科研之友
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摘要
All evolved stars with masses M less than or similar to 2 M(circle dot) undergo an initiating off-center helium core flash in their M(c) approximate to 0.48 M(circle dot) 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 (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 (less than or similar to 10(5) 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 Delta P(g) approximate to 70-100 s, lower than the Delta P(g) approximate to 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 (Delta nu) versus Delta P(g) diagram that should ease their identification among the thousands of observed red giants.
- 出版日期2012-1-1
- 单位中国科学院理论物理研究所
