Detection of new eruptions in the Magellanic Clouds luminous blue variables R 40 and R 110^★

¹ Observatório Nacional, Rua General José Cristino, 77, São Cristóvão, Rio de Janeiro 20921-400, Brazil
e-mail: juliocampagnolo@on.br
² Laboratory of Observational Astrophysics, Saint Petersburg State University, Universitetski pr. 28, 198504 Saint Petersburg, Russia
³ Astronomický ústav, Akademie věd České republiky, Fričova 298, 251 65 Ondřejov, Czech Republic
⁴ Tartu Observatory, 61602 Tõravere, Tartumaa, Estonia

Received: 16 August 2017
Accepted: 3 November 2017

Abstract

We performed a spectroscopic and photometric analysis to study new eruptions in two luminous blue variables (LBVs) in the Magellanic Clouds. We detected a strong new eruption in the LBV R40 that reached V ~ 9.2 in 2016, which is around 1.3 mag brighter than the minimum registered in 1985. During this new eruption, the star changed from an A-type to a late F-type spectrum. Based on photometric and spectroscopic empirical calibrations and synthetic spectral modeling, we determine that R 40 reached T_eff = 5800–6300 K during this new eruption. This object is thereby probably one of the coolest identified LBVs. We could also identify an enrichment of nitrogen and r- and s-process elements. We detected a weak eruption in the LBV R 110 with a maximum of V ~ 9.9 mag in 2011, that is, around 1.0 mag brighter than in the quiescent phase. On the other hand, this new eruption is about 0.2 mag fainter than the first eruption detected in 1990, but the temperature did not decrease below 8500 K. Spitzer spectra show indications of cool dust in the circumstellar environment of both stars, but no hot or warm dust was present, except by the probable presence of PAHs in R 110. We also discuss a possible post-red supergiant nature for both stars.