Name/Affiliation: Esther Buenzli (Max-Planck Institute for Astronomy, Heidelberg)
Spectral variability observations of the very nearby brown dwarf binary Luhman 16AB with HST
The recently discovered very nearby (2 pc) brown dwarf binary Luhman 16AB provides an extraordinary opportunity for detailed study of atmospheric conditions at the L/T transition. There, cloud evolution dramatically alters the observed spectra. The B component, an early T dwarf, was found to be highly variable on time scales of about 5 hours, but with rapidly evolving light curves, indicating evolving patchy cloud cover. For the A component, a late L dwarf, tentative variability was found at wavelengths < 1 micron. We have obtained resolved spectral variability observations at sub-percent precision of both components with HST from 1.1 to 1.66 microns, covering 6.5 hours. We find strong variability of the B component at all wavelengths with significant changes after only one rotation period, while we put firm limits on the variability of the A component. We discuss patchy cloud models and compare the characteristics of the spectral variability to that of other variable brown dwarfs.