Proper motion of the two parsec distant brown dwarf binary WISE J104915.57-531906AB

luhman-2pc

Image credit: Kevin Luhman/PENN State/Eberly College of Science

The recent discovery of this system, ranking third closest to the Sun after the planet-hosting alpha Centauri system and the red dwarf Barnard’s Star, has not been greeted with as much interest as it merits. Efforts to find the dim red and brown dwarfs close to the Sun over the whole sky including the galactic plane have had some previous successes, notably the record breaking object UGPS 0722-05, which was initially ascribed spectral type T10. The main figure is from the discovery paper and shows the progress of WISE J104915.57-531906 across the sky since being picked up on the DSS-IR plate in 1978. The final frame is the 2010 WISE data. Note that the point spread function of the WISE data is not as narrow as the near-infrared (1999) or red visible (1992) data, as would be expected with imaging in the thermal infrared. With accurate centroiding techniques this does not so much impede astrometric (positional) accuracy. Note also how bright the binary becomes at these increasingly long wavelengths, from the red visible around 8000 Angstroms (0.8 microns) through to WISE wavelengths, 3.6 microns in this case. Above, (lower right panel) significantly higher resolution i-band imaging from the 8 metre Gemini telescope reveals the binary nature of the brown dwarf system itself.

luhman-2pc
Image credit: Kevin Luhman/PENN State/Eberly College of Science
mamajek

The binarity is also apparent in this imaging from 1984 (left). The orientation is the same as for the other images, although the scale is different. The position angle very similar to that shown by the Gemini imaging. This suggests the binary has completed one orbit in the ~ 30 years since, in agreement with the initially published estimate. The primary has spectral type L8 and the secondary is likely near the L/T transition. The separation is 1.5 arcsec, or ~ 3 AU.

Update: Further characterisation of the binary has been performed by Kniazev et al., accepted to ApJ, who find a spectral type of T1.5±2 for the secondary using SALT spectroscopy.

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One Response to “Proper motion of the two parsec distant brown dwarf binary WISE J104915.57-531906AB”

  1. […] Kevin L. Luhman of Pennsylvania State University and discoverer last year of a binary brown dwarf at only 2 parsecs distant, has performed an astrometric search for very nearby companions to the Sun and has ruled out […]

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