Astronomy and Astrophysics – Astrophysics
Scientific paper
Feb 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...282...73a&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 282, no. 1, p. 73-85
Astronomy and Astrophysics
Astrophysics
25
Seismology, Stellar Evolution, Stellar Interiors, Stellar Mass, Stellar Models, Stellar Oscillations, Stellar Structure, Approximation, Asymptotic Methods, Mathematical Models, Polynomials
Scientific paper
Stars more massive than about 1.2 solar mass are characterized by a convective core, which induces at its frontier a rapid variation of the density, sound speed and Brunt-Vaisala frequency, close to a discontinuity. For three stars of 1, 1.5 and 2 solar mass we have studied the properties of p-mode frequencies of high radial order and low degree, and we present results on the effects on p-mode oscillations of some rapid variations of the internal structure. We first point out the difficulties of the classical asymptotic theory to represent with accuracy the p-mode spectrum of the stars considered. We compare the numerical frequencies with asymptotic and polynomial approximations obtained from fits. The variation of the derived global coefficients characterizing the p-mode spectrum along the evolutionary tracks has been estimated; it would help to separate the effects of age and mass of intermediate-mass stars. The sensitivity of these coefficients to stellar parameters substantially depends on the stellar mass and must be considered for asteroseismic calibration. The effects of rapid variations in the stellar internal structure are finally considered. An asymptotic formula taking into account the rapid variation of the sound speed at the convective core boundary of the 1.5 and 2 solar mass stars predicts an oscillatory behavior of the frequencies with a very large period. We also show that the second frequency difference delta2nu = nun, l - 2nun-1, l + nun-2, l exhibits a substantial oscillation which corresponds to the region of the He II ionization of the 1, 1.5 and 2 solar mass stars.
Audard N.
Provost Janine
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