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The DB gap of white dwarfs and semiconvection

Published online by Cambridge University Press:  01 August 2006

Hiromoto Shibahashi
Hiromoto Shibahashi*
Affiliation:
Department of Astronomy, University of Tokyo, Tokyo 113-0033, Japan email: shibahashi@astron.s.u-tokyo.ac.jp
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Abstract

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A remarkable and intriguing fact is that few DB white dwarfs, i.e., objects with a helium-rich atmosphere, are found in the effective temperature range between 45000-30000 K, and this exclusion zone is known as the DB gap. Since the temperatures of the blue and the red edges of the DB gap coincide with the effective temperatures where HeII/III and HeI/II convection zones show up respectively, convective mixing is suspected to be the cause of the appearance of DBs outside the DB gap. Chemical separation due to gravitational settling in the convectively stable atmosphere is then suspected to be the cause of the presence of the DB gap. The white dwarfs which turn back to DBs after the DB gap phase are expected to have a semiconvective layer, which is superadiabatic but convectively stable, when they are located near the red edge of the DB gap. Such white dwarfs are expected to be pulsationally unstable. Discovery of pulsation in them will open up a new class of pulsating white dwarfs to asteroseismic study.

Keywords

Convectiondiffusioninstabilitiesstars: white dwarfsstars: oscillations
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 2 , Symposium S239: Convection in Astrophysics , August 2006 , pp. 274 - 279
Copyright
Copyright © International Astronomical Union 2007

References

Baglin, A. 1971, in: Luyten, W.J. (ed.), White Dwarfs, IAU Symp. 42 (Dordrecht: Reidel), p. 136CrossRefGoogle Scholar
Bergeron, P., Ruiz, M.T. & Leggett, S.K. 1997, ApJS 108, 339CrossRefGoogle Scholar
Fontaine, G. & Michaud, G. 1979, ApJ 231, 826CrossRefGoogle Scholar
Fontaine, G. & Wesemael, F. 1987, in: Philip, A.G.D., Hayes, D.S. & Liebert, J. (eds.), The Second Conference on Faint Blue Stars, IAU Colloq. 95 (Schenectady: Davis), p.319Google Scholar
Fontaine, G. & Wesemael, F. 1997, in: Isern, J.Hernandez, M. & Garxía-Berro, E. (eds.), White Dwarfs, Proc. of the 10th European Workshop on White Dwarfs, Astrophys. and Space Science Library (Dordrecht: Kluwer), vol. 214, p. 173Google Scholar
Hansen, B.M.S. & Liebert, J. 2003, ARAA 41, 465CrossRefGoogle Scholar
Kato, S. 1966, PASJ 18, 374Google Scholar
Ledoux, P. 1947, ApJ 105, 305CrossRefGoogle Scholar
Liebert, J. 1986, in: Hunger, K., Schönberner, D. & Rao, N.K. (eds.), Hydrogen Deficient Stars and Related Objects, IAU Colloq. 87 (Dordrecht: Reidel), p.367CrossRefGoogle Scholar
Liebert, J., Wesemael, F., Hansen, C.J., Fontaine, G., Shipman, H.L., Sion, E.M., Winget, D.E. & Greenm, R.F. 1986, ApJ 309, 241CrossRefGoogle Scholar
Paquette, C., Pelletier, C., Fontaine, G. & Michaud, G. 1986, ApJS 61, 197CrossRefGoogle Scholar
Schatzman, E. 1958, White Dwarfs (Amsterdam: North-Holland)Google Scholar
Shibahashi, H. 2005, in: Alecian, G., Richard, O & Vauclair, S. (eds.), Element Stratification in Stars: 40 Years of Atomic Diffusion, EAS Publ. Ser. (Les Ulis: EDP Science), vol. 17, p.143Google Scholar
Shibahashi, H. & Osaki, Y. 1976, PASJ 28, 199Google Scholar
Sion, E.M. 1984, ApJ 282, 612CrossRefGoogle Scholar
Unno, W., Osaki, Y., Ando, H., Saio, H. & Shibahashi, H. 1989, Nonradial Oscillations of Stars, 2nd edition (Tokyo: Univ. of Tokyo Press)Google Scholar
Veronis, G. 1965, J. Marine Res. 23, 1Google Scholar