New luminous blue variable candidates in the NGC 247 galaxy

Abstract

We search for luminous blue variable (LBV) stars in galaxies outside the Local Group. Here we present a study of two bright Hα sources in the NGC 247 galaxy. Object j004703.27-204708.4 (M_V = -9.08 ± 0.15 mag) shows the spectral lines typical for well-studied LBV stars: broad and bright emission lines of hydrogen and helium He I with P Cyg profiles, emission lines of iron Fe II, silicon Si II, nitrogen N II and carbon C II, forbidden iron [Fe II] and nitrogen [N II] lines. The variability of the object is ΔB = 0.74 ± 0.09 mag and ΔV = 0.88 ± 0.09 mag, which makes it a reliable LBV candidate. The star j004702.18-204739.93 (M_V = -9.66 ± 0.23 mag) shows many emission lines of iron Fe II, forbidden iron lines [Fe II], bright hydrogen lines with broad wings, and also forbidden lines of oxygen [O I] and calcium [Ca II] formed in the circumstellar matter. The study of the light curve of this star did not reveal significant variations in brightness (ΔV = 0.29 ± 0.09 mag). We obtained estimates of interstellar absorption, the photosphere temperature, as well as bolometric magnitudes $M_\text{bol}=-10.5^{+0.5}_{-0.4}$ and $M_\text{bol}=-10.8^{+0.5}_{-0.6}$, which correspond to bolometric luminosities $\log (L_\text{bol}/{\rm L}_{\odot })=6.11^{+0.20}_{-0.16}$ and $6.24^{+0.20}_{-0.25}$ for j004703.27-204708.4 and j004702.18-204739.93, respectively. Thus, the object j004703.27-204708.4 remains a reliable LBV candidate, while the object j004702.18-204739.93 can be classified as a B[e]-supergiant.