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QUANTITATIVE SPECTROSCOPIC J-BAND STUDY OF RED SUPERGIANTS IN PERSEUS OB-1

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 χ 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 non-LTE (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 λ/δλ 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 10 times farther by observing the integrated light of unresolved super star clusters.