Kelu 1 - A Brief History

Kelu 1 was the among the first isolated (so called ''free-floating'') brown dwarf identified, and thus served (and still serves) as a proto-typical L-dwarf standard and reference. Not unlike other proto-typical objects (like, e.g, T Tauri, which is the eponym for a whole class of solar-type pre-main sequence stars), Kelu 1 turned out not to proto-typical for its class after all...

Timeline:

• Discovery - based on its large proper motion from 1979 amd 1993, and its (at that time) ''peculiar'' spectral properties, Kelu 1 was identified as a nearby field brown dwarf in 1997 by Ruiz, Leggett and Allard (ApJ 491, L107).
  
• Binary hypothesis - while Ruiz et al. (1997) derived a photometric parallax of 10 pc, Dahm (1999) determined a trigonometric parallax of 19+-1 pc. This let Martin, Delfosse, Basri et al. (1999, AJ 118, 2466) to speculate that Kelu 1 is either extremely young (age less than 0.1 Gyr) or an unresolved binary.
  
• 1st HST companion search - HST/NICMOS observations in August 1998 did not reveal any companion at separations larger than 1.5 A.U. (Martin, Brandner, Basri 1999, Science 283, 1718) (DENIS-P J1228.2-1547, the other object in the sample, was resolved as the first binary brown dwarf).
  
• Companion discovery - Keck adaptive optics observations by Liu & Leggett (2005, ApJ 625, 996) in May 2005, and Gelino, Kulkarni & Stephens (2006, PASP 118, 611) in March and April 2005, indepedently resolved the binary companion to Kelu 1A. HST/NICMOS observation obtained in June 2005, confirmed the physical association of both components, and did reveal clear evidence for orbital motion (Stumpf et al. 2009).
  
• Triple hypothesis - based on astrometric monitoring, Stumpf et al. (2009) derive orbital parameters and a first dynamical mass estimate for the Kelu 1 system. The dynamical mass estimate yields a system mass 50% higher than mass estimates derived from a theoretical evolutionary tracks and the photometric and spectroscopic properties of Kelu 1A and 1B. Thus Stumpf et al. (2009) suggest that either the theoretical models do underestimate the mass (and hence might require revision), or that there is a 3rd, yet unresolved component in the Kelu 1 system. A 3rd component of spectral type T could also explain an unusual spectral feature observed in Kelu 1A.
  

See STScI Press Release "Brown Dwarfs Don't Hang Out With Stars (STScI PR-2009-01) for more details and images.

Movie (2.5 MB) depicting the orbit of Kelu 1B around 1A

Last Update: 8. January 2009