# Physical properties of the first spectroscopically confirmed red supergiant stars in the Sculptor Group galaxy NGC 55

## TL;DR

This study spectroscopically confirms the first red supergiant stars in NGC 55, estimates their stellar parameters and metallicities, and compares their properties to RSGs in other environments, enhancing understanding of low-metallicity galaxies.

## Contribution

It provides the first spectroscopic confirmation of RSGs in NGC 55 and offers independent metallicity gradient estimates using advanced stellar models.

## Key findings

- Confirmed RSGs in NGC 55 through spectroscopy
- Estimated stellar parameters and metallicities consistent with low-metallicity environment
- Derived metallicity gradient aligns with previous hot star studies

## Abstract

We present K-band Multi-Object Spectrograph (KMOS) observations of 18 Red Supergiant (RSG) stars in the Sculptor Group galaxy NGC 55. Radial velocities are calculated and are shown to be in good agreement with previous estimates, confirming the supergiant nature of the targets and providing the first spectroscopically confirmed RSGs in NGC 55. Stellar parameters are estimated for 14 targets using the $J$-band analysis technique, making use of state-of-the-art stellar model atmospheres. The metallicities estimated confirm the low-metallicity nature of NGC 55, in good agreement with previous studies. This study provides an independent estimate of the metallicity gradient of NGC 55, in excellent agreement with recent results published using hot massive stars. In addition, we calculate luminosities of our targets and compare their distribution of effective temperatures and luminosities to other RSGs, in different environments, estimated using the same technique.