2006/12/01 by G. Houdek, D. O. Gough · 146 citations
Physics and Astronomy · #Adiabatic process #Astronomy and Astrophysical Research #Exponent #Helium #Ionization #Oscillation (cell signaling) #Signature (topology) #Solar and Space Plasma Dynamics #Stellar, planetary, and galactic studies #Superposition principle #astro-ph
paper · pdf · doi:10.1111/j.1365-2966.2006.11325.x
published in Monthly Notices of the Royal Astronomical Society 375(3), 861-880 (Oxford University Press) · 22 pages, 16 figures, accepted by MNRAS on 21 November 2006
arxiv created 2006/12/01 · openalex publication_date 2007/02/02 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We investigate the influence of the ionization of helium on the low-degree acoustic oscillation frequencies in model solar-type stars. The signature in the oscillation frequencies characterizing the ionization-induced depression of the first adiabatic exponent is a superposition of two decaying periodic functions of frequency , with 'frequencies' that are approximately twice the acoustic depths of the centres of the He I and He II ionization regions. That variation is probably best exhibited in the second frequency difference 2 n,l n-1,l -2 n,l + n+1,l . We show how an analytic approximation to the variation of leads to a simple representation of this oscillatory contribution to 2 which can be used to characterize the variation, our intention being to use it as a seismic diagnostic of the helium abundance of the star. We emphasize that the objective is to characterize , not merely to find a formula for 2 that reproduces the data.