Dust in brown dwarfs and extra-solar planets II. Cloud formation for cosmologically evolving abundances

摘要: Context. Substellar objects have extremely long life spans. The cosmological consequence for older are low abundances heavy elements, which in turn results a wide distribution of over metallicity, hence age. Within their cool atmosphere, dust clouds become dominant feature, affecting the opacity and remaining gas phase abundance elements. Aims. We investigate influence stellar metallicity on formation substellar atmospheres cloud structure its feedback atmosphere. This work has implications general questions star early universe. Methods. utilise numerical simulations to solve set moment equations determine quasi-static (Drift). These model nucleation, kinetic growth composite particles, evaporation, gravitational settling as stationary process. Element conservation augment this system by including element replenishment convective overshooting. integration with an atmosphere code (Phoenix) allows determination consistent (T, p ,v conv)-structure (T – local temperature, pressure, vconv velocity), hence, calculate synthetic spectra. Results. Ag rid Drift-Phoenix was calculated range [M/H] ∈ [+0.5, −0.0, −0.5, ..., −6.0], allow systematic study atmospheric structures throughout evolution find even most metal-poor ([M/H] = −6.0) brown dwarfs. Only massive among youngest dwarfs giant planets can resist formation. For very abundances, temperature inversion develops that drastic impact structure. Conclusions. combination metal depletion uncertainty interior makes modelling intricate problem particular old objects. furthermore show dust-togas ratio does not scale linearly object’s given effective temperature. mean grain sizes composition grains change depending [M/H], influences determines radiative heating cooling, well spectral appearance.