The Distribution of Stellar Mass in the Pleiades

TL;DR

This study analyzes the stellar mass distribution in the Pleiades cluster, revealing a high binary fraction, correlated binary component masses, and clear mass segregation, using statistical and spatial analysis techniques.

Contribution

It introduces a maximum likelihood method for determining mass distributions and a new approach to quantify mass segregation in star clusters.

Findings

Binary fraction for unresolved pairs is 68%, rising to 76% when including resolved systems.

Primary and secondary star masses in binaries are correlated.

Clear evidence of mass segregation in the Pleiades.

Abstract

As part of an effort to understand the origin of open clusters, we present a statistical analysis of the currently observed Pleiades. Starting with a photometric catalog of the cluster, we employ a maximum likelihood technique to determine the mass distribution of its members, including single stars and both components of binary systems. We find that the overall binary fraction for unresolved pairs is 68%. Extrapolating to include resolved systems, this fraction climbs to about 76%, significantly higher than the accepted field-star result. Both figures are sensitive to the cluster age, for which we have used the currently favored value of 125 Myr. The primary and secondary masses within binaries are correlated, in the sense that their ratios are closer to unity than under the hypothesis of random pairing. We map out the spatial variation of the cluster's projected and three-dimensional mass and number densities. Finally, we revisit the issue of mass segregation in the Pleiades. We find unambiguous evidence of segregation, and introduce a new method for quantifying it.