A new class of pulsating hot subdwarfs

• Published in: arXiv.org 2019-06
• Main Authors: Kupfer, Thomas, Bauer, Evan B, Burdge, Kevin B, Bellm, Eric C, Bildsten, Lars, Fuller, Jim, Hermes, J J, Kulkarni, Shrinivas R, Prince, Thomas A, Jan van Roestel, Dekany, Richard, Duev, Dmitry A, Feeney, Michael, Giomi, Matteo, Graham, Matthew J, Kaye, Stephen, Laher, Russ R, Masci, Frank J, Porter, Michael, Riddle, Reed, Shupe, David L, Smith, Roger M, Soumagnac, Maayane T, Szkody, Paula, Ward, Charlotte
• Format: Article
• Language: English
• Subjects: Amplitudes; Fourier transforms; Helium; Pulsation; Radial velocity; Stellar oscillations; Subdwarf stars; White dwarf stars
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1906.00979

Using high-cadence observations from the Zwicky Transient Facility at low Galactic latitudes, we have discovered a new class of pulsating, hot, compact stars. We have found four candidates, exhibiting blue colors (\(g-r\leq-0.1\) mag), pulsation amplitudes of \(>5\%\), and pulsation periods of \(200 - 475\) sec. Fourier transforms of the lightcurves show only one dominant frequency. Phase-resolved spectroscopy for three objects reveals significant radial velocity, T\(_{\rm eff}\) and log(g) variations over the pulsation cycle, consistent with large amplitude radial oscillations. The mean T\(_{\rm eff}\) and log(g) for these stars are consistent with hot subdwarf B (sdB) effective temperatures and surface gravities. We calculate evolutionary tracks using MESA and adiabatic pulsations using GYRE for low-mass helium-core pre-white dwarfs and low mass helium-burning stars. Comparison of low-order radial oscillation mode periods with the observed pulsation periods show better agreement with the pre-white dwarf models. Therefore, we suggest that these new pulsators and Blue Large-Amplitude Pulsators (BLAPs) could be members of the same class of pulsators, composed of young \(\approx0.25-0.35\) M\(_\odot\) helium-core pre-white dwarfs.