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Non-Linear Radial Pulsation Models for the Early-Type Helium Stars V652 Her and BX Cir

Published online by Cambridge University Press:  12 April 2016

P. Montañés Rodríguez  and
C.S. Jeffery
P. Montañés Rodríguez
Affiliation:
Armagh Observatory, Armagh, Northern Ireland, UK
C.S. Jeffery
Affiliation:
Armagh Observatory, Armagh, Northern Ireland, UK

Abstract

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Hydrogen-deficient early-type stars have an extremely high surface helium abundance (> 98% by number) and have represented a considerable challenge to stellar evolution theory. Recent work supports the view that they are the product of a merger between two white dwarfs.

All very luminous stars (log L/M > 4) are believed to pulsate, but at effective temperatures around 20 000 K, helium stars with lower luminosities (log-L/M < 3) are also known to pulsate due to iron-group bump instability. The two known cases are V652 Her and BX Cir. Their observed periods are in good agreement with linear theory. Recently high-resolution Spectroscopic observations were used to measure the stellar dimensions and radial velocity curves with high precision.

A hydrodynamic code including recent OPAL opacity data has been used to construct non-linear models of the pulsations of these two stars. The results impose additional constraints on those stellar dimensions, including mass, which remain poorly determined by observation.

Type
Part 3. Nonlinear Effects in Pulsating Stars
Information
International Astronomical Union Colloquium , Volume 185: Radial and Nonradial Pulsations as Probes of Stellar Physics , 2002 , pp. 438 - 441
Copyright
Copyright © Astronomical Society of the Pacific 2002

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