Spectral analyses of M, L, and T dwarf stars

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This proposal constitutes a request for support for a three year study of the atmospheres and spectra of cool dwarf stars (ranging from M dwarfs to Brown Dwarfs and Extrasolar Giant Planets [EGPs]) using model atmospheres and synthetic spectra. This project addresses important problems in astrophysics with applications to a wide range of other areas, for example the accurate determination of (sub)stellar parameters and element abundances and the detailed physics of cool stellar atmospheres. The proposed funds will support a student (Matthias Dehn) at the BAT IIa/2 level who will use parts of the results in his PhD thesis. We will carry out detailed non-LTE (NLTE) model atmosphere simulations for cool dwarf stars, brown dwarfs and EGPs using our PHOENIX program package. A fundamental advantage of our approach is that we will use a homogeneous set of model assumptions and input physics for all calculations. As a result of this project we will be able to provide internally consistent model atmospheres and synthetic spectra for nearly all objects in the lower Hertzsprung-Russell diagram. Our models will deliver an improved mapping from observed colors and spectra to stellar masses through the synthetic photometry and evolutionary models.