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Structure and Composition of White Dwarf Atmospheres and Convection Zones

Published online by Cambridge University Press:  12 April 2016

K.H. Böhm
K.H. Böhm*
Affiliation:
Astronomy Department, University of Washington

Summary

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We present a brief review of the basic properties of white dwarf atmospheres) convection zones and corona models emphasizing qualitative and intuitive aspects.

1. Atmospheres: We restrict our discussion essentially to very hot and very cool atmospheres since these are especially interesting. With regard to the first type of objects we study the fundamental differences between DA and non-DA models and between their surface fluxes. We discuss the important role of electron scattering in determining the EUV spectra of these objects. The differences between DAs and non-DAs with regard to backwarming effect and surface cooling are summarized.

In our discussion of very cool non-DA atmospheres we emphasize the importance of the additional energy transport mechanisms convection and conduction which should both be very effective for Teff < 4000K and which lead to a very flat temperature gradient. This small gradient must lead to a rather featureless surface flux.

2. Convection Zones. After a survey of the basic numerical results in this field we investigate the question whether convection in white dwarfs has the same basic properties as convection in other stars. We find that contrary to intuitive expectations the Rayleigh number in very cool non-DAs is higher than in the sun (indicating very turbulent convection). The Prandtl number in these objects is 6 to 7 orders of magnitude higher than in the sun.

3. Coronae. The basic methods of the calculation of coronae for white dwarfs are very briefly discussed. We present some results for DA and non-DA stars from unpublished work by D.O. Muchmore and the author. It uses revised values for the emissivities. Only non-DA coronae are of practical interest. DA coronae have much lower densities and temperatures. White dwarf coronae do not generate a stellar wind.

Type
Colloquium Session IV
Information
International Astronomical Union Colloquium , Volume 53: White Dwarfs and Variable Degenerate Stars , August 1979 , pp. 223 - 244
Copyright
Copyright © The University of Rochester 1979

References

Antiochos, S.K. and Underwood, J.H. 1978, Astron. Astrophys.,68, L19.Google Scholar
d’Antona, F. and Mazzitelli, I. 1975, Astron. Astrophys., 44, 253.Google Scholar
d’Antona, F. and Mazzitelli, I. 1979, Astron. Astrophys., 74, 161.Google Scholar
Auer, L.H. and Mihalas, D. 1969, Ap.J., 158, 641.Google Scholar
Auer, L.H. and Mihalas, D. 1970, M.N.R.A.S., 149, 65.Google Scholar
Auer, L.H. and Shipman, H.L. 1977, Ap.J., 211, L103.CrossRefGoogle Scholar
Biermann, L. and Lüst, R. 1960, in Stellar Atmospheres, Ed. Greenstein, J.L., University of Chicago Press, p.260.Google Scholar
Böhm, K.H. 1963, Ap.J., 138, 297.Google Scholar
Böhm, K.H. 1968, Astrophys. Space Sci., 2, 375.Google Scholar
Böhm, K.H. 1969, Astron. Astrophys. 1, 180.Google Scholar
Böhm, K.H. 1970, Ap.J., 162, 919.Google Scholar
Böhm, K.H. 1976, Paper presented at the 2nd European Workshop on White Dwarfs, Monte Porzio, Italy.Google Scholar
Böhm, K.H., Carson, T.R., Fontaine, G. and Van Horn, H.M. 1977, Ap.J., 217, 521.CrossRefGoogle Scholar
Böhm, K.H. and Cassinelli, J. 1971a, Astron. Astrophys., 12, 21.Google Scholar
Böhm, K.H. and Cassinelli, J. 1971b, in Dwarfs, White, Proc. I.A.U. Symp. No. 42, ed. Luyten, W.J., Reidel Publ. Co., p. 130.Google Scholar
Böhm, K.H. and Deinzer, W. 1966, Z.f.A., 63, 177.Google Scholar
Böhm, K.H. and Grenfell, T.C. 1972, Astron. Astrophys. 20, 293.Google Scholar
Böhm, K.H. and Kapranidis, S. 1979, to be submitted to Astron. Astrophys.Google Scholar
Bues, I. 1970, Astron. Astrophys., 7, 91.Google Scholar
Bues, I. 1973, Astron. Astrophys., 28, 181.Google Scholar
Cash, W., Bowyer, S. and Lampton, M. 1978, Ap.J., 221, L87.CrossRefGoogle Scholar
De Loore, C. 1970, Ap. and Space Sci., 6, 60.Google Scholar
Fontaine, G. 1973, Outer Layers of White Dwarf Stars, Ph.D. Thesis. Univ. of Rochester.Google Scholar
Fontaine, G. and Van Horn, H.M. 1976, Ap.J. Suppl., 31, 476.Google Scholar
Fontaine, G., Van Horn, H.M., B8hm, K.H. and Grenfell, T.C. 1974, Ap.J., 193, 205.Google Scholar
Fontaine, G. and Michaud, G. 1979, Diffusion Time Scales in White Dwarfs, Preprint.Google Scholar
Greenstein, J.L. 1969, Comments Astrophys. Space Phys., 1, 62.Google Scholar
Grenfell, T.C. 1974, Astron. Astrophys., 40, 355.Google Scholar
Hearn, A.G. 1975, Astron. Astrophys. 40, 355.Google Scholar
Huppert, H.E. 1977, in Problems of Stellar Convection, ed. Spiegel, E.A. and Zahn, J.P., Springer-Verlag, Heidelberg-New York, p.239.Google Scholar
Koester, D. 1972, Astron. Astrophys. 16, 459.Google Scholar
Koester, D. 1976, Astron. Astrophys., 52, 415.Google Scholar
Koester, D., Liebert, J. and Hege, E.K. 1979, Astron. Astrophys., 71, 163.Google Scholar
Koester, D., Schulz, H. and Weidemann, V. 1979, Astron. Astrophys. (in press).Google Scholar
Kuperus, M. 1965, The Transfer of Mechanical Energy in the Sun and the Heating of the Corona, Reidel Publ. Co., Dordrecht.Google Scholar
Liebert, J. 1977, Astron. Astrophys., 60, 101 Google Scholar
Liebert, J., Dahn, C.C., Gresham, M. and Strittmatter, P.A. 1979, Preprint.Google Scholar
Lighthill, M.J. 1955, in Gas Dynamics of Cosmic Clouds, eds. Burgers, J.M. and van der Hulst, H.C., Interscience Publ., New York, p.429.Google Scholar
Muchmore, D.O. and Böhm, K.H. 1977, Astron. Astrophys., 54, 499. and 57, 473.Google Scholar
Muchmore, D.O. and Böhm, K.H. 1978, Astron. Astrophys., 69, 113.Google Scholar
Mullan, D.J. 1976, Ap.J., 209. 171.Google Scholar
Schatzman, E. 1958, White Dwarfs, North-Holland Publ. Co., Amsterdam.Google Scholar
Shaviv, G. and Salpeter, E. 1973, Ap.J., 184, 191 Google Scholar
Shipman, H.L. 1976, Ap.J., 206, L67.Google Scholar
Strittmatter, P.A. and Wickramasinghe, D.T. 1970, M.N.R.A.S., 150, 435.Google Scholar
Strittmatter, P.A. and Wickramasinghe, D.T. 1971, M.N.R.A.S., 152, 47.Google Scholar
Terashita, Y., Matsushima, S. 1969, Ap.J., 156, 203.Google Scholar
Ulmschneider, P. 1967, Z. f. Ap., 67, 193.Google Scholar
Unno, W. 1963, P.A.S.J., 15, 400.Google Scholar
Van Horn, H.M. 1970, Ap.J., 160, L53.Google Scholar
Vauclair, G. and Fontaine, G. 1979, Ap.J. (in press).Google Scholar
Wegner, G. 1972, Ap.J., 172, 451.Google Scholar
Wehrse, R. 1971, Astron. Astrophys., 19, 453.Google Scholar
Wehrse, R. 1974, Astron. Astrophys., 39, 169.Google Scholar
Wehrse, R. 1976a, Mem. d. Soc. Astron. Italiana, 48, 13.Google Scholar
Wehrse, R. 1976b, Astron. Astrophys., 41, 482.Google Scholar
Wehrse, R. and Liebert, J. 1979, to be publ, in Astron. Astrophys.Google Scholar
Weidemann, V. 1960, Ap.J., 131, 638.Google Scholar
Weidemann, V. 1963, Z. f. Ap., 57, 87.Google Scholar
Weidemann, V. and Koester, D. 1979, Astron. Astrophys. (in press).Google Scholar
Wesemael, F. 1978, Astron. Astrophys., 65, 301.Google Scholar
Wesemael, F. 1979, in preparation.Google Scholar