# Modelling the Near-IR Spectra of Red Supergiant-dominated Populations

## TL;DR

This paper advances the modeling of near-infrared spectra of young stellar populations dominated by red supergiants, improving parameter determination and population synthesis predictions, with applications to star clusters in M82.

## Contribution

It introduces new methods for fitting RSG spectra with PHOENIX models and enhances population synthesis predictions for young stellar clusters.

## Key findings

- Accurate RSG parameters obtained from near-IR spectral fits.
- Successful reproduction of M82 star cluster spectra from 0.5 to 2.4 micrometers.
- Remaining uncertainties in cluster age estimates.

## Abstract

We report on recent progress in the modelling of the near-IR spectra of young stellar populations, i.e. populations in which red supergiants (RSGs) are dominant. First, we discuss the determination of fundamental parameters of RSGs using fits to their near-IR spectra with new PHOENIX model spectra; RSG-specific surface abundances are accounted for and effects of the microturbulence parameter are explored. New population synthesis predictions are then described and, as an example, it is shown that the spectra of young star clusters in M82 can be reproduced very well from 0.5 to 2.4 micrometers. We warn of remaining uncertainties in cluster ages.