Quantitative Spectroscopic J-band Study of Red Supergiants in Perseus OB-1

TL;DR

This study demonstrates that red supergiant stars' metallicities can be accurately measured using J-band spectroscopy at resolutions as low as 3000, enabling metallicity assessments of distant star-forming galaxies.

Contribution

The paper introduces a method for measuring RSG metallicities with moderate spectral resolution and validates its accuracy through synthetic and real spectra analysis.

Findings

Metallicity measurements are consistent with solar values.

Spectral resolution as low as R<3000 is sufficient for accurate measurements.

The method applies to unresolved super star clusters in distant galaxies.

Abstract

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.