (3D) space distribution. The same year, Raboud & Mermilliod (1998) fitted a King’s profile to a list of 270 candidate members with masses in the range 0.74–7.04 M , which were contained within a 5◦ radius area. They found a core radius of 1.5 pc and a tidal radius of 17.5 pc (7.5◦). Converse & Stahler (2008) fitted a King’s profile to a sample of 1245 candidate members from the Stauffer et al (2007) compilation These objects have masses greater than 0.08 M and are contained within a 5◦ radius.
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