Researchers have reported new eruption events in two blue variables - R 40 and R 110, residing in the territory of the Magellan Clouds. This finding can shed light on the final stages of the stellar evolution process.
Bright blue variables (LBV), which are also called S Golden Fish variables, are rare and unstable massive evolving stars. They are characterized by strong photometric and spectral variability associated with temporary eruptions. So far, within the Milky Way and the Local Group galaxies, there are approximately 40 LBVs in existence.
But there is still little information about the cause of the eruptions in the LBV. There are suggestions that the cause is fast rotation, radiation and turbulent pressure, internal dynamic mechanisms, duality, or a combination of these causes. The exact culprit can be found only in studying the events of the eruption.
The spectral change of R 40 is noticeable in the spectra taken from 2002 (above) to 2016 (below). Changes from late B / early A-type to late F-type spectrum can be considered, indicating a new eruption. The HD 54605 spectrum (F8Ia) is also listed for comparison. Therefore, the researchers were pleased with the new eruptions in R 40 and R 110. The first is located in the Small Magellanic Cloud, 16 times the solar mass and 280 times larger. R 110 is ahead of the sun by a radius 300 times, 10 times more massive and lives in the Large Magellanic Cloud.
Scientists used the FEROS optical spectrograph on the 2.2-meter telescope at the La Silla Observatory (Chile). The analysis shows that both LBVs experience constant eruptions. In R 40, it reached a value of 9.2 in 2016, which is 1.4 million times brighter than the minimum recorded in 1985. Because of this, the temperature of the variable dropped to 6100 K, and it became the coldest among the well-known LBVs.
The maximum value of R 110 reached 9.9 in 2011. The new eruption was weaker than the 1994 event. The temperature dropped to 8,500 K. Astronomers note that more observations will be needed to determine the frequency of eruptions.