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Infrared spectrum of an extremely cool white-dwarf star

Nature volume 403, pages 57–59 (2000)Cite this article

Abstract

White dwarfs are the remnant cores of stars that initially had masses of less than 8 solar masses. They cool gradually over billions of years, and have been suggested1,2 to make up much of the ‘dark matter’ in the halo of the Milky Way. But extremely cool white dwarfs have proved difficult to detect, owing to both their faintness and their anticipated similarity in colour to other classes of dwarf stars. Recent improved models3,4,5 indicate that white dwarfs are much more blue than previously supposed, suggesting that the earlier searches may have been looking for the wrong kinds of objects. Here we report an infrared spectrum of an extremely cool white dwarf that is consistent with the new models. We determine the star's temperature to be 3,500 ± 200 K, making it the coolest known white dwarf. The kinematics of this star indicate that it is in the halo of the Milky Way, and the density of such objects implied by the serendipitous discovery of this star is consistent with white dwarfs dominating the dark matter in the halo.

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Figure 1: Spectrum of the cool white dwarf WD0346+246.

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Acknowledgements

The UK Infrared Telescope is operated by the Joint Astronomy Centre on behalf of the UK Particle Physics and Astronomy Research Council. Some of the data presented here were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and NASA. The Observatory was made possible by the support of the W. M. Keck Foundation. S.T.H. and S.J.S. were supported by the PPARC; B.R.O. was supported by FUTDI and a Hubble postdoctoral research fellowship.

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Authors and Affiliations

  1. Department of Physics and Astronomy, University of Leicester, University Road, Leicester, LE1 7RH, UK

    S. T. Hodgkin & R. F. Jameson

  2. Department of Astronomy, University of California-Berkeley, 601 Campbell Hall, Berkeley, 94720, California, USA

    B. R. Oppenheimer

  3. Institute for Astronomy, University of Edinburgh, Blackford Hill, Edinburgh, EH9 3HJ, UK

    N. C. Hambly

  4. Isaac Newton Group of Telescopes, Apartado de Correos 321, Santa Cruz de La Palma, La Palma, 38770, Islas Canarias, Spain

    S. J. Smartt

  5. Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Egerton Wharf, Birkenhead, L41 1LD, UK

    I. A. Steele

  6. Institute of Astronomy, Cambridge University, Madingley Road, Cambridge, CB3 0HA, UK

    S. T. Hodgkin & S. J. Smartt

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  1. S. T. Hodgkin
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Correspondence to S. T. Hodgkin.

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Hodgkin, S., Oppenheimer, B., Hambly, N. et al. Infrared spectrum of an extremely cool white-dwarf star. Nature 403, 57–59 (2000). https://doi.org/10.1038/47431

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