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

Abstract

Fast yellow pulsating supergiants (FYPS) are a recently discovered class of evolved massive pulsators. As candidate 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 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 ⊙ ≳ 5.0 . This luminosity boundary corresponds to stars with initial masses of ∼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. 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, and 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.

Yellow Supergiants and Post-red Supergiant Evolution in the Large Magellanic Cloud

“…These fast yellow pulsating supergiants (FYPS) have luminosites above 10 5 L e corresponding to stars with initial masses above 18-20 M e . Dorn-Wallenstein et al (2022) thus argue that the FYPS are consistent with post-red supergiant evolution.…”

“…Consequently, we used the color excess for each individual star to derive the K-band extinction and the adopted temperature from the spectral type for the K-band bolometric correction. The resulting luminosities average 0.14 higher in Log L/L e than those in Neugent et al (2012) andDorn-Wallenstein et al (2022).…”

“…The SEDs for the six YSGs with circumstellar dust are shown in Figure 1. Although the YSGs or F-type supergiants are the focus of this work, we examined the infrared fluxes for the high-luminosity A-type supergiants and FYPS in Dorn-Wallenstein et al (2022) for CS dust and found only one marginal case, HD 269661 (A0 Ia0e), which is also an emission-line star. Two of the less luminous pulsators (log L/L e < 5.0) show evidence for weak circumstellar dust, and none of the nonpulsators have a long wavelength excess due to dust.…”

“…The fate of RSGs with initial masses above 20 M e is debated. For example, in a recent paper Pedersen & Bell (2023) argued that the FYPS were the result of contamination in the TESS data, but Dorn-Wallenstein et al (2022) identified likely contaminated stars and removed them from their sample. Six of the nine stars have circumstellar dust, which distinguishes them from the other YSGs.…”

“…HD 269651 is listed as F0 I inDorn-Wallenstein et al (2022), but the description of its spectrum and published photometry supports the A2 Ia0 type(Ardeberg et al 1972). …”