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Journal of Astrophysics and Astronomy

, Volume 12, Issue 2, pp 133–178 | Cite as

MK morphological study of Am stars at 66 Å/mm

  • S. Sreedhar Rao
  • K. D. Abhyankar
Article

Abstract

The pseudo-luminosity effect in the metallic line A-type stars found by Abt & Morgan (1976) is confirmed in a random sample of 27 Am stars. From a morphological study of their spectra in the wavelength interval 3850-4400 Å at a reciprocal dispersion of 66 Å/mm, revised spectral types are given on the MK system for their K-line and metallic-line spectra. This shows that: (a) our segregation of weak Am from the Am stars largely agrees with that by Cowleyet al. (1969); (b) all the stars in the sample are dwarfs according to their K-line classification; (c) more than 80 per cent exhibit the pseudo-luminosity effect significantly, with their metallic-line spectra resembling a giant or even a supergiant in the violet (3850-4100 Å), and a giant rather than a dwarf in the blue region (4260-4400 Å); (d) in two-thirds of the stars under (c), the Sr n 4077 Å line is found to have a markedly brighter luminosity class compared to any region, and in more than one-third of the sample it is comparable to that in Ap stars; (e) at least five stars exhibit characteristics which might suggest a spectrum variability: among these, the most striking example is 41 Sex A which was found to show a phase-modulated spectrum variation hitherto unknown in Am stars; (f) the metallic-line spectra of another five stars appear to be similar to A-shell type in differing degrees; (g) less than 20 per cent of the sample comprises stars which do not show any significant differential luminosity effect; these stars might have been misclassified or perhaps they are in a quiescent state.

We also confirm the conclusion arrived at by Böhm-Vitense & Johnson (1978) that all Am stars may vary and our observations suggest that groups may exist among them.

Key words

stars metallic-line stars, spectrum classification 

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References

  1. Abt, H. A. 1961,Astrophys. J. Suppl.,6, 37.CrossRefADSGoogle Scholar
  2. Abt, H. A. 1965,Astrophys. J. Suppl.,11, 429.CrossRefADSGoogle Scholar
  3. Abt, H. A. 1979,Astrophys. J.,230, 485.CrossRefADSGoogle Scholar
  4. Abt, H. A., Levy, S. G. 1985,Astrophys. J. Suppl.,59, 229.CrossRefADSGoogle Scholar
  5. Abt, H. A., Morgan, W. W. 1976,Astrophys. J.,205, 446.CrossRefADSGoogle Scholar
  6. Abt, H. A., Moyd, K. I. 1973,Astrophys. J.,182, 809.CrossRefADSGoogle Scholar
  7. Batten, A. H. 1961,A. Rev. Astr. Astrophys.,5, 25.CrossRefADSGoogle Scholar
  8. Batten, A. H., Fletcher, J. M., MacCarthy, D. G. 1989,Publ. Dom. Astrophys. Obs.,XVII. Google Scholar
  9. Böhm-Vitense, E. 1960,Z. Astrophys.,49, 243.ADSGoogle Scholar
  10. Böhm-Vitense, E. 1980,Astr. Astrophys.,92, 219.ADSGoogle Scholar
  11. Böhm-Vitense, E., Johnson, P. 1978,Astrophys. J. Suppl.,225, 514.Google Scholar
  12. Borra, E. F., Landstreet, J. D. 1980,Astrophys. J. Suppl.,42, 421.CrossRefADSGoogle Scholar
  13. Burkhart, C. 1979,Astr. Astrophys.,74, 38.ADSGoogle Scholar
  14. Buscombe, W. 1981,MK Spectral Classifications, North-Western Univ., Evanston.Google Scholar
  15. Conti, P. S., Barker, P. K. 1973,Astrophys. J.,186, 185.CrossRefADSGoogle Scholar
  16. Cowley, C. R. 1981,Astrophys. J.,246, 238.CrossRefADSGoogle Scholar
  17. Cowley, A., Cowley, C., Jaschek, M., Jaschek, C. 1969,Astr J.,74, 375.CrossRefADSGoogle Scholar
  18. Cowley, C. R., Henry, R. 1979,Astrophys. J.,233, 633.CrossRefADSGoogle Scholar
  19. Crosswhite, H. M., Dieke, G. H. 1963, inAmerican Institute of Physics Hand Book, McGraw-Hill, New York, p. 7.Google Scholar
  20. Curchod, A., Hauck, B. 1979,Astr. Astrophys. Suppl.,38, 449.ADSGoogle Scholar
  21. Eggen, O. J. 1976,Pub. astr. soc. Pacific,88, 402.CrossRefADSGoogle Scholar
  22. Greenstein, J. L. 1948,Astrophys. J.,107, 151.CrossRefADSGoogle Scholar
  23. Greenstein, J. L. 1949,Astrophys. J.,109, 121.CrossRefADSGoogle Scholar
  24. Guthrie, B. N. G. 1987,Mon. Not. R. astr. Soc.,226, 361.ADSGoogle Scholar
  25. Hauck, B., Curchod, A. 1980,Astr. Astrophys.,92, 289.ADSGoogle Scholar
  26. Hoffleit, D., Jaschek, C. 1982,The Bright Star Catalogue, 4th Rev. Edn, Yale Univ. Obs.Google Scholar
  27. Jaschek, C., Jaschek, M. 1987, inThe Classification of Stars, Cambridge Univ. Press, p. 205.Google Scholar
  28. Jaschek, M., Jaschek, C. 1960,Z. Astrophys.,50, 155.ADSGoogle Scholar
  29. Jaschek, M., Jaschek, C., Andrillant, Y. 1986,Astr. Astrophys. Suppl. Ser.,65, 1.ADSGoogle Scholar
  30. Kitchin, K. R. 1984, inAstrophysical Techniques, Adam & Hilger, Bristol, p. 398.Google Scholar
  31. Kitamura, M., Okazaki, A. 1977,Tokyo astr. Obs. Bull., 2nd Ser., No.246, 2861.Google Scholar
  32. Kitamura, M., Tu-Hwan, K., Kiyokawa, M. 1975,Ann. Tokyo astr. Obs. 2nd Ser., XVI, No. 1.22.Google Scholar
  33. Kurtz, D. W. 1978,Astrophys. J.,221, 869.CrossRefADSGoogle Scholar
  34. Lane, M. C., Lester, J. B. 1980,Astrophys. J.,238, 210.CrossRefADSGoogle Scholar
  35. Lòden, K. 1979, inIAU Coll. 47: Spectral Classification of Future, Eds M. F. McCarthy, A. G. D. Philip & G. V. Coyne, Vatican Obs., p. 31.Google Scholar
  36. Michaud, G. 1970,Astrophys. J.,160, 641.CrossRefADSGoogle Scholar
  37. Michaud, G., Megessier, C., Charland, Y. 1981,Astr. Astrophys.,103, 244.ADSGoogle Scholar
  38. Moore, C. E. 1945, Contr. Princeton Univ. Obs. No. 20.Google Scholar
  39. Morgan, W. W. 1979, inIAU Coll. 47: Spectral Classification of Future, Eds M. F. McCarthy, A. G. D. Philip & G. V. Coyne, Vatican Obs., p. 59.Google Scholar
  40. Morgan, W. W., Abt, H. A., Tapscot, J. W. 1978,Revised MK Spectral Atlas for Stars Earlier than Sun., Yerkes Obs., Univ. Chicago and Kitt Peak National Obs.Google Scholar
  41. Morgan, W. W., Keenan, P. C., Kellman, E. 1943,An Atlas of Stellar Spectra, Univ. Chicago Press.Google Scholar
  42. Roman, G., Morgan, W. W., Eggen, O. J. 1948,Astrophys. J.,107, 107.CrossRefADSGoogle Scholar
  43. Sawyer, M. A., 1963, inExperimental Spectroscopy, Dover, New York, p. 272.Google Scholar
  44. Smith, M. A. 1971,Astr. Astrophys.,11, 325.ADSGoogle Scholar
  45. Sreedhar Rao, S., Abhyankar, K. D., Praveen Nagar, 1990,Astrophys. J.,365, 336.CrossRefADSGoogle Scholar
  46. Titus, J., Morgan, W. W. 1940,Astrophys. J.,92, 257.CrossRefADSGoogle Scholar
  47. Worek, T. F., Zizka, E. R., King, M. W., Beardsley, W. R. 1986,Pub. astr. soc. Pacific,98, 238.CrossRefADSGoogle Scholar
  48. Yamashita, Y., Kyoji, N., Yuji, N. 1977,An Atlas of Representative Stellar Spectra., Univ. Tokyo Press.Google Scholar

Copyright information

© Indian Academy of Sciences 1991

Authors and Affiliations

  • S. Sreedhar Rao
    • 1
  • K. D. Abhyankar
    • 1
  1. 1.Nizamiah and Japal-Rangapur Observatories, Astronomy DepartmentOsmania UniversityHyderabad

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