Unity and Diversity of Yellow Hypergiants Family

TL;DR

This study provides a comprehensive spectral analysis of yellow hypergiants, revealing their spectral variability, physical properties, and dynamic instabilities, thereby enhancing understanding of their evolutionary status and atmospheric behavior.

Contribution

It offers long-term high-resolution spectral monitoring data and confirms key aspects of yellow hypergiants' physical and dynamic properties, including instability and evolutionary phase indications.

Findings

Confirmed YHG status of V1427 Aql.

Detected atmospheric stratification in ρ Cas after 2017.

Proved absence of a companion in V509 Cas.

Abstract

We summarize the results of long-term spectral monitoring of yellow hypergiants (YHGs) of northern hemisphere with a R$\ge$60000 resolution. The spectra of these F-G stars of extremely high luminosity, compactly located at the top of the Hertzsprung-Russell diagram revealed a variety of spectral features: various types of H$\alpha$ profile, the presence (or absence) of forbidden and permitted emissions, as well as circumstellar components. Variability of spectral details of various nature is studied. Absolute luminosity, circumstellar envelope expansion rate and amplitude of pulsations are determined. The reliability of the YHG status for V1427 Aql is reliably confirmed; manifestations of a significant dynamic instability of the upper layers of the atmosphere of $\rho$ Cas after the 2017 ejection and stratification of its gas envelope are registered; the lack of companion in the system of the V509 Cas hypergiant is proven; a conclusion is made that the V1302 Aql hypergiant is approaching to the low-temperature boundary of the Yellow Void.