Searching for the brightest stars in galaxies outside the Local Group

Abstract

This paper introduces a technique for searching for bright massive stars in galaxies beyond the Local Group. To search for massive stars, we processed the results of stellar photometry from the Hubble Space Telescope (HST) images using the DAOPHOT and DOLPHOT packages. The results of such searches are demonstrated with examples of the galaxies DDO 68, M94 and NGC 1672. In the galaxy DDO 68, the LBV star changes its brightness, and massive stars in M94 can be identified by excess in the Hα band. For the galaxy NGC 1672, we measure the distance for the first time by the TRGB method, which enabled determining the luminosities of the brightest stars, likely hypergiants, in the young star formation region. So far, we have performed stellar photometry on HST images of 320 northern sky galaxies located at a distance less than 12 Mpc. 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.

Brightest stars of irregular and low-massive spiral galaxies

“…m 2, but sometimes blue background stars do not differ in color from young stars of the studied galaxy, which complicates the search for really bright stars. An example is the metal-poor dwarf galaxy DDO 68, where, in addition to the bright massive LBV star (Luminocity Blue Variable), a brighter blue background star (Tikhonov et al 2021) is visible. That is, the probability for background objects to fall into the sample of candidates for bright massive stars is far from zero.…”