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The Oosterhoff Period Effect and the Age of the Galactic Globular Cluster System

Published online by Cambridge University Press:  15 February 2018

Allan Sandage
Allan Sandage*
Affiliation:
The Observatories of the Carnegie Institution of Washington, 813 Santa Barbara Street, Pasadena, CA 91101, USA

Abstract

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The Oosterhoff division of globular clusters into two dichotomous mean period groups is a result of the variation with metallicity of the combined effects of (1) a mean increase in period with decreasing metallicity, and (2) the change of globular cluster horizontal branch (HB) morphology from the M3 to the M13 HB type within the instability strip in the metallicity range of [Fe/H] between -1.7 and -1.9. A new representation of the Oosterhoff period effect showing this property is made from the individual cluster data in Figure 1. The relation between period and metallicity for cluster and for field RR Lyraes at the blue fundamental edge of the instability strip in the HR diagram as read from this figure is

log Pab = -0.122(±0.02)([Fe/H]) - 0.500(±0.01)

using the metallicity scale of Butler.

The high slope coefficient is consistent with the extant models of the HB when they are read at the varing temperature of the fundamental blue edge given by equation (3) of the text. Most of the current literature treats only the constant temperature condition, which is manifestly incorrect. It is this temperature effect that reconciles the observations and the models.

A new calibration of the absolute magnitudes of RR Lyrae stars as a function of metallicity, combined with new oxygen enhanced isochrones for globular clusters (Bergbusch & VandenBerg 1992) reduces the age of the Galactic globular cluster system to 14.1 ± 0.3 Gyr (internal error). The resulting lower age of the universe which, when combined with a Hubble constant near 50 km s-1 Mpc-1 determined from type I supernovae, shows that the cosmological expansion has been decelerated by an amount consistent with the closure density, permitting Ω ∼ 1 now from the timing test.

Type
Variable Stars as Distance Indicators
Information
International Astronomical Union Colloquium , Volume 139: New Perspectives on Stellar Pulsation and Pulsating Variable Stars , 1993 , pp. 3 - 14
Copyright
Copyright © Cambridge University Press 1993

References

Arp, H. C. 1955, AJ, 60, 317 CrossRefGoogle Scholar
Bergbusch, P. A., & VandenBerg, D. A. 1992, ApJS, 81, 163 CrossRefGoogle Scholar
Blanco, V. 1992, AJ, 104, 734 CrossRefGoogle Scholar
Butler, D. 1975, ApJ, 200, 68 CrossRefGoogle Scholar
Castellani, V. 1983, Mem. Soc. Astr. Ital., 54, 141 Google Scholar
Carney, B. W., Storm, J., & Jones, R. V. 1992, ApJ, 386, 663 Google Scholar
Ciardullo, R. B., & Demarque, P. 1977, Trans. Yale Obs., Vol. 33 Google Scholar
Cacciari, C., Clementini, G., Prevot, L., & Buser, R. 1988, A&A, 209, 141 Google Scholar
Cox, A. N. 1987 in IAU Colloq. 95, Second Conference on Faint Blue Stars, ed. Philip, A.G.D., Hayes, D.S., & Liebert, J.W. (Schenectady: Davis), p 161 Google Scholar
Cox, A. N. 1992, private communicationGoogle Scholar
Dorman|B. 1992, ApJS, 81, 221 Google Scholar
Iben, I. 1971, PASP, 83, 697 CrossRefGoogle Scholar
Iglesias, C. A. & Rogers, F. J. 1991, ApJL, 371, 73 Google Scholar
Jones, R. V., Carney, B. W., & Latham, D. W. 1988, ApJ, 332, 206 Google Scholar
Kinman, T. D. 1959, MNRAS, 119, 538 CrossRefGoogle Scholar
Kovacs, G., Buchler, J. R., Marom, A., Iglesias, C. A., & Rogers, F. J., 1992, A&A, 259, L46 Google Scholar
Lee, Y.-W. 1990, PhD thesis, Yale Univ.Google Scholar
Lee, Y.-W. 1993, these proceedings, pp. 285–294.Google Scholar
Lee, Y.-W., Demarque, P., & Zinn, R. 1990, ApJ, 350, 155 CrossRefGoogle Scholar
Liu, T., & Janes, K. A. 1990, ApJ, 354, 273 CrossRefGoogle Scholar
Nikolov, N., Buchantsova, N. & Frolov, M. 1984, Catalog of RR Lyrae Photometric Properties; Astron. Council, USSR Acad Sci., Sofia.Google Scholar
Oosterhoff, P. Th. 1939, Observatory, 62, 104 Google Scholar
Oosterhoff, P. Th. 1944, Bull. Astr. Inst. Netherlands, 10, 55 Google Scholar
Preston, G. W. 1959, ApJ, 130, 507 CrossRefGoogle Scholar
Preston, G. W. 1961, ApJ, 133, 29 Google Scholar
Racine, R., & Harris, W. E. 1992, AJ, 104, 1068 CrossRefGoogle Scholar
Renzini, A. 1983, Mem. Soc. Astr. Ital., 54, 335 Google Scholar
Rogers, F. J., & Iglesias, C. A. 1992, ApJS, 79, 507 CrossRefGoogle Scholar
Saha, A., Freedman, W. L., Hoessel, J. G., & Mossman, A. E. 1992, AJ, 104, 1072 CrossRefGoogle Scholar
Sandage, A. 1961a, ApJ, 333, 355 CrossRefGoogle Scholar
Sandage, A. 1961b, ApJ, 334, 916 Google Scholar
Sandage, A. 1990, ApJ, 350, 603 Google Scholar
Sandage, A. 1993, AJ, submitted (S93)Google Scholar
Sandage, A. & Cacciari, C. 1990, ApJ, 350, 645 Google Scholar
Sandage, A., Sana, A., Tammann, G. A., Panagia, N., & Macchetto, D. 1993, ApJL, in pressGoogle Scholar
Sawyer Hogg, H. 1939, David Dunlop Obs. Pub., 1, No. 4Google Scholar
Sawyer Hogg, H. 1955, ibid, 2, No. 4Google Scholar
Sawyer Hogg, H. 1973, ibid, 3, No. 6Google Scholar
Schneider, D. P., Schmidt, M., & Gunn, J. E. 1991, AJ, 102, 837 Google Scholar
Simon, N. R. & Clement, C. M. 1993, these proceedings, pp. 304–312.Google Scholar
Stetson, P., VandenBerg, D. A., Bolte, M., Hesser, J. E., & Smith, G. H. 1989, AJ, 97, 1360 Google Scholar
Sweigart, A. V., & Gross, P. G., 1976, ApJS, 32, 367 CrossRefGoogle Scholar
Sweigart, A., Renzini, A., & Tornambe, A., 1987, ApJ, 312, 762 Google Scholar
van Albada, T. S., & Baker, N. 1973, ApJ, 185, 477 CrossRefGoogle Scholar
VandenBerg, D. A. 1983, ApJS, 51, 29 CrossRefGoogle Scholar
Weidemann, V. 1990, ARA&A, 28, 103 Google Scholar
Zinn, R. & West, M. J. 1984, ApJS, 55, 45 CrossRefGoogle Scholar