On P-mode oscillations in stars from 1M _⊙ to 2M _⊙

Abstract

The structure of stars more massive than about 1.2M _⊙ is characterized by a convective core. We have studied the evolution with age and mass of acoustic frequencies if high radial ordern and low degree ℓ for models of stars of 1, 1.5 and 2M _⊙. Using a polynomial approximation for the frequency, the p-mode spectrum can be characterized by derived global asteroseimic coefficients, i.e. the mean separationv ₀∼v _n,ℓ −v _n,−1,ℓ and the small frequency separationΔv _0,2∼v _n,ℓ=0 −v _n,−1,ℓ=2 . The diagram(v ₀,Δ(v _0,2/v ₀ plotted along the evolutionary tracks would help to separate the effects of age and mass. We study of sensitivity of these coefficients and other observable quantities, like the radius and luminosity, the stellar parameters in the vicinity of 1M _⊙ and 2M _⊙; this sensitivity substantially depends on the stellar mass and must be taken into account for asteroseismic calibration of stellar clusters. Considering finally some rapid variations of the internal structure, we show that the second frequency differenceδ₂ v=v _n,ℓ −2v _n,−1,ℓ +v _n,−2,ℓ exhibits and oscillatory behaviour well related to the rapid variation of the adiabatic exponent γ in the HeII ionization zone.

A more complete discussion is given in Audard N, Provost J, ‘Seismological properties of intermediate-mass stars’,A&A, 1993, in press.