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

TL;DR

Fast yellow pulsating supergiants (FYPS) are a newly identified class of evolved massive stars that may represent post-red supergiant objects, providing insights into massive star evolution and supernova progenitors.

Contribution

This study identifies and characterizes FYPS in the Magellanic Clouds, establishing their luminosity and temperature ranges, and linking them to post-red supergiant evolutionary stages.

Findings

FYPS occupy regions above log L/L_sun ≈ 5.0 in the HR diagram.

FYPS are associated with initial masses of 18-20 M_sun.

Pulsation frequencies vary with temperature, showing a transition at intermediate temperatures.

Abstract

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 of pulsating evolved massive stars, these objects have incredible potential to change our understanding of the structure and evolution of massive stars. Here we examine the lightcurves of a sample of 126 cool supergiants in the Magellanic Clouds observed by the Transiting Exoplanet Survey Satellite (\tess~) in order to identify pulsating stars. After making quality cuts and filtering out contaminant objects, we examine the distribution of pulsating stars in the Hertzprung-Russel (HR) diagram, and find that FYPS occupy a region above $\log L/L_\odot \gtrsim 5.0$. This luminosity boundary corresponds to stars with initial masses of $\sim$18-20 $M_\odot$, 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. Finally, we characterize the behavior of FYPS pulsations as a function of their location in the HR diagram. We find low frequency pulsations at higher effective temperatures, higher frequency pulsations at lower temperatures, with a transition between the two behaviors at intermediate temperatures. The observed properties of FYPS make them fascinating objects for future theoretical study.