Poster Abstracts

Name/Affiliation:  Esther Buenzli (Max-Planck Institute for Astronomy, Heidelberg)

Title:  Spectral variability observations of the very nearby brown dwarf binary Luhman 16AB with HST

Abstract:
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.