Asteroseismology of hot subdwarf B stars observed with TESS: discovery of two new gravity mode pulsating stars

TL;DR

This study uses TESS data to discover and analyze gravity mode pulsations in two hot subdwarf B stars, identifying their pulsation modes, rotation periods, and stellar parameters through asteroseismology.

Contribution

It presents the first detailed asteroseismic analysis of two long-period pulsating subdwarf B stars observed with TESS, including mode identification and rotation period estimation.

Findings

Over 40 pulsation modes detected in each star.

Identification of dipole mode sequences and mean period spacings.

Rotation period of approximately 64 days for TIC033834484.

Abstract

TIC033834484 and TIC309658435 are long-period pulsating subdwarf B star, which were observed extensively (675 and 621 days, respectively) by the Transiting Exoplanet Survey Satellite (TESS). The high-precision photometric light curve reveals the presence of more than 40 pulsation modes including both stars. All the oscillation frequencies that we found are associated with gravity (g)-mode pulsations, with frequencies spanning from 80 $\mu$Hz (2 500 s) to 400 $\mu$Hz (12 000 s). We utilize the asteroseismic tools including asymptotic period spacings and rotational frequency multiplets in order to identify the pulsational modes. We found dipole (l = 1) mode sequences for both targets and calculate the mean period spacing of dipole modes ($\Delta P_{l=1}$), which allows us to identify the modes. Frequency multiplets provide a rotation period of about 64 d for TIC033834484. From follow-up ground-based spectroscopy, we find that TIC\,033834484 has an effective temperature of 24 210 K (140), a surface gravity of logg = 5.28 (03) and TIC309658435 has an effective temperature of 25 910 K (150), a surface gravity of logg = 5.48 (03).