Investigation of the Pleiades cluster. IV. The radial structure

TL;DR

This study analyzes the radial distribution, mass segregation, and structural parameters of the Pleiades cluster, revealing differences between single and binary stars and the cluster's elliptical outer shape.

Contribution

It provides detailed measurements of the Pleiades' radial structure, identifies new spectroscopic binaries, and discusses mass segregation and cluster shape based on member data.

Findings

Clear mass segregation between binaries and single stars

Elliptical shape of the outer cluster with ellipticity 0.17

Structural parameters like core and tidal radii are quantified

Abstract

On the basis of the best available member list and duplicity information, we have studied the radial distribution of 270 stars and multiple systems earlier than K0 in the Pleiades. Five new long period spectroscopic binaries have been identified from the CORAVEL observations. We have found a clear mass segregation between binaries and single stars, which is explained by the greater average mass of the multiple systems. The mass function of the single stars and primaries appears to be significantly different. While the central part of the cluster is spherical, the outer part is clearly elliptical, with an ellipticity of 0.17. The various parameters describing the Pleiades are (for a distance of 125 pc): core radius r_{c}=0.6 deg (1.4 pc), tidal radius r_{t}=7.4 deg (16 pc), half mass radius r_{m/2}=0.88 deg (1.9 pc), harmonic radius r=1.82 deg (4 pc). Low-mass stars (later than K0) probably extend further out and new proper motion and radial velocity surveys over a larger area and to fainter magnitudes would be very important to improve the description of the cluster structure and complete mass function.