Physical Properties of the B and Be Star Populations of h and chi Persei

TL;DR

This study analyzes the physical properties of B and Be stars in the h and chi Persei clusters, revealing that Be stars are not rotating near their critical velocity and are more evolved than previously thought.

Contribution

It provides detailed measurements of stellar parameters for B and Be stars in the clusters and compares their rotational velocities and evolutionary states with prior research.

Findings

Most Be stars show emission at observation times.

Be stars are not rotating near critical velocity.

Cluster members are more evolved than previously estimated.

Abstract

We present a study of the B and Be star populations of the Double Cluster h and chi Persei. Blue optical spectroscopy is used to first measure projected rotational velocity, V sin i, effective surface temperature, T_eff, and surface gravity, log g, for B-type sample stars, while available Stromgren photometry is used to calculate T_eff and log g for the Be stars showing emission. In our sample of 104 objects for which we measured these stellar parameters, 28 are known or proposed Be stars. Of these Be stars, 22 show evidence of emission at the times of our observations, and furthermore, we find evidence in our data and the literature for at least 8 transient Be stars in the clusters. We find that the Be stars are not rotating near their critical velocity, contrary to the results of studies of similar open clusters. We compare the results of our analysis with other previous studies, and find that the cluster members are more evolved than found by Huang & Gies but still retain much of their initial rotational angular momentum.