Binarity at the L/T brown dwarf transition. Adaptive optics search for companions
Abstract
Context: Current atmospheric models cannot reproduce some of the characteristics of the transition between the L dwarfs with cloudy atmospheres and the T dwarfs with dust-depleted photospheres. It has been proposed that a majority of the L/T transition brown dwarfs could actually be a combinaison of a cloudy L dwarf and a clear T dwarf. Indeed binarity seems to occur more frequently among L/T transition brown dwarfs.
Aims: We aim to refine the statistical significance of the seemingly higher frequency of binaries. Co-eval binaries would also be interesting test-beds for evolutionary models.
Methods: We obtained high-resolution imaging for six mid-L to late-T dwarfs, with photometric distances between 8 and 33 pc, using the adaptive optics systems NACO at the VLT, and the Lick system, both with the Laser Guide Star.
Results: We resolve none of our targets. Combining our data with published results, we obtain a frequency of resolved L/T transition brown dwarfs of 31^+21-15%, compared to 21^+10-7% and 14^+14-7% for mid-L and T dwarfs (90% of confidence level). These fractions do not significantly support, nor contradict, the hypothesis of a larger binary fraction in the L/T transition. None of our targets has companions with effective temperatures as low as 360-1000 K at separations larger than 0farcs5.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- November 2008
- DOI:
- 10.1051/0004-6361:200810605
- arXiv:
- arXiv:0810.0099
- Bibcode:
- 2008A&A...490..763G
- Keywords:
-
- stars: low-mass;
- brown dwarfs;
- stars: atmospheres;
- technique: high angular resolution;
- stars: binaries: general;
- stars: binaries: visual;
- Astrophysics
- E-Print:
- 6 pages, 4 figures, accepted by A&