Gravity mode offset and properties of the evanescent zone in red-giant stars

Abstract

The wealth of asteroseismic data for red-giant stars and the precision with which these data have been observed over the last decade calls for investigations to further understand the internal structures of these stars. The aim of this work is to validate a method to measure the underlying period spacing, coupling term and mode offset of pure gravity modes that are present in the deep interiors of red-giant stars. We subsequently investigate the physical conditions of the evanescent zone between the gravity mode cavity and the pressure mode cavity. We implement an alternative mathematical description to analyse observational data and to extract the underlying physical parameters that determine the frequencies of mixed modes. This description takes the radial order of the modes explicitly into account, which reduces its sensitivity to aliases. Additionally, and for the first time, this method allows us to constrain the gravity mode offset for red-giant stars. We determine the period spacing and the coupling term for the dipole modes within a few percent of literature values. Additionally, we find that the gravity mode offset varies on a star by star basis and should not be kept fixed in the analysis. Furthermore, we find that the coupling factor is logarithmically related to the physical width of the evanescent region normalised by the radius at which the evanescent zone is located. Finally, the local density contrast at the edge of the core of red giant branch models shows a tentative correlation with the offset. (abstract abriged)

accepted for publication in A&A

References in corpus (13)

• Modules for Experiments in Stellar Astrophysics (MESA)
• Mixed modes in red giants: a window on stellar evolution
• Period spacings in red giants II. Automated measurement
• Giant star seismology
• Bayesian peak bagging analysis of 19 low-mass low-luminosity red giants observed with Kepler
• Internal rotation of the red-giant star KIC 4448777 by means of asteroseismic inversion
• Structural glitches near the cores of red giants revealed by oscillations in g-mode period spacings from stellar models
• Period spacings in red giants; III. Coupling factors of mixed modes
• Kepler red-clump stars in the field and in open clusters: constraints on core mixing
• Testing the asymptotic relation for period spacings from mixed modes of red giants observed with the Kepler mission
• Verification of Asymptotic Relation for Mixed Modes in Red Giant Stars
• Testing the cores of first ascent red-giant stars using the period spacing of g modes
• Automated determination of g-mode period spacing of red-giant stars

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