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An extremely primitive star in the Galactic halo


The early Universe had a chemical composition consisting of hydrogen, helium and traces of lithium1; almost all other elements were subsequently created in stars and supernovae. The mass fraction of elements more massive than helium, Z, is known as ‘metallicity’. A number of very metal-poor stars has been found2,3, some of which have a low iron abundance but are rich in carbon, nitrogen and oxygen4,5,6. For theoretical reasons7,8 and because of an observed absence of stars with Z < 1.5 × 10−5, it has been suggested that low-mass stars cannot form from the primitive interstellar medium until it has been enriched above a critical value of Z, estimated to lie in the range 1.5 × 10−8 to 1.5 × 10−6 (ref. 8), although competing theories claiming the contrary do exist9. (We use ‘low-mass’ here to mean a stellar mass of less than 0.8 solar masses, the stars that survive to the present day.) Here we report the chemical composition of a star in the Galactic halo with a very low Z (≤ 6.9 × 10−7, which is 4.5 × 10−5 times that of the Sun10) and a chemical pattern typical of classical extremely metal-poor stars2,3—that is, without enrichment of carbon, nitrogen and oxygen. This shows that low-mass stars can be formed at very low metallicity, that is, below the critical value of Z. Lithium is not detected, suggesting a low-metallicity extension of the previously observed trend in lithium depletion11. Such lithium depletion implies that the stellar material must have experienced temperatures above two million kelvin in its history, given that this is necessary to destroy lithium.

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Figure 1: Observed spectra of SDSS J102915+172927.
Figure 2: Lithium abundance of SDSS J102915+172927 compared to that of other metal-poor stars.


  1. Iocco, F., Mangano, G., Miele, G., Pisanti, O. & Serpico, P. D. Primordial nucleosynthesis: from precision cosmology to fundamental physics. Phys. Rep. 472, 1–76 (2009)

    ADS  CAS  Article  Google Scholar 

  2. Cayrel, R. et al. First stars V — Abundance patterns from C to Zn and supernova yields in the early Galaxy. Astron. Astrophys. 416, 1117–1138 (2004)

    ADS  CAS  Article  Google Scholar 

  3. Bonifacio, P. et al. First stars XII. Abundances in extremely metal-poor turnoff stars, and comparison with the giants. Astron. Astrophys. 501, 519–530 (2009)

    ADS  CAS  Article  Google Scholar 

  4. Frebel, A., Collet, R., Eriksson, K., Christlieb, N. & Aoki, W. HE 1327–2326, an unevolved star with [Fe/H]&lt;−5.0. II. New 3D–1D corrected abundances from a Very Large Telescope UVES spectrum. Astrophys. J. 684, 588–602 (2008)

    ADS  CAS  Article  Google Scholar 

  5. Christlieb, N. et al. A stellar relic from the early Milky Way. Nature 419, 904–906 (2002)

    ADS  CAS  Article  Google Scholar 

  6. Norris, J. E. et al. HE 0557–4840: ultra-metal-poor and carbon-rich. Astrophys. J. 670, 774–788 (2007)

    ADS  CAS  Article  Google Scholar 

  7. Bromm, V. & Loeb, A. The formation of the first low-mass stars from gas with low carbon and oxygen abundances. Nature 425, 812–814 (2003)

    ADS  CAS  Article  Google Scholar 

  8. Schneider, R., Ferrara, A., Salvaterra, R., Omukai, K. & Bromm, V. Low-mass relics of early star formation. Nature 422, 869–871 (2003)

    ADS  CAS  Article  Google Scholar 

  9. Nakamura, F. & Umemura, M. On the initial mass function of Population III stars. Astrophys. J. 548, 19–32 (2001)

    ADS  CAS  Article  Google Scholar 

  10. Caffau, E., Ludwig, H.-G., Steffen, M., Freytag, B. & Bonifacio, P. Solar chemical abundances determined with a CO5BOLD 3D model atmosphere. Sol. Phys. 268, 255–269 (2011)

    ADS  CAS  Article  Google Scholar 

  11. Sbordone, L. et al. The metal-poor end of the Spite plateau. I. Stellar parameters, metallicities, and lithium abundances. Astron. Astrophys. 522, A26 (2010)

    Article  Google Scholar 

  12. D'Odorico, S. et al. X-shooter UV- to K-band intermediate-resolution high-efficiency spectrograph for the VLT: status report at the final design review. Proc. SPIE 6269, 626933 (2006)

    Article  Google Scholar 

  13. Dekker, H., D'Odorico, S., Kaufer, A., Delabre, B. & Kotzlowski, H. Design, construction, and performance of UVES, the echelle spectrograph for the UT2 Kueyen Telescope at the ESO Paranal. Proc. SPIE 4008, 534–545 (2000)

    ADS  Article  Google Scholar 

  14. Chieffi, A. & Limongi, M. The explosive yields produced by the first generation of core collapse supernovae and the chemical composition of extremely metal poor stars. Astrophys. J. 577, 281–294 (2002)

    ADS  CAS  Article  Google Scholar 

  15. Andrievsky, S. M. et al. Non-LTE abundances of Mg and K in extremely metal-poor stars and the evolution of [O/Mg], [Na/Mg], [Al/Mg], and [K/Mg] in the Milky Way. Astron. Astrophys. 509, A88 (2010)

    Article  Google Scholar 

  16. Frebel, A., Johnson, J. L. & Bromm, V. Probing the formation of the first low-mass stars with stellar archaeology. Mon. Not. R. Astron. Soc. 380, L40–L44 (2007)

    ADS  Article  Google Scholar 

  17. Spite, M. & Spite, F. Lithium abundance at the formation of the Galaxy. Nature 297, 483–485 (1982)

    ADS  CAS  Article  Google Scholar 

  18. Bonifacio, P. et al. First stars VII — Lithium in extremely metal poor dwarfs. Astron. Astrophys. 462, 851–864 (2007)

    ADS  CAS  Article  Google Scholar 

  19. González Hernández, J. I. et al. First stars XI. Chemical composition of the extremely metal-poor dwarfs in the binary CS 22876–032. Astron. Astrophys. 480, 233–246 (2008)

    ADS  Article  Google Scholar 

  20. Norris, J. E., Ryan, S. G., Beers, T. C. & Deliyannis, C. P. Extremely metal-poor stars. III. The Li-depleted main-sequence turnoff dwarfs. Astrophys. J. 485, 370–379 (1997)

    ADS  CAS  Article  Google Scholar 

  21. Richard, O., Michaud, G. & Richer, J. Implications of WMAP observations on Li abundance and stellar evolution models. Astrophys. J. 619, 538–548 (2005)

    ADS  CAS  Article  Google Scholar 

  22. Jedamzik, K. & Pospelov, M. Big Bang nucleosynthesis and particle dark matter. N. J. Phys. 11, 105028 (2009)

    Article  Google Scholar 

  23. Ryan, S. G., Gregory, S. G., Kolb, U., Beers, T. C. & Kajino, T. Rapid rotation of ultra-Li-depleted halo stars and their association with blue stragglers. Astrophys. J. 571, 501–511 (2002)

    ADS  Article  Google Scholar 

  24. Boesgaard, A. M. Beryllium in ultra-lithium-deficient halo stars: the blue straggler connection. Astrophys. J. 667, 1196–1205 (2007)

    ADS  CAS  Article  Google Scholar 

  25. Abazajian, K. N. et al. The seventh data release of the Sloan Digital Sky Survey. Astrophys. J. 182 (Suppl.). 543–558 (2009)

    Article  Google Scholar 

  26. Ludwig, H.-G. et al. Extremely metal-poor stars from the SDSS. Phys. Scripta T 133, 014037 (2008)

    ADS  Article  Google Scholar 

  27. Kurucz, R. L. ATLAS12, SYNTHE, ATLAS9, WIDTH9, et cetera. Mem. Soc. Astron. Ital. Suppl. 8, 14–24 (2005)

    Google Scholar 

  28. Ludwig, H.-G. et al. The CIFIST 3D model atmosphere grid. Mem. Soc. Astron. Ital. 80, 711–714 (2009)

    ADS  Google Scholar 

  29. François, P. et al. First stars. VIII. Enrichment of the neutron-capture elements in the early Galaxy. Astron. Astrophys. 476, 935–950 (2007)

    ADS  Article  Google Scholar 

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The spectra were secured through X-Shooter Guaranteed Time Observations (GTOs) and ESO Director's Discretionary Time at the ESO VLT Kueyen 8.2-m telescope. E.C. is a Gliese fellow.

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Authors and Affiliations



E.C. developed the code for the analysis of the SDSS spectra, selected the targets for high resolution follow-up, performed the chemical analysis of X-Shooter and UVES spectra and was mainly responsible for writing the paper. P.B. supervised the project and was the Principal Investigator of the ESO proposals. P.F. reduced the X-Shooter data and cross-checked the chemical analysis. L.S. reduced the UVES data. L.M. performed the X-Shooter observations. M.S. and F.S. cross-checked the chemical analysis and contributed to writing the paper. H.-G.L. provided the codes for 3D hydrodynamical simulations and spectral synthesis. R.C. was the main inspirer of this project. S.Z. was responsible for the interpretation of the kinematical data. F.H. and S.R. were respectively the French and Italian Principal Investigators of X-Shooter, who were granted the GTO and decided to invest it in this project. P.M., V.H. and all the other authors contributed to the astrophysical interpretation and to the final version of the paper.

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Correspondence to Elisabetta Caffau.

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The authors declare no competing financial interests.

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Caffau, E., Bonifacio, P., François, P. et al. An extremely primitive star in the Galactic halo. Nature 477, 67–69 (2011).

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