Lithium in LP944-20

We present a new estimate of the lithium abundance in the atmosphere of the brown dwarf LP944-20. Our analysis is based on a self-consistent analysis of low-, intermediate- and high-resolution optical and near-infrared spectra. We obtain logN(Li) = 3.25 +/- 0.25 using fits of our synthetic spectra to the LiI resonance line doublet profiles observed with Very Large Telescope/Ultraviolet-Visual Echelle Spectrograph (VLT/UVES) and Anglo-Australian Telescope/Segmented Pupil/Image Reformatting Array of Lenslets (AAT/SPIRAL). This lithium abundance is over two orders of magnitude larger than previous estimates in the literature. In order to obtain good fits of the resonance lines of KI and RbI and better fits to the TiO molecular absorption around the LiI resonance line, we invoke a semi-empirical model atmosphere with the dusty clouds located above the photosphere. The lithium abundance, however, is not changed by the effects of the dusty clouds. We discuss the implications of our estimate of the lithium abundance in LP944-20 for the understanding of the properties of this benchmark brown dwarf.

Based on observations obtained on the European Southern Observatory at Cerro Paranal, Chile, in programs 68.C-0063(A) and 072.C-0110(B), the Anglo-Australian Telescope at Siding Springs Observatory during commissioning observations for SPIRAL (Segmented Pupil/Image Reformatting Array of Lenslets) instrument and the Keck Observatory in Mauna Kea, Hawaii.

E-mail: yp@mao.kiev.ua