Search for LBVs in the Local Volume galaxies: Study of four stars in NGC 4449

Abstract

We continue to search for LBV stars in galaxies outside the Local Group. In this work, we have investigated four luminous stars in NGC 4449. Multiple spectral observations carried out for J122810.94+440540.6, J122811.70+440550.9, and J122809.72+440514.8 revealed the emission features in their spectra that are characteristic of LBVs. Photometry showed noticeable brightness changes of J122809.72+440514.8 (ΔI = 0.69 ± 0.13m) and J122817.83+440630.8 (ΔR = 2.15 ± 0.13m), while the variability of J122810.94+440540.6 and J122811.70+440550.9 does not exceed 0.3m regardless of the filter. We have obtained estimates of the interstellar reddening, photosphere temperatures, and bolometric luminosities log (LBol/L⊙) ≈ 5.24-6.42. Using the cmfgen code, we have modelled the spectrum of the cold state of J122809.72+440514.8 ($T_{\text{eff}}=9300\,$ K) and have obtained possible value of the mass-loss rate $\dot{M} = 5.2\times 10^{-3}\, \mathrm{M}_{\odot }\, \mathrm{yr}^{-1}$. Based on the observational properties, J122809.72+440514.8 and J122817.83+440630.8 were classified as LBVs, while the other two stars were classified as LBV candidates or B[e]-supergiants candidates.