Hostname: page-component-cd9895bd7-q99xh Total loading time: 0 Render date: 2024-12-26T20:23:05.438Z Has data issue: false hasContentIssue false
  • English
  • Français

Atmospheres and Abundances of Blue Horizontal Branch Stars and Related Objects

Published online by Cambridge University Press:  19 July 2016

U. Heber
U. Heber*
Affiliation:
Institut für Theoretische Physik und Sternwarte der Universität Kiel Olshausenstr. 40, D-2300 Kiel 1 Federal Republic of Germany

Abstract

Core share and HTML view are not available for this content. However, as you have access to this content, a full PDF is available via the ‘Save PDF’ action button.

Spectroscopic analyses of blue horizontal branch stars, subluminous B- and O-stars and PG 1159 stars are reviewed. These classes of stars trace stellar evolution from the horizontal branch towards the white dwarf cooling sequence. The impact of Non-LTE model atmospheres for the analyses of sdO and PG 1159 stars is outlined. The resulting atmospheric parameters and abundances are used to obtain constraints on the evolutionary status of the different classes of stars. The sdB stars form a homogeneous group and can be identified with models of the extended horizontal branch. Abundance anomalies (deficiency of helium and some metals, enrichment of 3He) observed in Horizontal Branch stars and sdB stars do not give hints to the stars' evolutionary history but are caused by atmospheric diffusion. The class of subluminous O stars is much less homogenous and two subclasses can be defined: the “compact” sdO stars probably evolved from the extended horizontal branch and are hence successors of the sdBs, whereas some sdOs of relatively low gravity are in a post-AGB stage of evolution. The third class, the PG 1159 stars, are amongst the hottest stars known with effective temperatures exceeding 100,000 K and are immediate progenitors of the white dwarfs. The abundance pattern is dominated by carbon and helium with a significant admixture of oxygen, whereas hydrogen and nitrogen are trace elements only. As in the case of the (helium rich) sdO stars these abundances indicate that nuclear processed material is exposed at the stellar surface. The origin of the PG 1159 stars as well as of the “low gravity” sdO stars can be explained by the born-again post-AGB star scenario of Iben et al. (1983).

Type
Horizontal Branch Stars and Binaries
Information
Symposium - International Astronomical Union , Volume 145: Evolution of Stars: The Photospheric Abundance Connection , 1991 , pp. 363 - 373
Copyright
Copyright © Kluwer 1991 

References

Auer, L.H., Mihalas, D. 1969: Astrophys. J. 158, 641.Google Scholar
Baschek, B., Norris, J. 1975: Astrophys. J. 199, 694.Google Scholar
Baschek, B., Sargent, A.I. 1976: Astron. Astrophys. 53, 47.Google Scholar
de Boer, K.S., Heber, U., Richtler, T. 1988: Astron. Astrophys. 202, 113.Google Scholar
Caloi, V. 1989: Astron. Astrophys. 221, 27.Google Scholar
Caloi, V. 1990: Astron. Astrophys. 232, 67.Google Scholar
Cannon, R.D. 1981: Proceedings of IAU Symp. No. 105: Observational tests of the stellar evolution theory , eds. Maeder, A. and Renzini, A., Dordrecht: Reidel, p. 123.Google Scholar
Crocker, D.A., Rood, R.T., O'Connell, R.W. 1989: Astrophys. J. 332, 236.Google Scholar
Dreizler, S., Heber, U., Werner, K., Moehler, S., de Boer, K.S. 1990: Astron. Astrophys. 235, 234.Google Scholar
Glaspey, J.W., Michaud, G., Moffat, A.F.J., Demers, S. 1989: Astrophys. J. 339, 926.CrossRefGoogle Scholar
Green, R.F., Liebert, J. 1987: Proceedings of IAU colloquium No. 95: The Second Conference on Faint Blue Stars , eds. Philip, A.G.D., Hayes, D.S. and Liebert, J., Schenectady: Davis Press, p. 261.Google Scholar
Greenstein, J.L., Sargent, A.I. 1974: Astrophys. J. Suppl. 28, 157.Google Scholar
Greggio, L., Renzini, A. 1990: ESO-preprint 697, 1.Google Scholar
Groth, H.G., Kudritzki, R.P., Heber, U. 1985: Astron. Astrophys. 152, 107.Google Scholar
Hartoog, M.R. 1979: Astrophys. J. 231, 161.CrossRefGoogle Scholar
Heber, U. 1986: Astron. Astrophys. 155, 33.Google Scholar
Heber, U. 1987a: Mitt. astron. Ges. 70, 71.Google Scholar
Heber, U. 1987b: Proceedings of IAU colloquium No. 95: The Second Conference on Faint Blue Stars , eds. Philip, A.G.D., Hayes, D.S. and Liebert, J., Schenectady: Davis Press, p. 79.Google Scholar
Heber, U. 1990: Astron. Astrophys. , in preparation.Google Scholar
Heber, U., Hunger, K. 1987: Proceedings of IAU colloquium No. 95: The Second Conference on Faint Blue Stars , eds. Philip, A.G.D., Hayes, D.S. and Liebert, J., Schenectady: Davis Press, p. 599.Google Scholar
Heber, U., Hamann, W.-R., Hunger, K., Kudritzki, R.P., Simon, K.P., Mendez, R.H. 1984: Astron. Astrophys. 136, 331.Google Scholar
Heber, U., Kudritzki, R.P., Caloi, V., Castellani, V., Danziger, J., Gilmozzi, R. 1986: Astron. Astrophys. 162, 171.Google Scholar
Heber, U., Dreizler, S., de Boer, K.S., Moehler, S., Richtler, T. 1988: Astron. Ges. Abs. Ser. 1, 16.Google Scholar
Hunger, K., Gruschinske, J., Kudritzki, R.P., Simon, K.P. 1981: Astron. Astrophys. 95, 204.Google Scholar
Husfeld, D., Butler, K., Heber, U., Drilling, J.S. 1989: Astron. Astrophys. 222, 150.Google Scholar
Iben, I. Jr. 1984: Astrophys. J. 277, 333.Google Scholar
Iben, I. Jr. 1990: Astrophys. J. 353, 215.Google Scholar
Iben, I. Jr., Kaler, J.B., Truran, J.W., Renzini, A. 1983: Astrophys. J. 264, 605.Google Scholar
Iben, I. Jr., Tutukov, A.V. 1985: Astrophys. J. Suppl. 58, 661.CrossRefGoogle Scholar
Iben, I. Jr., Fujimoto, M.Y., Sugimoto, D., Miyaji, S. 1986: Astrophys. J. 304, 217.Google Scholar
Kudritzki, R.P. 1987: Proceedings of IAU colloquium No. 95: The Second Conference on Faint Blue Stars , eds. Philip, A.G.D., Hayes, D.S. and Liebert, J., Schenectady: Davis Press, p. 177.Google Scholar
Lamontagne, R., Wesemael, F., Fontaine, G., Sion, E.M. 1985: Astrophys. J. 299, 496.Google Scholar
Mc Graw, J.T., Starrfield, S., Liebert, J., Green, R.F. 1989: Proc. IAU coll. No. 58: White Dwarfs and Variable Degenerate Stars , eds. van Horn, H.M., Weidemann, V., Rochester, p. 377.Google Scholar
Michaud, G., Bergeron, P., Wesemael, F., Fontaine, G. 1985: Astrophys. J. 299, 741.CrossRefGoogle Scholar
Michaud, G., Bergeron, P., Heber, U., Wesemael, F. 1989: Astrophys. J. 338, 417.Google Scholar
Moehler, S., Heber, U., de Boer, K.S. 1990: Astron. Astrophys. , in press.Google Scholar
Rauch, T., Heber, U., Hunger, K., Werner, K., Neckel, Th. 1990: Astron. Astrophys. , in press.Google Scholar
Sargent, W.L.W., Jugaku, J. 1961: Astrophys. J. 134, 777.Google Scholar
Schönberner, D. 1979: Astron. Astrophys. 79, 108.Google Scholar
Schönberner, D. 1983: Astrophys. J. 272, 708.Google Scholar
Schönberner, D., Drilling, J.S. 1984: Astrophys. J. 278, 702.Google Scholar
Starrfield, S. 1987: Proceedings of IAU colloquium No. 95: The Second Conference on Faint Blue Stars , eds. Philip, A.G.D., Hayes, D.S. and Liebert, J., Schenectady: Davis Press, p. 309.Google Scholar
Vauclair, G., Liebert, J. 1987: in: Exploring the Universe with the IUE Satellite ed. Kondo, Y., Reidel, Dordrecht, 355.Google Scholar
Viton, M., Deleuil, M., Tobin, W., Prevot, L., Bouchet, P. 1990: Astron. Astrophys. , in press.Google Scholar
Werner, K. 1986: Astron. Astrophys. 161, 177.Google Scholar
Werner, K. 1988: Astron. Astrophys. 204, 159.Google Scholar
Werner, K., Husfeld, D. 1985: Astron. Astrophys. 148, 417.Google Scholar
Werner, K., Heber, U., Hunger, K. 1990: Astron. Astrophys. , submitted.Google Scholar