Lithium in LP 944-20

Abstract

We present a new estimate of the lithium abundance in the atmosphere of the brown dwarf LP 944-20. Our analysis is based on a self-consistent analysis of low, intermediate and high resolution optical and near-infrared spectra. We obtain log N(Li) = 3.25 +/-0.25 using fits of our synthetic spectra to the Li I resonance line doublet profiles observed with VLT/UVES and 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 K I and Rb I and better fits to the TiO molecular absorption around the Li I 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 LP 944-20 for the understanding of the properties of this benchmark brown dwarf.

14 pages, 17 figs, accepted by MNRAS (upgraded version)

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