Red Supergiant Stars as Cosmic Abundance Probes: KMOS Observations in NGC 6822

TL;DR

This study uses near-infrared spectroscopy of red supergiant stars in NGC 6822 to measure metallicity, find a possible abundance gradient, and compare stellar properties across different galaxies, challenging some evolutionary model predictions.

Contribution

It provides new metallicity measurements of RSGs in NGC 6822 using VLT-KMOS and compares these with other stellar populations and models, revealing insights into stellar properties and galaxy evolution.

Findings

Mean metallicity [Z] = -0.52 ± 0.21 in NGC 6822

Possible low-significance abundance gradient within 1 kpc

No significant temperature variation of RSGs with metallicity

Abstract

We present near-IR spectroscopy of red supergiant (RSG) stars in NGC 6822, obtained with the new VLT-KMOS instrument. From comparisons with model spectra in the J-band we determine the metallicity of 11 RSGs, finding a mean value of [Z] = -0.52 $\pm$ 0.21 which agrees well with previous abundance studies of young stars and HII regions. We also find an indication for a low-significance abundance gradient within the central 1 kpc. We compare our results with those derived from older stellar populations and investigate the difference using a simple chemical evolution model. By comparing the physical properties determined for RSGs in NGC 6822 with those derived using the same technique in the Galaxy and the Magellanic Clouds, we show that there appears to be no significant temperature variation of RSGs with respect to metallicity, in contrast with recent evolutionary models.