The Araucaria Project: VLT-spectroscopy of blue massive stars in NGC 55

TL;DR

This study provides the first comprehensive catalog of blue massive stars in NGC 55, using VLT spectroscopy to analyze their properties, velocities, and metallicity distribution, laying groundwork for future detailed modeling.

Contribution

It presents the first census and classification of blue massive stars in NGC 55, along with initial velocity and metallicity analyses, advancing understanding of stellar populations in this galaxy.

Findings

Catalog of 164 blue massive stars in NGC 55.

Radial velocities align with HI rotation curve.

Metallicity distribution similar to the LMC.

Abstract

This is the first paper of a series devoted to studying the population of blue massive stars in NGC 55, a galaxy of the Sculptor group at a distance of about 2 Mpc. We have obtained optical (3300-6210A) low-resolution spectra of blue massive stars with VLT-FORS2, which we have classified with the aid of Milky Way and Magellanic Cloud standard stars. We have developed the first census of massive blue stars in NGC 55. A study of stellar radial velocities shows agreement with existing HI rotational velocity curve work and reveals the presence of one object with peculiar velocity. A qualitative study of the stellar metallicity suggests that its global distribution over NGC 55 is close to that of the LMC, as derived from previous studies. We present a catalogue with 164 classifications of blue massive stars in NGC 55. This catalogue is a first and necessary step for the subsequent quantitative study of blue massive stars in NGC 55 with state-of-the-art models.