Journal Article

Evolution of DA white dwarfs in the context of a new theory of convection

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 296, issue 1, pages 206-216
Published in print May 1998 | ISSN: 0035-8711
Published online May 1998 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1046/j.1365-8711.1998.01332.x
Evolution of DA white dwarfs in the context of a new theory of convection

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In this study we compute the structure and evolution of carbon–oxygen DA (hydrogen-rich envelope) white dwarf models by means of a detailed and updated evolutionary code. We consider models with masses from 0.5 to 1.0 M⊙ and we vary the hydrogen layer mass in the interval 10−13MH/M≮10−4. In particular, we treat the energy transport by convection within the formalism of the full-spectrum turbulence theory, as given by the Canuto, Goldman & Mazzitelli (CGM) model. We explore the effect of various hydrogen layer masses on both the surface gravity and the hydrogen burning. Convective mixing at low luminosities is also considered.

One of our main interests in this work has been to study the evolution of ZZ Ceti models, with the aim of comparing the CGM and mixing-length theory (MLT) predictions. In this connection, we find that the temperature profile given by the CGM model is markedly different from that of the ML1 and ML2 versions of the MLT. In addition, the evolving outer convection zone behaves differently in both theories.

We have also computed approximate effective temperatures for the theoretical blue edge of the DA instability strip by using thermal time-scale arguments for our evolving DA models. In this context, we found that the CGM theory leads to blue edges that are cooler than the observed ones. However, because the determination of atmospheric parameters of ZZ Ceti stars is dependent on the assumed convection description in model atmosphere calculations, observed blue edges based on model atmospheres computed considering the CGM theory are required in order to perform a self-consistent comparison of our results with observations. Finally, detailed non-adiabatic pulsational computations of ZZ Ceti models considering the CGM convection would be necessary to place the results found in this paper on a firmer basis.

Keywords: convection; stars: evolution; stars: variables: other; white dwarfs

Journal Article.  0 words. 

Subjects: Astronomy and Astrophysics

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