  We demonstrate how the metallicities of red supergiant (RSG) stars can be
measured from quantitative spectroscopy down to resolutions of ~3000 in the
J-band. We have obtained high resolution spectra on a sample of the RSG
population of h and chi Persei, a double cluster in the solar neighborhood. We
show that careful application of the MARCS model atmospheres returns
measurements of Z consistent with solar metallicity. Using two grids of
synthetic spectra--one in pure LTE and one with NLTE calculations for the most
important diagnostic lines--we measure Z = +0.04 +/- 0.10 (LTE) and Z = -0.04
+/- 0.08 (NLTE) for the sample of eleven RSGs in the cluster. We degrade the
spectral resolution of our observations and find that those values remain
consistent down to resolutions of less than R of 3000. Using measurements of
effective temperatures we compare our results with stellar evolution theory and
find good agreement. We construct a synthetic cluster spectrum and find that
analyzing this composite spectrum with single-star RSG models returns an
accurate metallicity. We conclude that the RSGs make ideal targets in the near
infrared for measuring the metallicities of star forming galaxies out to 7-10
Mpc and up to ten times farther by observing the integrated light of unresolved
super star clusters.
