Photometric and spectroscopic analysis of LBV candidate J004341.84+411112.0 in M31

Abstract

We study Luminous Blue Variable (LBV) candidate J004341.84+411112.0 in the Andromeda galaxy. We present optical spectra of the object obtained with the 6-m telescope of SAO RAS. The candidate shows typical LBV features in its spectra: broad and strong hydrogen lines and the He I lines with P Cigni profiles. Its remarkable spectral resemblance to the well known LBV P Cygni suggests a common nature of the objects and supports LBV classification of J004341.84+411112.0. We estimate the temperature, reddening, radius and luminosity of the star using its spectral energy distribution. Obtained bolometric luminosity of the candidate ($M_{\text{bol}}=-10.41\pm 0.12$ mag) is quite similar to those of known LBV stars in the Andromeda galaxy. We analysed ten year light curve of the object in $R$ filter. The candidate demonstrates photometric variations of the order of 0.4 mag, with an overall brightness increasing trend $\hat{I}”R>0.1$ mag. Therewith, the corresponding colour variations of the object are fully consistent with LBV behavior when a star become cooler and brighter in the optical spectral range with a nearly constant bolometric luminosity. LBV-type variability of the object, similarity of its spectrum and estimated luminosity to those of known LBVs allows us to classify J004341.84+411112.0 as a LBV.