Abstract
The asymptotic giant branch (AGB) phase is the final stage of nuclear burning for low-mass stars. Although Milky Way globular clusters are now known to harbour (at least) two generations of stars1,2, they still provide relatively homogeneous samples of stars that are used to constrain stellar evolution theory3,4,5. It is predicted by stellar models that the majority of cluster stars with masses around the current turn-off mass (that is, the mass of the stars that are currently leaving the main sequence phase) will evolve through the AGB phase6,7. Here we report that all of the second-generation stars in the globular cluster NGC 6752—70 per cent of the cluster population—fail to reach the AGB phase. Through spectroscopic abundance measurements, we found that every AGB star in our sample has a low sodium abundance, indicating that they are exclusively first-generation stars. This implies that many clusters cannot reliably be used for star counts to test stellar evolution timescales if the AGB population is included. We have no clear explanation for this observation.
This is a preview of subscription content, access via your institution
Access options
Subscribe to this journal
Receive 51 print issues and online access
$199.00 per year
only $3.90 per issue
Buy this article
- Purchase on Springer Link
- Instant access to full article PDF
Prices may be subject to local taxes which are calculated during checkout
Similar content being viewed by others
References
Carretta, E., Bragaglia, A., Gratton, R. & Lucatello, S. Na-O anticorrelation and HB. VIII. Proton-capture elements and metallicities in 17 globular clusters from UVES spectra. Astron. Astrophys. 505, 139–155 (2009)
Gratton, R. G., Carretta, E. & Bragaglia, A. Multiple populations in globular clusters. Lessons learned from the Milky Way globular clusters. Astron. Astrophys. Rev. 20, 50 (2012)
Iben, I. & Rood, R. T. Ratio of horizontal branch stars to red giant stars in globular clusters. Nature 224, 1006–1008 (1969)
Buonanno, R., Corsi, C. E. & Fusi Pecci, F. The giant, asymptotic, and horizontal branches of globular clusters. II — Photographic photometry of the metal-poor clusters M15, M92, and NGC 5466. Astron. Astrophys. 145, 97–117 (1985)
Renzini, A. & Fusi Pecci, F. Tests of evolutionary sequences using color-magnitude diagrams of globular clusters. Annu. Rev. Astron. Astrophys. 26, 199–244 (1988)
Kippenhahn, R. & Weigert, A. Stellar Structure and Evolution (Springer, 1990)
Landsman, W. B. et al. Ultraviolet imagery of NGC 6752: a test of extreme horizontal branch models. Astrophys. J. 472, L93–L96 (1996)
Carretta, E., Bragaglia, A., Gratton, R. G., Lucatello, S. & Momany, Y. Na-O anticorrelation and horizontal branches. II. The Na-O anticorrelation in the globular cluster NGC 6752. Astron. Astrophys. 464, 927–937 (2007)
Norris, J., Cottrell, P. L., Freeman, K. C. & Da Costa, G. S. The abundance spread in the giants of NGC 6752. Astrophys. J. 244, 205–220 (1981)
Campbell, S. W. et al. The case of the disappearing CN-strong AGB stars in Galactic globular clusters — preliminary results. Mem. Soc. Astron. Ital. 81, 1004 (2010)
Yong, D., Grundahl, F., Johnson, J. A. & Asplund, M. Nitrogen abundances in giant stars of the globular cluster NGC 6752. Astrophys. J. 684, 1159–1169 (2008)
Smith, G. H. & Tout, C. A. The production of surface carbon depletions among globular cluster giants by interior mixing. Mon. Not. R. Astron. Soc. 256, 449–456 (1992)
Boothroyd, A. I., Sackmann, I.-J. & Ahern, S. C. Prevention of high-luminosity carbon stars by hot bottom burning. Astrophys. J. 416, 762–768 (1993)
Sandquist, E. L. & Bolte, M. Exploring the upper red giant and asymptotic giant branches: the globular cluster M5. Astrophys. J. 611, 323–337 (2004)
Cassisi, S., Salaris, M. & Irwin, A. W. The initial helium content of galactic globular cluster stars from the R-parameter: comparison with the cosmic microwave background constraint. Astrophys. J. 588, 862–870 (2003)
Cassisi, S. & Castellani, V. Degl’Innocenti, S. Piotto, G. & Salaris, M. asymptotic giant branch predictions: theoretical uncertainties. Astron. Astrophys. 366, 578–584 (2001)
Villanova, S., Piotto, G. & Gratton, R. G. The helium content of globular clusters: light element abundance correlations and HB morphology. I. NGC 6752. Astron. Astrophys. 499, 755–763 (2009)
Grundahl, F., Catelan, M., Landsman, W. B., Stetson, P. B. & Andersen, M. I. Hot horizontal-branch stars: the ubiquitous nature of the “jump” in Strömgren u, low gravities, and the role of radiative levitation of metals. Astrophys. J. 524, 242–261 (1999)
Momany, Y. et al. A new feature along the extended blue horizontal branch of NGC 6752. Astrophys. J. 576, L65–L68 (2002)
Sneden, C. A. Carbon and Nitrogen Abundances in Metal-Poor Stars. Ph.D. thesis, Univ. Texas at Austin. (1973)
Kurucz, R. ATLAS9 Stellar Atmosphere Programs and 2 km/s grid. (CD-ROM no. 13, Smithsonian Astrophysical Observatory, 1993)
Alonso, A., Arribas, S. & Martínez-Roger, C. The effective temperature scale of giant stars (F0–K5). II. Empirical calibration of Teff versus colours and [Fe/H]. Astron. Astrophys. 140, 261–277 (1999)
Gratton, R. G., Carretta, E. & Castelli, F. Abundances of light elements in metal-poor stars. I. Atmospheric parameters and a new Teff scale. Astron. Astrophys. 314, 191–203 (1996)
Gratton, R. G., Carretta, E., Eriksson, K. & Gustafsson, B. Abundances of light elements in metal-poor stars. II. Non-LTE abundance corrections. Astron. Astrophys. 350, 955–969 (1999)
Campbell, S. W. & Lattanzio, J. C. Evolution and nucleosynthesis of extremely metal-poor and metal-free low- and intermediate-mass stars. I. Stellar yield tables and the CEMPs. Astron. Astrophys. 490, 769–776 (2008)
Marigo, P. & Aringer, B. Low-temperature gas opacity. ÆSOPUS: a versatile and quick computational tool. Astron. Astrophys. 508, 1539–1569 (2009)
Reimers, D. Circumstellar absorption lines and mass loss from red giants. Mem. Soc. R. Sci. Liege 8, 369–382 (1975)
Clem, J. L., VandenBerg, D. A., Grundahl, F. & Bell, R. A. Empirically constrained color-temperature relations. II. uvby. Astron. J. 127, 1227–1256 (2004)
Acknowledgements
We thank Y. Momany of the European Southern Observatory (ESO, Chile) for providing his UBV photometric data set, which is mentioned in Supplementary Information section 2. S.W.C. acknowledges support from the Australian Research Council’s Discovery Projects funding scheme (project DP1095368). R.J.S. is the recipient of a Sofja Kovalevskaja Award from the Alexander von Humboldt Foundation. F.G. acknowledges funding for the Stellar Astrophysics Centre provided by The Danish National Research Foundation. The research was supported by the ASTERISK project funded by the European Research Council (grant agreement no. 267864). This work was based on observations made with ESO telescopes at the La Silla Paranal Observatory under programme ID 089.D-0038 (principal investigator S.W.C.) and made extensive use of the SIMBAD, Vizier, 2MASS and NASA ADS databases.
Author information
Authors and Affiliations
Contributions
S.W.C. designed and prepared the ESO Very Large Telescope (VLT) observing proposal, collected the spectroscopic data, and prepared the paper. V.D. reduced and analysed the spectroscopic data, and prepared the paper. D.Y. designed and prepared the ESO/VLT observing proposal and assisted in the paper preparation. T.N.C. calculated the stellar models and prepared figures for the paper. J.C.L. assisted in the preparation of the observing proposal and with the paper preparation. R.J.S., G.C.A. and E.C.W. assisted in the paper preparation and made preliminary observations with the Anglo-Australian Telescope. F.G. provided the uvby photometric data for the AGB and red giant branch sample and assisted in the paper preparation.
Corresponding author
Ethics declarations
Competing interests
The authors declare no competing financial interests.
Supplementary information
Supplementary Information
This file contains Supplementary Table 1, Supplementary Discussion and Supplementary References. (PDF 184 kb)
Rights and permissions
About this article
Cite this article
Campbell, S., D’Orazi, V., Yong, D. et al. Sodium content as a predictor of the advanced evolution of globular cluster stars. Nature 498, 198–200 (2013). https://doi.org/10.1038/nature12191
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1038/nature12191
This article is cited by
-
What is a globular cluster? An observational perspective
The Astronomy and Astrophysics Review (2019)
Comments
By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.