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δ Scuti and RRs Type Variables: Theoretical Aspects

Published online by Cambridge University Press:  12 April 2016

J. Otzen Petersen
J. Otzen Petersen*
Affiliation:
Copenhagen University Observatory, Øster Voldgade 3, DK-1350 Copenhagen, K Denmark

Abstract

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Theoretical problems in connection with δ Sct and RRs type variables are reviewed. All evidence shows that δ Sct stars are normal main-sequence or early post main-sequence stars. Results of linear stability analyses of δ Sct models agree well with observations, the presence of non-variables in the strip being understandable in terms of helium diffusion. Excitation of non-radial modes may also occur; comparison of observed multiple periodicities with the theoretically derived period patterns for radial and non-radial modes is discussed as a means to distinguish between these possibilities.

It is not known whether RRs variables are of the same nature as δ Sct stars or in a late evolutionary state with low mass. RRs variables pulsate in radial modes, and recent linear stability analyses seem to agree well with observations for both normal and low masses. The reason for the difference in amplitude between RRs and δ Sct stars is not known. Non-linear investigations may provide important information in the near future. The observed period ratios of RRs variables indicate for most of the double mode pulsators a slight deficiency in heavy elements and a normal mass; but more detailed investigations of this problem are needed.

Type
Invited Papers
Information
International Astronomical Union Colloquium , Volume 29: Multiple Periodic Variable Stars , 1976 , pp. 195 - 222
Copyright
Copyright © Reidel 1976

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