A T-Dwarf Binary Candidate

Brown dwarfs are objects that span the gap between the least massive stars and planetary-mass objects. Analysis of observational data from NASA’s Wide-field Infrared Survey Explorer (WISE), together with follow-up observations by ESO’s Very Large Telescope (VLT) in Chile, has led to the discovery of a candidate brown dwarf binary system. Identified as WISE J0612-3036, the binary system consists of a pair of T6 brown dwarfs. T-dwarfs and Y-dwarfs are among the coolest and least luminous brown dwarfs. Assuming WISE J0612-3036 is located ~100 light-years away, the projected separation of the pair of T6 brown dwarfs is about 11 AU.

Figure 1: Artist’s impression of a binary system consisting of two brown dwarfs. Credit: NASA/JPL-Caltech.

Multiplicity is common among stars and it also appears to be common for brown dwarfs. Several T-dwarf binary systems have already been discovered. Most have separations less than 5 AU. The projected separation of about 11 AU makes WISE J0612-3036 an unusually wide system. Another T-dwarf binary system with a similarly large separation is WISEJ1711+3500, whose components are separated by 8 to 15 AU.

If the age of WISE J0612-3036 is ~1 billion years (Gyr), each T6 brown dwarf should have ~30 times the mass of Jupiter and should go around one another with an orbital period ~150 years, assuming a circular orbit. If an older age of ~5 Gyr is assumed, each T6 brown dwarf should have ~60 times the mass of Jupiter and should go around one another with an orbital period ~105 years, again assuming a circular orbit. WISE J0612-3036 is only a candidate brown dwarf binary system because its binarity is based on just a single observation. Additional observations will be needed to confirm if the two T6 brown dwarfs are indeed bound in orbit around one another.

Figure 2: Observations of WISE 0612-3036 clearly showing the two components of the binary system. Huelamo et al. (2015).

Reference:
Huelamo et al. (2015), “WISE J061213.85-303612.5: a new T-dwarf binary candidate”, arXiv:1504.03150 [astro-ph.SR]