# The HST Key Project galaxies NGC 1326A, NGC 1425 and NGC 4548: New variable stars and massive star population

## TL;DR

This study analyzes the massive star populations in three galaxies using Hubble data, identifying thousands of supergiants and discovering new variable stars to understand star formation in different environments.

## Contribution

It provides a detailed census of supergiants and variable stars in three galaxies, employing high-precision photometry and stellar evolution models to explore star formation histories.

## Key findings

- Identified 7640 blue, 2314 yellow, and 4270 red supergiants.
- Discovered 243 new variable star candidates across different supergiant types.
- Estimated star formation histories using stellar evolution models.

## Abstract

Studies on the massive star population in galaxies beyond the Local Group are the key to understand the link between their numbers and modes of star formation in different environments. We present the analysis of the massive star population of the galaxies NGC 1326A, NGC 1425 and NGC 4548 using archival Hubble Space Telescope Wide Field Planetary Camera 2 images in the F555W and F814W filters. Through high precision point spread function fitting photometry for all sources in the three fields we identified 7640 candidate blue supergiants, 2314 candidate yellow supergiants, and 4270 candidate red supergiants. We provide an estimation the ratio of blue to red supergiants for each field as a function of galactocentric radius. Using Modules for Experiments in Stellar Astrophysics (MESA) at solar metallicity, we defined the luminosity function and estimated the star formation history of each galaxy. We carried out a variability search in the V and I filters using three variability indexes: the median absolute deviation, the interquartile range, and the inverse von-Neumann ratio. This analysis yielded 243 new variable candidates with absolute magnitudes ranging from Mv= -4 to -10 mag. We classified the variable stars based on their absolute magnitude and their position on the color-magnitude diagram using the MESA evolutionary tracks at solar metallicity. Our analysis yielded 8 candidate variable blue supergiants, 12 candidate variable yellow supergiants, 21 candidate variable red supergiants, and 4 candidate periodic variables.