Title: STRUCTURAL GLITCHES NEAR THE CORES OF RED GIANTS REVEALED BY OSCILLATIONS IN G-MODE PERIOD SPACINGS FROM STELLAR MODELS

Abstract

With recent advances in asteroseismology it is now possible to peer into the cores of red giants, potentially providing a way to study processes such as nuclear burning and mixing through their imprint as sharp structural variations—glitches—in the stellar cores. Here we show how such core glitches can affect the oscillations we observe in red giants. We derive an analytical expression describing the expected frequency pattern in the presence of a glitch. This formulation also accounts for the coupling between acoustic and gravity waves. From an extensive set of canonical stellar models we find glitch-induced variation in the period spacing and inertia of non-radial modes during several phases of red giant evolution. Significant changes are seen in the appearance of mode amplitude and frequency patterns in asteroseismic diagrams such as the power spectrum and the échelle diagram. Interestingly, along the red giant branch glitch-induced variation occurs only at the luminosity bump, potentially providing a direct seismic indicator of stars in that particular evolution stage. Similarly, we find the variation at only certain post-helium-ignition evolution stages, namely, in the early phases of helium core burning and at the beginning of helium shell burning, signifying the asymptotic giant branch bump. Based onmore » our results, we note that assuming stars to be glitch-free, while they are not, can result in an incorrect estimate of the period spacing. We further note that including diffusion and mixing beyond classical Schwarzschild could affect the characteristics of the glitches, potentially providing a way to study these physical processes.« less

Authors:

Cunha, M. S.; Avelino, P. P. ^[1]; Stello, D. ^[2]; Christensen-Dalsgaard, J. ^[3]; Townsend, R. H. D., ^[4]

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+ Show Author Affiliations

1. Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto (Portugal)
2. Sydney Institute for Astronomy (SIfA), School of Physics, University of Sydney, NSW 2006 (Australia)
3. Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C (Denmark)
4. Department of Astronomy, University of Wisconsin–Madison, 2535 Sterling Hall, 475 N. Charter Street, Madison, WI 53706 (United States)

Publication Date:

Mon Jun 01 00:00:00 EDT 2015

OSTI Identifier:

22522365

Resource Type:

Journal Article

Journal Name:

Astrophysical Journal

Additional Journal Information:

Journal Volume: 805; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0004-637X

Country of Publication:

United States

Language:

English

Subject:

79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ASYMPTOTIC SOLUTIONS; DIAGRAMS; DIFFUSION; GRAVITY WAVES; HELIUM; LUMINOSITY; MOMENT OF INERTIA; OSCILLATIONS; RED GIANT STARS; STAR EVOLUTION; STAR MODELS; VARIATIONS