The Properties of Fast Yellow Pulsating Supergiants: FYPS Point the Way to Missing Red Supergiants

Fast yellow pulsating supergiants (FYPS) are a recently-discovered class of evolved massive pulsator. As candidate post-red supergiant objects, and one of the few classes evolved massive pulsators, these objects have incredible potential to change our understanding of the structure and evolution of massive stars. Here we use data from the Transiting Exoplanet Survey Satellite (TESS) in order to examine the distribution of pulsating stars in the upper Hertzprung-Russel (HR) diagram. We find that FYPS occupy a region above logL/L⊙≳5.0, corresponding to stars with initial masses ≳18-20 M⊙, consistent with the most massive red supergiant progenitors of supernovae (SNe) II-P, as well as the observed properties of SNe IIb progenitors. This threshold is in agreement with the picture that FYPS are post-RSG stars. The observed properties of FYPS make them fascinating objects for future theoretical study.