Detection of new eruptions in the Magellanic Clouds LBVs R 40 and R 110

TL;DR

This study reports new eruptions in two LBVs in the Magellanic Clouds, analyzing their spectroscopic and photometric changes, chemical enrichment, and circumstellar dust, revealing insights into their eruption behavior and evolutionary status.

Contribution

The paper presents the first detailed spectroscopic and photometric analysis of eruptions in LBVs R 40 and R 110, including temperature estimates and circumstellar dust characteristics.

Findings

R 40 experienced a strong eruption reaching V~9.2 in 2016.

R 110 had a weaker eruption in 2011 with V~9.9.

Both stars show signs of nitrogen and s-process element enrichment.

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 $V \sim 9.2$ 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 $T_{\mathrm{eff}} = 5800-6300$~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 $V \sim 9.9$ 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.