Pulsating B stars in the Scorpius-Centaurus Association with TESS

Abstract

We study 119 B stars located in the Scorpius-Centaurus Association using data from NASA's TESS Mission. We see pulsations in 81 stars (68%) across the full range of effective temperatures. In particular, we confirm previous reports of low-frequency pulsations in stars whose temperatures fall between the instability strips of SPB stars (slowly pulsating B stars) and $\delta$ Scuti stars. By taking the stellar densities into account, we conclude that these cannot be p modes and confirm previous suggestions that these are probably rapidly-rotating SPB stars. We also confirm that they follow two period-luminosity relations that are consistent with prograde sectoral g modes that are dipole ($l=m=1$) and quadrupole ($l=m=2$), respectively. One of the stars ($\xi^2$ Cen) is a hybrid pulsator that shows regular spacings in both g and p modes. We confirm that $\alpha$ Cru has low-amplitude p-mode pulsations, making it one of the brightest $\beta$ Cephei stars in the sky. We also find several interesting binaries, including a very short-period heartbeat star (HD 132094), a previously unknown eclipsing binary ($\pi$ Lup), and an eclipsing binary with high-amplitude tidally driven pulsations (HR 5846). The results clearly demonstrate the power of TESS for studying variability in stellar associations.