An Approach for Retrieving Temperatures and Abundances in Brown Dwarf Atmospheres

摘要

Brown dwarf spectra contain a wealth of information about their molecularabundances, temperature structure, and gravity. We present a new data drivenretrieval approach, previously used in planetary atmosphere studies, to extractthe molecular abundances and temperature structure from brown dwarf spectra.The feasibility of the approach is first demonstrated on a synthetic browndwarf spectrum. Given typical spectral resolutions, wavelength coverage, andnoise properties precisions of tens of percent can be obtained for themolecular abundances and 10s-100s K on the temperature profile. The techniqueis then applied to the well studied brown dwarf, Gl 570D. From this spectralretrieval the spectroscopic radius is constrained to be 0.75 - 0.83$R_{\mathrm{J}}$, $\log(g)$ to be 5.13 - 5.46 and $T_{\mathrm{eff}}$ to bebetween 804 and 849 K. Estimates for the range of abundances and allowedtemperature profiles are also derived. The results from our retrieval approachare in agreement with the self-consistent grid modeling results of Saumon et al(2006). This new approach will allow us to address issues of compositionaldifferences between brown dwarfs and possibly their formation environments,disequilibrium chemistry, missing physics in current grid modeling approachesas well as a many other issues.