Journal of Astrophysics and Astronomy

, Volume 2, Issue 3, pp 215–244 | Cite as

Mass segregation in globular clusters

  • K. K. Scaria
  • M. K. V. Bappu


Photoelectric aperture-photometry ofω Cen inU, B, V, R andI bands has established that the cluster is bluer between 2 arcmin and 4 arcmin from the centre, than it is elsewhere. The difference inB - I colour between the centre and this blue zone is ≃ 0.45 mag. The core radius is found to be dependant on the wavelength band chosen for observation, the smallest core radius being for theI band. Equidensitometry ofω Cen inB, V and infrared bands shows a wavelength dependence with the cluster being nearly spherical in the infrared band. It shows a maximum ellipticity around 3 arcmin from the cluster centre. The blue contribution in this zone comes from both a diffuse background of unresolved stars and an increase in the relative abundance of horizontal branch (HB) stars. The similarity between the diffuse background and the HB stars has been demonstrated. A photographic subtraction technique is used to study the distribution of HB stars in the cluster.

Results of equidensitometry of the cluster 47 Tuc, obtained in the present study, are compared with the earlier results of photoelectric photometry. Here too an increase in ellipticity is associated with an increase in the blueness of the cluster. All globular clusters studied so far for ellipticity show a similarity in the dependence of the ellipticity on the distance from the centre. The ellipticity has small values near the centre and in the outer regions, with the maximum value in between. We suggest that the red stars in globular clusters have a nearly spherical distribution. The blue stars form a bulge around the core with a more elliptical distribution and a different orientation. A similarity between the ellipticity aspects of both the globular clusters and rotation in the nucleus of M 31 is pointed out; the M 31 nucleus may thus show a bluer colour and smaller UV excess around the region where the rotation curve shows a peak.

Key words

globular clusters ω Centauri photoelectric photometry of globular clusters equidensitometry horizontal branch stars 


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.


  1. Arp, H. C. 1958,Astr. J.,63, 118.CrossRefADSGoogle Scholar
  2. Cathey, L. R. 1974,Astr. J.,79, 1370.CrossRefADSGoogle Scholar
  3. Chun, M. S., Freeman, K. C. 1979,Astrophys. J.,227, 93.CrossRefADSGoogle Scholar
  4. Da Costa, G. S. 1979,Astr. J.,84, 505.CrossRefADSGoogle Scholar
  5. Dickens, R. J., Woolley, R. v.d. R. 1967,R. Obs. Bull, No. 128.Google Scholar
  6. Eggen, O. J., Sandage, A. R. 1965,Astrophys. J.,141, 821.CrossRefADSGoogle Scholar
  7. Fernie, J. D. 1974,Publ. astr. Soc. Pacific,86, 837.CrossRefADSGoogle Scholar
  8. Freeman, K. C., Rodgers, A. W. 1975,Astrophys. J.,201, L71.CrossRefADSGoogle Scholar
  9. Gascoigne, S. C. B., Burr, E. J. 1956,Mon. Not. R. astr. Soc.,116, 570.ADSGoogle Scholar
  10. Geyer, E. H. 1967,Z. Astrophys.,66, 16.ADSGoogle Scholar
  11. Hartwick, F. D. A. 1970,Astrophys. J.,161, 845.CrossRefADSGoogle Scholar
  12. Högner, W., Kadla, Z. I., Richter, N., Strugatskaya, A. A. 1973,Soviet Astr.,16, 843.ADSGoogle Scholar
  13. Illingworth, G., Illingworth, W. 1976,Astrophys. J. Suppl. Ser.,30, 227.CrossRefADSGoogle Scholar
  14. Iriarte, B., Johnson, H. L., Mitchell, R. I., Wisnieswski, W. 1965,Sky Telesc.,30, 21.ADSGoogle Scholar
  15. Johnson, H. L., Sandage, A. R. 1956,Astrophys. J.,124, 379.CrossRefADSGoogle Scholar
  16. Johnson, H. M. 1961,Astrophys. J.,133, 309.CrossRefADSGoogle Scholar
  17. Kadla, Z. I. 1966,Soviet Astr. 10, 97.ADSGoogle Scholar
  18. Kadla, Z. I., Richter, N., Strugatskaya, A. A., Högner, W. 1976,Soviet Astr.,20, 49.ADSGoogle Scholar
  19. King, I. R. 1962,Astr. J.,67, 471.CrossRefADSGoogle Scholar
  20. King, I. R. 1966a,Astr. J.,71, 64.CrossRefADSGoogle Scholar
  21. King, I. R. 1966b,Astr. J.,71, 276.CrossRefADSGoogle Scholar
  22. Light, E. S., Danielson, R. E., Schwarzschild, M. 1974,Astrophys. J.,194, 257.CrossRefADSGoogle Scholar
  23. Lindsay, E. M. 1956,in Vistas in Astronomy, Ed. A. Beer, Pergamon Press, New York, p. 1057.Google Scholar
  24. Martin, W. Chr. 1938,Ann. Sterrew. Leiden, XVII, Part 2.Google Scholar
  25. Norris, J. E. 1980, inGlobular Clusters, Ed. D. Hanes and B. Medore, Cambridge University Press, p. 113.Google Scholar
  26. Norris, J., Bessell, M. S. 1975,Astrophys. J.,201, L76.CrossRefADSGoogle Scholar
  27. Oort, J. H., van Herk, G. 1959,Bull. astr. Inst. Netherl. 14, 299.ADSGoogle Scholar
  28. Peterson, C. J. 1978,Astrophys. J.,221, 80.CrossRefADSGoogle Scholar
  29. Peterson, C. J., King, I. R. 1975,Astr. J.,80, 427.CrossRefADSGoogle Scholar
  30. Poveda, A., Allen, C. 1975,Astrophys. J.,197, 155.CrossRefADSGoogle Scholar
  31. Rusev R. M. 1974,Sov. Astron.,18, 71.ADSGoogle Scholar
  32. Sandage, A. R. 1953,Astr. J.,58, 61.CrossRefADSGoogle Scholar
  33. Sandage, A. 1957,Astrophys. J.,125, 422.CrossRefADSGoogle Scholar
  34. Sandage, A. 1970,Astrophys. J.,162, 841.CrossRefADSGoogle Scholar
  35. Sandage, A., Walker, M. F. 1966,Astrophys. J.,143, 313.CrossRefADSGoogle Scholar
  36. Scaria, K. K. 1980,Kodaikanal Obs. Bull, (in press).Google Scholar
  37. Sistero, R. F., Fourcade, C. R. 1970,Astr. J.,75, p. 34.CrossRefADSGoogle Scholar
  38. Strauss, F. M. 1978,Astr. Astrophys. Suppl. Ser.,33, 315.ADSGoogle Scholar
  39. Strom, S. E., Strom, K. M. 1971,Astr. Astrophys.,14, 111.ADSGoogle Scholar
  40. Strom, S. E., Strom, K. M., Goad, J. W. 1976,Astrophys. J.,204, 684.CrossRefADSGoogle Scholar
  41. Walker, M. F. 1974,Publ. astr. Soc. Pacific,86, 861.CrossRefADSGoogle Scholar

Copyright information

© Indian Academy of Sciences 1981

Authors and Affiliations

  • K. K. Scaria
    • 1
  • M. K. V. Bappu
    • 1
  1. 1.Indian Institute of AstrophysicsBangalore

Personalised recommendations