The Stellar Population of h and chi Persei: Cluster Properties, Membership, and the Intrinsic Colors and Temperatures of Stars

TL;DR

This extensive study of the h and χ Persei clusters combines photometry and spectroscopy of thousands of stars to determine their properties, membership, ages, and intrinsic stellar parameters, providing new insights into their stellar populations.

Contribution

It presents the first comprehensive spectroscopic and photometric membership catalog for the clusters down to M dwarfs and derives a new effective temperature scale for various stellar types.

Findings

At least 13,000 to 20,000 members in the clusters.

Estimated total stellar mass of at least 20,000 solar masses.

Clusters are approximately 14 million years old.

Abstract

(Abridged) From photometric observations of $\sim$ 47,000 stars and spectroscopy of $\sim$ 11,000 stars, we describe the first extensive study of the stellar population of the famous Double Cluster, h and $\chi$ Persei, down to subsolar masses. Both clusters have E(B-V) $\sim$ 0.52--0.55 and dM = 11.8--11.85; the halo population, while more poorly constrained, likely has identical properties. As determined from the main sequence turnoff, the luminosity of M supergiants, and pre-main sequence isochrones, ages for h Persei, $\chi$ Persei and the halo population all converge on $\approx$ 14 Myr. From these data, we establish the first spectroscopic and photometric membership lists of cluster stars down to early/mid M dwarfs. At minimum, there are $\sim$ 5,000 members within 10' of the cluster centers, while the entire h and $\chi$ Persei region has at least $\sim$ 13,000 and as many as 20,000 members. The Double Cluster contains $\approx$ 8,400 M$_{\odot}$ of stars within 10' of the cluster centers. We estimate a total mass of at least 20,000 M$_{\odot}$. We conclude our study by outlining outstanding questions regarding the properties of h and $\chi$ Persei. From comparing recent work, we compile a list of intrinsic colors and derive a new effective temperature scale for O--M dwarfs, giants, and supergiants.