A search for mass segregation of stars and brown dwarfs in ρ Ophiuchi

Richard J. Parker,Thomas Maschberger,Catarina Alves de Oliveira

doi:10.1111/j.1365-2966.2012.21790.x

Abstract

We apply two different algorithms to search for mass segregation to a recent observational census of the rho Ophiuchi star forming region. Firstly, we apply the Lambda_MSR method, which compares the minimum spanning tree (MST) of a chosen subset of stars to MSTs of random subsets of stars in the cluster, and determine the mass segregation ratio, Lambda_MSR. Secondly, we apply the m-Sigma method, which calculates the local stellar surface density around each star and determines the statistical significance of the average surface density for a chosen mass bin, compared to the average surface density in the whole cluster. Using both methods, we find no indication of mass segregation (normal or inverse) in the spatial distribution of stars and brown dwarfs in rho Ophiuchi. Although rho Ophiuchi suffers from high visual extinction, we show that a significant mass segregation signature would be detectable, albeit slightly diluted, despite dust obscuration of centrally located massive stars.

Highlights

Most stars form in groups, clusters, and larger associations
4.1 ΛMSR for high mass stars In Fig. 2 we show the evolution of ΛMSR as a function of the number of stars in an minimum spanning tree (MST), NMST for the most massive stars in the cluster
We increase the number of stars in the MST in steps of 6, which is a compromise between a high enough resolution to pick out structure between different mass regimes, and a low enough resolution so that we do not add noise to the plot

Summary

Introduction

Most stars form in groups, clusters, and larger associations. In order to understand the star formation process, it is desirable to quantify the spatial distribution of stars in different star forming regions, so that a clear picture of the formation and evolution of each region can be drawn. Allison et al (2009a) found that the amount of mass segregation in the ONC could be quantified by comparing the minimum spanning trees (MSTs) of chosen subsets of stars to the MSTs of random sets of stars. If the MST of the most massive stars is shorter than the MSTs of random subsets of cluster stars, the cluster is mass segregated. The ONC is mass segregated (see Hillenbrand & Hartmann 1998), and the same signature was found by Sana et al (2010) in Trumpler 14

Methods

Results

Discussion

Conclusion