Skip to main content
Log in

Eu III oscillator strengths and europium abundances in Ap stars

  • Published:
Astronomy Letters Aims and scope Submit manuscript

Abstract

We present our calculations of the spectrum and oscillator strengths for the 4f7−(4f65d+4f66s) Eu III transitions. The calculations were performed with Cowan's RCN-RCG-RCE codes in the single-configuration approximation. A comparison of computed level lifetimes with experimental data for three levels shows that the scale of theoretical oscillator strengths could be overestimated by a factor of 3. The theoretical oscillator strengths of red Eu III lines are two orders of magnitude smaller than their astrophysical oscillator strengths derived by Ryabchikova et al. (1999) from the condition of ionization balance. The new oscillator strengths were tested by analyzing the Eu abundance using Eu II and Eu III lines in the spectra of hot peculiar stars (α2 CVn is a typical representative) and cool peculiar stars (β CrB is a typical representative). First, we computed non-LTE corrections, which proved to be significant for α2 CVn. We also analyzed the Eu II λ6645.11-Å line as well as ultraviolet and optical Eu III lines. We show that the new oscillator strengths together with the non-LTE corrections allow the contradiction between the Eu abundances derived by Ryabchikova et al. (1999) separately from optical Eu II and Eu III lines in α2 CVn to be resolved. The new Eu abundance, log(Eu/N tot)=−6.5, also faithfully describes the blended near-ultraviolet resonance Eu III lines. Using the new Eu III oscillator strengths to analyze the spectrum of the cool Ap star β CrB, we found a significant deviation of the n(Eu II)/n(Eu III) ratio from its equilibrium value. For a chemically homogeneous model atmosphere, to obtain the observed intensity of the Eu III λ 6666.35-Å line, the Eu abundance must be increased by two orders of magnitude compared to that required to describe the Eu II λ 6645.11-Å line. We discuss the possibility of explaining the observed intensities of Eu II and Eu III lines in the spectrum of β CrB by the presence of an inhomogeneous atmosphere with Eu concentrated in its uppermost layers. In such atmospheres, the role of non-LTE effects becomes dominant.

This is a preview of subscription content, log in via an institution to check access.

Access this article

Price excludes VAT (USA)
Tax calculation will be finalised during checkout.

Instant access to the full article PDF.

Institutional subscriptions

Similar content being viewed by others

References

  1. L. H. Auer and J. Heasley, Astrophys. J. 205, 165 (1976).

    Article  ADS  Google Scholar 

  2. A. A. Boyarchuk, L. S. Lyubimkov, and N. A. Sakhibullin, Astrofizika 22, 339 (1985).

    ADS  Google Scholar 

  3. R. D. Cowan, The Theory of Atomic Structure and Spectra (Univ. of California Press, Berkeley, 1981).

    Google Scholar 

  4. H.-W. Drawin, Z. Phys. 164, 513 (1961).

    Google Scholar 

  5. J. J. Drake, Mon. Not. R. Astron. Soc. 251, 369 (1991).

    ADS  Google Scholar 

  6. V. L. Khokhlova and V. M. Pavlova, Pis'ma Astron. Zh. 10, 377 (1984) [Sov.Astron.Lett. 10, 158 (1984)].

    ADS  Google Scholar 

  7. O. Kochukhov, N. Piskunov, I. Ilyin, S. Ilyina, and I. Tuominen, in Magnetic Fields Across the Hertzprung-Russel Diagram, Ed. by G. Mathys, S. K. Solanki, and T. Wickramasinghe (Santiago, Chile, 2001) (in press).

  8. F. Kupka, N. Piskunov, T. A. Ryabchikova, et al., Astron. Astrophys., Suppl. Ser. 138, 119 (1999).

    Article  ADS  Google Scholar 

  9. W. C. Martin, R. Zalubas, and L. Hagan, Atomic Energy Levels—The Rare-Earth Elements (National Bureau of Standards, Washington, 1978), NSRDSNBS 60.

    Google Scholar 

  10. L. I. Mashonkina, Astron. Zh. 77, 630 (2000) [Astron. Rep. 44, 558 (2000)].

    Google Scholar 

  11. L. I. Mashonkina and T. Gehren, Astron. Astrophys. 364, 249 (2000).

    ADS  Google Scholar 

  12. L. I. Mashonkina, N. A. Sakhibullin, and N. N. Shimanskaya, Astron. Zh. 73, 212 (1996) [Astron. Rep. 40, 187 (1996)].

    Google Scholar 

  13. G. Michaud, Astrophys. J. 160, 641 (1970).

    Article  ADS  Google Scholar 

  14. P. Palmeri, P. Quinet, Y. Fréemat, et al., Astrophys. J., Suppl. Ser. 129, 367 (2000).

    Article  ADS  Google Scholar 

  15. N. E. Piskunov, in Proceedings of the 2nd Workshop on Solar Polarization, Ed. by J. Stenflo and K. N. Nagendra (Kluwer, Dordrecht, 1999), p. 515.

    Google Scholar 

  16. P. Quinet, P. Palmeri, and E. Biéemont, J. Quant. Spectrosc. Radiat. Transf. 62, 625 (1999).

    Article  Google Scholar 

  17. R. A. Roigand and G. Tondello, J. Opt. Soc. Am. 65, 829 (1975).

    ADS  Google Scholar 

  18. H. van Regemorter, Astrophys. J. 136, 906 (1962).

    ADS  Google Scholar 

  19. T. Ryabchikova, N. Piskunov, I. Savanov, et al., Astron. Astrophys. 343, 229 (1999).

    ADS  Google Scholar 

  20. N. A. Sakhibullin, Tr. Kazan. Gor. Astron. Obs. 48, 9 (1983).

    ADS  Google Scholar 

  21. J. Sugar and N. Spector, J. Opt. Soc. Am. 64, 1484 (1974).

    Google Scholar 

  22. G. M. Wahlgren, Contrib. Astron. Obs. Skalnate Pleso 27, 368 (1998).

    ADS  Google Scholar 

  23. J.-F. Wyart, J. Opt. Soc. Am. 68, 197 (1978).

    ADS  Google Scholar 

  24. J.-F. Wyart and C. Bauche-Arnould, Phys. Scr. 22, 583 (1980 ).

    ADS  Google Scholar 

  25. Z. Zhang, Z. S. Li, H. Lundberg, et al., J. Phys. B 33, 521 (2000).

    ADS  Google Scholar 

Download references

Author information

Authors and Affiliations

Authors

Additional information

__________

Translated from Pis'ma v Astronomicheski\(\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\smile}$}}{l} \) Zhurnal, Vol. 28, No. 1, 2002, pp. 41–55.

Original Russian Text Copyright © 2002 by Mashonkina, Ryabtsev, Ryabchikova.

Rights and permissions

Reprints and permissions

About this article

Cite this article

Mashonkina, L.I., Ryabtsev, A.N. & Ryabchikova, T.A. Eu III oscillator strengths and europium abundances in Ap stars. Astron. Lett. 28, 34–48 (2002). https://doi.org/10.1134/1.1434452

Download citation

  • Received:

  • Issue Date:

  • DOI: https://doi.org/10.1134/1.1434452

Key words

Navigation