The incidence of LBV variability in the Large Magellanic Cloud

Context. Luminous blue variables (LBVs) exhibit unique variability features, characterized by episodic outbursts (> 1 mag) accompanied by spectroscopic changes (S Dor variables). The question of whether all massive stars undergo an LBV-like phase during their evolution or whether LBVs are exotic phenomena remains a matter of debate. Aims. We aim to quantify the incidence of LBV-like variability in the blue supergiant (BSgs) population of the Large Magellanic Cloud (LMC) using the OGLE survey. Methods. We extended the work of previous studies focused on the Small Magellanic Cloud (SMC) to the LMC, examining the light curves of 87 BSgs (out of 254 known BSgs) spanning timescales of 20 years, along with 37 objects across a three-year timescale for aperiodic variations resembling known S Dor variables. Results. One blue supergiant, [ST92] 4-13 displays S Dor type photometric variations. Newly acquired spectra for this object reveal a potential change in spectral type, compared to the literature classification. However, based on its spectral characteristics and low luminosity and mass, we do not currently classify it as an LBV. Conclusions. Our study highlights the need to classify bona fide LBVs as stars undergoing both photometric and spectroscopic variations. Based on currently known stellar population of S Dor variables in the LMC, the lifetime of the S Dor phase is at most ∼103 yr. This finding is in agreement with our duty cycle study based on OGLE data in the SMC. This is several orders of magnitude shorter than what has been reported in the literature. Our discovery of LBV-like variability at low luminosities potentially suggests that S Dor variations could arise from Eddington limit-related physics over a wide range of stellar masses, rather than being linked to a unique evolutionary stage.