Pulse Timing Discovery of a Three-day Companion to the Hot Subdwarf BPM 36430

• Published in: The Astrophysical journal Vol. 939; no. 1; pp. 57 - 62
• Main Authors: Smith, Bryce A., N. Barlow, Brad, Rosenthal, Benjamin, Hermes, J. J., Schaffenroth, Veronika
• Format: Journal Article
• Language: English
• Published: Philadelphia The American Astronomical Society 01.11.2022; IOP Publishing
• Subjects: Astrophysics; B stars; Binary stars; Center of gravity; Companion stars; Extrasolar planets; Helium; Motion perception; Orbits; Periodic variations; Planet detection; Pulsation; Stellar pulsations; Subdwarf stars; Transit; White dwarf stars
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/ac9384

Abstract Hot subdwarf B stars are core-helium-burning objects that have undergone envelope stripping, likely by a binary companion. Using high-speed photometry from the Transiting Exoplanet Survey Satellite, we have discovered the hot subdwarf BPM 36430 is a hybrid sdBV rs pulsator exhibiting several low-amplitude g -modes and a strong p -mode pulsation. The latter shows a clear, periodic variation in its pulse arrival times. Fits to this phase oscillation imply BPM 36430 orbits a barycenter approximately 10 light-seconds away once every 3.1 days. Using the CHIRON echelle spectrograph on the CTIO 1.5 m telescope, we confirm the reflex motion by detecting a radial-velocity variation with semiamplitude, period, and phase in agreement with the pulse timings. We conclude that a white dwarf companion with minimum mass of ≈0.42 M ⊙ orbits BPM 36430. Our study represents only the second time a companion orbiting a pulsating hot subdwarf or white dwarf has been detected from pulse timings and confirmed with radial velocities.