Search for LBVs in the Local Volume galaxies: study of two stars in NGC 1156

Abstract

ABSTRACT We continue the search for luminous blue variables (LBVs) in Local Volume galaxies in order to study their fundamental parameters. In this paper, we report the discovery of two new LBVs in the dwarf irregular galaxy NGC 1156. Both stars exhibit spectral variability simultaneously with strong brightness variations: ΔRc = 0.84 ± 0.23m for J025941.21+251412.2 and ΔRc = 2.59 ± 0.10m for J025941.54+251421.8. The bolometric luminosities of the stars are in the range of LBol ≈ (0.8–1.6) × 106 L⊙. These values are corrected for reddening AV ≈ 0.9 and are given for the distance to the galaxy D = 7.0 ± 0.4 Mpc, which we have measured by the tip of the red-giant branch method. Both stars are above the Humphreys–Davidson limit in the region of relatively low temperatures, Teff ≲ 10 kK, on the temperature–luminosity diagram. J025941.54+251421.8 had a temperature below the hydrogen ionization threshold at maximum brightness, exhibiting behaviour very similar to that of the known LBV R71 during its 2012 outburst. We have estimated the masses of the detected LBVs and studied the properties of their stellar environment. We discuss our results within the framework of both a single star and a binary system evolution scenario for LBVs.