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

Thayne Currie, Jesus Hernandez, Jonathan Irwin, Scott J. Kenyon, Susan Tokarz, Zoltan Balog, Ann Bragg, Perry Berlind, Mike Calkins

Published 2009-11-29Version 1

(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.