Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993mnras.265..588d&link_type=abstract
Monthly Notices of the Royal Astronomical Society, Vol. 265, NO. 3/DEC1, P. 588, 1993
Astronomy and Astrophysics
Astronomy
130
Instabilities - Radiative Transfer - Stars: Early-Type - Stars: Interiors - Stars: Scillations
Scientific paper
We show that the OPAL opacities, in addition to explaining the origin of the pulsations of β Cep stars, also predict the existence of a large region in the main-sequence band at lower luminosities, where high-order g-modes of low harmonic degree l are unstable. The excitation mechanism remains the same, and is due to the usual w-effect acting in the metal opacity bump (T ≍ 2 × 105 K). The new instability domain nearly bridges the gap in spectral types between δ Sct and β Cep stars. The periods of the unstable modes are in the range 0.4-3.5 d for l=1 and 2. We propose that this excitation mechanism causes photometric variability in the slowly pulsating B-type stars (SPB stars), and perhaps in other B stars for which variability in the same period range has been reported.
Typically, a large number of modes are simultaneously unstable in one model. Most of them have l>2. Such modes are not likely to be detected photometrically, but may be visible in line profile changes. The excitation of many high-l modes in a star may also cause a spurious contribution to the rotational υ sin i values.
Sequences of unstable modes at each value of l exhibit a periodically varying departure from equal spacing in period. This feature, first noted in white dwarf g-mode spectra (calculated and measured), is in the present case a probe of the region left behind the shrinking core (the μ-gradient zone). We discuss prospects for and difficulties of SPB-star asteroseismology.
Dziembowski Wojciech A.
Moskalik Pawel
Pamyatnykh Alexey A.
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