Search for the brightest stars in galaxies outside the Local Group

TL;DR

This study develops a technique using Hubble Space Telescope data to identify bright massive stars in galaxies beyond the Local Group, successfully applying it to several galaxies and discovering hypergiants.

Contribution

Introduces a new method combining stellar photometry and Hα excess detection to find massive stars in distant galaxies, including the first distance measurement for NGC1672 via TRGB.

Findings

Identified 53 galaxies with probable hypergiants.

Measured the distance to NGC1672 for the first time.

Detected brightness variability of LBV star in DDO68.

Abstract

This paper shows a technique for searching for bright massive stars in galaxies beyond the Local Group. To search for massive stars, we used the results of stellar photometry of the Hubble Space Telescope images using the DAOPHOT and DOLPHOT packages. The results of such searches are shown on the example of the galaxies DDO68, M94 and NGC1672. In the galaxy DDO68 the LBV star changes its brightness, and in M94 massive stars can be identified by the excess in the H${\alpha}$ band. For the galaxy NGC1672, we measured the distance for the first time by the TRGB method, which made it possible to determine the luminosities of the brightest stars, likely hypergiants, in the young star formation region. So far we have performed stellar photometry of HST images of 320 northern sky galaxies located at a distance below 12Mpc. This allowed us to identify 53 galaxies with probable hypergiants. Further photometric and spectral observations of these galaxies are planned to search for massive stars.