2019AstBu..74..475K

We present the results of long-term spectral monitoring of yellow hypergiants (YHGs) of northern hemisphere with a R > 60 000 resolution. The spectra of these F-G stars of extreme 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 features 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 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 the low-temperature boundary of the Yellow Void.