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Seismic Diagnostics of Mixing Beyond the Convective Core in Intermediate Mass Main-Sequence Stars

Popielski B. L., Dziembowski W. A.

Acta Astronomica

2005

Vol. 55, No. 2

177--193

We study prospects for seismic sounding the layer of a partial mixing above the convective core in main-sequence stars with masses in the 1.2-1.9 Msolar range. There is an initial tendency to increase of the convective core mass in such stars and this leads to ambiguities in modeling. Solar-like oscillations are expected to be excited in such objects. Frequencies of such oscillations provide diagnostics, which are sensitive to the structure of the innermost part of the star and they are known as the small separations. We construct evolutionary models of stars in this mass range assuming various scenarios for element mixing, which includes formation of element abundance jumps, as well as semiconvective and overshooting layers. We find that the three point small separations employing frequencies of radial and dipole modes provide the best probe of the element distribution above the convective core. With expected accuracy of frequency measurement from the space experiments, a discrimination between various scenarios should be possible.

Petersen Diagram for RRd Stars in the Magellanic Clouds

Popielski B. L., Dziembowski W. A., Cassisi S.

Acta Astronomica

2000

Vol. 50, No. 4

491--507

RRd stars from the Magellanic Clouds form a well-defined band in the Petersen diagram. We explain this observed band with our evolutionary and pulsation calculations with assumed metallicity [Fe/H]=(-2,-1.3). Vast majority of RRd stars from LMC is confined to a narrower range of (-1.7,-1.3). The width of the band, at specified fundamental mode period, may be explained by mass spread at given metallicity. The shape of the band reflects the path of RRd stars within the RR Lyr instability strip. We regard the success in explaining the Petersen diagram as a support for our evolutionary models, which yield mean absolute magnitude in the mid of the instability strip, ⟨MV⟩, in the range 0.4 to 0.65 mag implying distance modulus to the LMC of 18.4 mag.