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Tim Kendall's Extreme Astrophysics

A new T2 dwarf within 15 pc, WISE J2121-6239

28 Sep 2015, 16:03 UTC
A new T2 dwarf within 15 pc, WISE J2121-6239
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Images: NASA/IPAC Infrared Science Archive. These near-infrared (2MASS) images clearly show the object, now identified as WISE J212100.87-623921.6. It was discovered as part of a new study of high proper motion sources from the WISE survey, published today (preprint) and accepted to MNRAS. It is interesting to note that the object is clearly defined in 2MASS with magnitudes J = 15.43, H = 14.54 and K = 14.27, ± 0.05 – 0.07 (2MASS PSC). Both because it is faint – there is no optical counterpart in the SuperCosmos catalogue, preventing a proper motion measurement over a suitably long timeline – and because T dwarfs have quite blue near-infrared colours, it was missed in the previous epoch of surveys. (Moreover, the object is in a region of the sky not observed by the Sloan Digital Sky Survey). Despite the fact that the T dwarfs populate a locus somewhat blueward of the main sequence, there is perhaps more potential for contamination by background stars than in the very red L dwarf locus, as can be seen in the figures below: Above: Example colour selection criteria for ultracool dwarfs in the (J-H)/(H-K) two-colour diagram: blue triangles are nearby main-sequence stars; green points ultracool ...

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