Model Atmospheres and Spectra of Zero-Metallicity Brown Dwarfs

Details Model Atmospheres and Spectra of Zero-Metallicity Brown Dwarfs Model Atmospheres and Spectra of Zero-Metallicity Brown Dwarfs

Dec 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...181.2304s&link_type=abstract

American Astronomical Society, 181st AAS Meeting, #23.04; Bulletin of the American Astronomical Society, Vol. 24, p.1158

Astronomy and Astrophysics

Astronomy

Scientific paper

As part of our current effort to compute model atmospheres for brown dwarfs and very low mass stars, we have carefully studied the simpler problem of zero-metallicity atmospheres. These models represent the extreme limit for low-metallicity subdwarfs and the ``primordial'' Population III objects. The models include all significant continuum opacity sources for a mixture of hydrogen and helium and incorporate the most recent determination of the pressure-induced H_2 opacity (Lenzuni et al. 1991) which plays a crucial role in these cool and dense atmospheres. The new P-induced H_2 absorption opacities are up to a factor of 30 larger than the previous estimates. For such stars, the atmosphere always becomes convective at sufficiently large depth. We use the mixing length theory to describe the convective energy transport. We will present synthetic spectra and IR color indices for the relevant parameter range. The emergent flux deviates very strongly from a blackbody distribution and the peculiar pressure dependence of the H_2 absorption leads to bluer spectra for cooler stars. The temperature structure of the atmosphere deviates dramatically from the structure of the corresponding grey atmosphere. This research was supported in part by NSF grant AST-8910780. Lenzuni, P., Chernoff, D. F., and Salpeter, E. E. 1991, Ap. J. Supp., 76, 759.

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