Acoustic Signatures of the Helium Core Flash

All evolved stars with masses M <~ 2 M _⊙ undergo an initiating off-center helium core flash in their M_c ≈ 0.48 M _⊙ He core as they ascend the red giant branch (RGB). This off-center flash is the first of a few successive helium shell subflashes that remove the core electron degeneracy over 2 Myr, converting the object into a He-burning star. Though characterized by Thomas over 40 years ago, this core flash phase has yet to be observationally probed. Using the Modules for Experiments in Stellar Astrophysics (\texttt {MESA}) code, we show that red giant asteroseismology enabled by space-based photometry (i.e., Kepler and CoRoT) can probe these stars during the flash. The rapid (lsim 10⁵ yr) contraction of the red giant envelope after the initiating flash dramatically improves the coupling of the p-modes to the core g-modes, making the detection of l = 1 mixed modes possible for these 2 Myr. This duration implies that 1 in 35 stars near the red clump in the H-R diagram will be in their core flash phase. During this time, the star has a g-mode period spacing of ΔP _g ≈ 70-100 s, lower than the ΔP _g ≈ 250 s of He-burning stars in the red clump, but higher than the RGB stars at the same luminosity. This places them in an underpopulated part of the large frequency spacing (Δν) versus ΔP _g diagram that should ease their identification among the thousands of observed red giants.