Discovery of a T dwarf + white dwarf binary system

  1. A. C. Day-Jones1,2,*,
  2. D. J. Pinfield2,
  3. M. T. Ruiz1,
  4. H. Beaumont2,
  5. B. Burningham2,
  6. J. Gallardo1,
  7. A. Gianninas3,
  8. P. Bergeron3,
  9. R. Napiwotzki2,
  10. J. S. Jenkins1,
  11. Z. H. Zhang2,
  12. D. N. Murray2,
  13. S. Catalán2,
  14. J. Gomes2

Article first published online: 25 OCT 2010

DOI: 10.1111/j.1365-2966.2010.17469.x

Issue

Monthly Notices of the Royal Astronomical Society

Monthly Notices of the Royal Astronomical Society

Volume 410, Issue 2, pages 705–716, January 2011

Additional Information

How to Cite

Day-Jones, A. C., Pinfield, D. J., Ruiz, M. T., Beaumont, H., Burningham, B., Gallardo, J., Gianninas, A., Bergeron, P., Napiwotzki, R., Jenkins, J. S., Zhang, Z. H., Murray, D. N., Catalán, S. and Gomes, J. (2011), Discovery of a T dwarf + white dwarf binary system. Monthly Notices of the Royal Astronomical Society, 410: 705–716. doi: 10.1111/j.1365-2966.2010.17469.x

Author Information

  1. 1

    Departamento de Astronomia, Universidad de Chile, Camino del Observatorio 1515, Santiago, Chile

  2. 2

    Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield, Hertfordshire AL10 9AB

  3. 3

    Département de Physique, Université de Montréal, CP 6128, Succursale Centre-Ville, Montreal, Canada

* E-mail: adjones@das.uchile.cl
Based on observations made with ESO telescopes at the La Silla Paranal Observatory under programme 282.C-5069(A).

Publication History

  1. Issue published online: 30 DEC 2010
  2. Article first published online: 25 OCT 2010
  3. Accepted 2010 August 3. Received 2010 August 2; in original form 2010 March 16

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Keywords:

  • binaries: general;
  • brown dwarfs;
  • white dwarfs

ABSTRACT

We present the discovery of the first T dwarf + white dwarf binary system LSPM 1459+0857 AB, confirmed through common proper motion and spectroscopy. The white dwarf is a high proper motion object from the LSPM catalogue that we confirm spectroscopically to be a relatively cool (Teff= 5535 ± 45 K) and magnetic (B∼ 2 MG) hydrogen-rich white dwarf, with an age of at least 4.8 Gyr. The T dwarf is a recent discovery from the UKIRT Infrared Deep Sky Survey (ULAS 1459+0857) and has a spectral type of T4.5 ± 0.5 and a distance in the range 43–69 pc. With an age constraint (inferred from the white dwarf) of >4.8 Gyr, we estimate Teff= 1200–1500 K and log g= 5.4–5.5 for ULAS 1459+0857, making it a benchmark T dwarf with well-constrained surface gravity. We also compare the T dwarf spectra with the latest LYON group atmospheric model predictions, which, despite some shortcomings, are in general agreement with the observed properties of ULAS 1459+0857. The separation of the binary components (16 500–26 500 au or 365 arcsec on the sky) is consistent with an evolved version of the more common brown dwarf + main-sequence (MS) binary systems now known, and although the system has a wide separation, it is shown to be statistically robust as a non-spurious association. The observed colours of the T dwarf show that it is relatively bright in the z band compared to other T dwarfs of similar type, and further investigation is warranted to explore the possibility that this could be a more generic indicator of older T dwarfs. Future observations of this binary system will provide even stronger constraints on the T dwarf properties, and additional systems will combine to give a more comprehensively robust test of the model atmospheres in this temperature regime.

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