A New Luminous Blue Variable in the Outskirts of the Andromeda Galaxy

The hot massive luminous blue variables (LBVs) represent an important evolutionary phase of massive stars. Here, we report the discovery of a new LBV—LAMOST J0037+4016 in the distant outskirt of the Andromeda galaxy. It is located in the southwestern corner (a possible faint spiral arm) of M31 with an unexpectedly large projection distance of ∼22 kpc from the center. The optical light curve shows a 1.2 mag variation in V band and its outburst and quiescence phases both last over several years. The observed spectra indicate an A-type supergiant at an epoch close to the outburst phase and a hot B-type supergiant with weak [Fe ii] emission lines at an epoch of much dimmer brightness. The near-infrared color–color diagram further shows that it follows the distribution of Galactic and M31 LBVs rather than B[e] supergiants. All the existing data strongly show that LAMOST J0037+4016 is an LBV. By spectral energy distribution fitting, we find it has a luminosity (4.42 ± 1.64) × 105 L⊙ and an initial mass ∼30 M⊙, indicating its nature of a less luminosity class of LBV.