An article published in the journal “Astronomy & Astrophysics” reports the results of a study on some yellow hypergiants and in particular Rho Cassiopeiae, of which observations are available that go back to 1885. A team of researchers also examined observations of HR 8752, HR 5171A, and HD 179821 with a focus on the outbursts and the resulting variability that characterize yellow hypergiants. This study shows that the pulsations of Rho Cassiopeiae, or simply Rho Cas, become more intense when it approaches an explosive event. 138 years of observations have led to modeling Rho Cas’s behavior and predicting its future.

Yellow hypergiants are considered stars at the end of their normal life that are about to contract and probably within a few million years will be reduced to a white dwarf. They are going through a phase that is short in astronomical terms with quick changes that are visible even in the course of a human lifetime.

Observations dating back to the 19th century have already been used to study another yellow hypergiant, U Monocerotis. Rho Cas now represents an even more extreme case of using old observations, as the authors of this study assembled a mass of data spanning about 138 years. In 2023, images were also captured with the CHARA (Center for High Angular Resolution Astronomy) array and used for another study published in “The Astrophysical Journal”.

This new study on yellow hypergiants also used spectroscopic data combined with photometric observations of Rho Cas obtained between 1962 and 2020. This is a new methodology developed by the authors to obtain a more accurate analysis of these extreme stars.

The analysis of the collected data indicates that pulsations play a crucial role in triggering recurrent outbursts in yellow hypergiants. In the case of Rho Cas, six of them were recorded at intervals of 10, 41, 40, 14, and 13 years. The comparison with HR 8752 suggests that Rho Cas will become stable around 2045.

This study attempted to find a pattern in the apparently chaotic behavior of yellow hypergiants. The availability of observations conducted over a very long period allowed for an accurate analysis to create a model of the pulsations and outbursts. The result is a prediction that will have to be verified and, considering that it will take about twenty years to test it, it will be possible to refine it and apply it to other stars in that particular phase.