Cloud Structure of the Nearest Brown Dwarfs II: High-amplitude variability for Luhman 16 A and B in and out of the 0.99 micron FeH feature

摘要: The re-emergence of the 0.99 $\mu$m FeH feature in brown dwarfs early- to mid-T spectral type has been suggested as evidence for cloud disruption where flux from deep, hot regions below Fe deck can emerge. same mechanism could account color changes at L/T transition and photometric variability. We present first observations spectroscopic variability covering feature. observed spatially resolved very nearby dwarf binary WISE J104915.57-531906.1 (Luhman 16AB), a late-L early-T dwarf, with HST/WFC3 G102 grism 0.8-1.15 $\mu$m. find significant all wavelengths both dwarfs, peak-to-valley amplitudes 9.3% Luhman 16B 4.5% 16A. This represents unambiguous detection estimate rotational period between 4.5 5.5 h, similar 16B. Variability components complicates interpretation unresolved observations. probability finding large amplitude any two is less than 10%. Our may suggest that common but yet unknown important occurrence For objects, nearly constant except deep K I 0.84 No variations are seen across lend strong further support height rather holes silicate clouds, cannot fully rule out iron clouds. re-evaluate diagnostic potential tracer patchiness.