Massive B-type pulsators in low-metallicity environments

TL;DR

This paper investigates the presence of massive B-type pulsators in low-metallicity environments like the Magellanic Clouds to test theories about their pulsation mechanisms related to metal content.

Contribution

It presents observational evidence of beta Cep and SPB stars in low-metallicity environments, challenging existing theories about their dependence on metal abundance.

Findings

Detection of beta Cep and SPB stars in the Magellanic Clouds.

Discussion of potential solutions to the discrepancy between observations and theory.

Initiation of a project on NGC 371 to further evaluate these findings.

Abstract

Massive B type pulsators such as beta 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 beta 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 beta 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 beta 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 beta 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 beta 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.