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LSPM 1459+0857 A and B
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UKIRT Instrumental in Discovery of the First Methane Dwarf Orbiting a Dying Star

The United Kingdom Infrared Telescope (UKIRT) in Hawaii has played a leading role in the discovery of an exotic star system that has revealed new data on the mass and age of some rare and unique stars.
The discovery, made by an international team of astronomers, has provided a new insight into the unusual properties of mysterious methane rich brown dwarfs or T Dwarf stars, of which there are around 200 in our galaxy.
For the first time, scientists are studying a T Dwarf star that is gravitationally linked to a white dwarf star up to one light year away, which enables them to calculate the masses and ages of the two stars for the first time. The T Dwarf star, which has a low mass and low temperature compared to other stars, was identified in the UKIRT Infra-red Deep Sky Survey (UKIDSS) whilst searching for the coolest objects in the Galaxy.

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T dwarf + white dwarf binary
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Astronomers have discovered a unique and exotic star system with a very cool methane-rich (or T-) dwarf star and a 'dying' white dwarf stellar remnant in orbit around each other.
The system is a 'Rosetta Stone' for T-dwarf stars, giving scientists the first good handle on their mass and age.
The team, led by Avril Day-Jones of the Universidad de Chile and including Dr David Pinfield of the University of Hertfordshire as well as astronomers from the University of Montreal, publish their results in the journal Monthly Notices of the Royal Astronomical Society.

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Title: Discovery of a T dwarf + white dwarf binary system
Authors: A.C. Day-Jones, D.J. Pinfield, M.T. Ruiz, H. Beaumont, B. Burningham, J. Gallardo, A. Gianninas, P. Bergeron, R. Napiwotzki, J.S. Jenkins, Z.H. Zhang, D. Murray, S. Catalan, J. Gomes

We present the discovery of the first T dwarf + white dwarf binary system LSPM 1459+0857AB, 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=553545K) and magnetic (B~2MG) hydrogen-rich white dwarf, with an age of at least 4.8Gyrs. The T dwarf is a recent discovery from the UKIRT Infrared Deep Sky Survey (ULAS 1459+0857), and has a spectral type of T4.50.5 and a distance in the range 43-69pc. With an age constraint (inferred from the white dwarf) of >4.8Gyrs we estimate Teff=1200-1500K and logg=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 (16,500-26,500AU, or 365 arcseconds on the sky) is consistent with an evolved version of the more common brown dwarf + main-sequence 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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