Evidence of Orbital Motion in the Binary Brown Dwarf Kelu‐1AB

We have resolved Kelu-1 into a binary system with a separation of ~290 masusing the Laser Guide Star Adaptive Optics system on the Keck II telescope. Wehave also re-analyzed a 1998 HST observation of Kelu-1 and find that theobserved PSF is best fit by a binary object separated by 45 mas. Observationson multiple epochs confirm the two objects share a common proper motion andclearly demonstrate the first evidence of orbital motion. Kelu-1B is fainterthan Kelu-1A by 0.39+/-0.01 magnitudes in the K' filter and 0.50+/-0.01magnitudes in the H filter. We derive spectral types of L2+/-1 and L3.5+/-1 forKelu-1A and B, respectively. The separation of flux into the two componentsrectifies Kelu-1's over-luminosity problem that has been known for quite sometime. Given the available data we are able to constrain the inclination of thesystem to >81 degrees and the orbital period to >~40 years.Comment: 15 pages, 3 figures, Accepted to PASP. Changes include: title, author list, new data, more analysis, and new journa