Main-Seqence Fitting Distance to the sigma Ori Cluster

TL;DR

This paper estimates the distance to the sigma Ori cluster using main sequence fitting, providing a more precise measurement that refines previous estimates and informs its age and properties.

Contribution

It introduces a main sequence fitting method applied to cluster members to accurately determine the sigma Ori cluster's distance.

Findings

Estimated distance of 420+/-30 pc using main sequence fitting.

Cluster age determined to be 2-3 million years.

Distance as close as 350 pc is inconsistent with observations.

Abstract

The sigma Ori cluster is an unbound aggregate of a few hundred young, low-mass stars centered on the multiple system sigma Ori. This cluster is of great interest because it is at an age when roughly half of the stars have lost their protoplanetary disks, and the cluster has a very large population of brown dwarfs. One of the largest sources of uncertainty in the properties of the cluster is that the distance is not well known. The directly measured Hipparcos distance to sigma Ori AB is 350 (+120,-90) pc. On the other hand, the distance to the Orion OB1b subgroup (of which sigma Ori is thought to be a member), 473+/-40 pc, is far better determined, but it is an indirect estimate of the cluster's distance. Also, Orion OB1b may have a depth of 40 pc along our line of sight. We use main sequence fitting to 9 main sequence cluster members to estimate a best fit distance of 420+/-30 pc, assuming a metallicity of -0.16+/-0.11 or 444 pc assuming solar metallicity. A distance as close as 350 pc is inconsistent with the observed brightnesses of the cluster members. At the best fit distance, the age of the cluster is 2-3 Myrs.