A new class of pulsating hot subdwarfs
  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.
