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Massive B-type pulsators in low-metallicity environments

By C. Karoff, T. Arentoft, L. Glowienka, C. Coutures, T. B. Nielsen, G. Dogan, F. Grundahl and H. Kjeldsen

Abstract

Massive B-type pulsators such as β Cep and slowly pulsating B (SPB) stars pulsate due to layers of increased opacity caused by partial ionization. The increased opacity blocks the energy flux to the surface of the stars which causes the layers to rise and the opacity to drop. This cyclical behavior makes the star act as a heat engine and the star will thus pulsate. For β Cep and SPB stars the increased opacity is believed to be caused by partial ionization of iron and these stars should therefore contain non-insignificant quantities of the metal. A good test of this theory is to search for β Cep and SPB stars in low-metallicity environments. If no stars are found the theory is supported, but on the other hand if a substantial number of β Cep and SPB stars are found in these environments then the theory is not supported and a solutions needed. With a growing number of identified β Cep and SPB stars in the low-metallicity Magellanic Clouds we seem to be left with the second case. We will in this context discuss recent findings of β Cep and SPB stars in the Magellanic Clouds and some possible solutions to the discrepancy between these observations and the theory. We also describe an ambitious project that we have initiated on the Small Magellanic Cloud open cluster NGC 371 which will help to evaluate these solutions. Session: Observed frequencies in pulsating massive stars Individual Objects: NGC 3712 Massive B-type pulsators in low-metallicity environments The Problem Though the number of β Cep and SPB stars is predicted to be very limited in the Magellanic Clouds due to the reduced metallicity in these environments

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