Lars Bildsten, Bill Paxton, Kevin Moore, Phillip J. Macias
All evolved stars with masses M <2 solar masses undergo an initiating
off-center helium core flash in their 0.48 solar mass 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 Myrs, 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 (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 (< 100,000 years) 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
Myrs. This duration implies that 1 in 35 stars near the red clump in the HR
diagram will be in their core flash phase. During this time, the star has a
g-mode period spacing of Delta P_g = 70-100 seconds, lower than the Delta
P_g=250 seconds 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 (Delta nu) vs. Delta P_g diagram that should ease their
identification amongst the thousands of observed red giants.
View original:
http://arxiv.org/abs/1111.6867
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