Dust in brown dwarfs and extra-solar planets. IV. Assessing TiO2 and SiO nucleation for cloud formation modelling
| العنوان: | Dust in brown dwarfs and extra-solar planets. IV. Assessing TiO2 and SiO nucleation for cloud formation modelling |
|---|---|
| المؤلفون: | Stefan T. Bromley, H. Giles, Christiane Helling, Graham K. H. Lee |
| المساهمون: | University of St Andrews. School of Physics and Astronomy |
| سنة النشر: | 2014 |
| مصطلحات موضوعية: | low-mass, brown dwarfs [Stars], Astrochemistry, Nucleation, Brown dwarf, Methods - numerical, NDAS, FOS: Physical sciences, Context (language use), Astrophysics, AGB [Stars], Planet, Cluster (physics), Astrophysics::Solar and Stellar Astrophysics, QB Astronomy, Physics - Atomic and Molecular Clusters, atmospheres [Stars], Solar and Stellar Astrophysics (astro-ph.SR), Astrophysics::Galaxy Astrophysics, QC, QB, Physics, Earth and Planetary Astrophysics (astro-ph.EP), Number density, Condensation, Astronomy and Astrophysics, Computational Physics (physics.comp-ph), Physics - Atmospheric and Oceanic Physics, QC Physics, Astrophysics - Solar and Stellar Astrophysics, Space and Planetary Science, Atmospheric and Oceanic Physics (physics.ao-ph), Atomic and Molecular Clusters (physics.atm-clus), Physics - Computational Physics, Astrophysics - Earth and Planetary Astrophysics |
| الوصف: | Clouds form in atmospheres of brown dwarfs and planets. The cloud particle formation processes are similar to the dust formation process studied in circumstellar shells of AGB stars and in Supernovae. Cloud formation modelling in substellar objects requires gravitational settling and element replenishment in addition to element depletion. All processes depend on the local conditions, and a simultaneous treatment is required. We apply new material data in order to assess our cloud formation model results regarding the treatment of the formation of condensation seeds. We re-address the question of the primary nucleation species in view of new (TiO2)_N-cluster data and new SiO vapour pressure data. We apply the density functional theory using the computational chemistry package Gaussian 09 to derive updated thermodynamical data for (TiO2)_N-clusters as input for our TiO2 seed formation model. We test different nucleation treatments and their effect on the overall cloud structure by solving a system of dust moment equations and element conservation or a pre-scribed Drift-Phoenix atmosphere structure. Updated Gibbs free energies for the (TiO2)_N-clusters are presented, and a slightly temperature dependent surface tension for T=500 ... 2000K with an average value of sigma_infty = 480.6 erg 1/cm2. The TiO2-seed formation rate changes only slightly with the updated cluster data. A considerably larger effect on the rate of seed formation, and hence on grain size and dust number density, results from a switch to SiO-nucleation. Despite the higher abundance of SiO over TiO2 in the gas phase, TiO2 remains considerably more efficient in forming condensation seeds by homogeneous nucleation followed by heterogeneous grain growth. The paper discussed the effect on the cloud structure in more detail. accepted for publication in A&A (abstract abridged) |
| وصف الملف: | application/pdf |
| اللغة: | English |
| URL الوصول: | https://explore.openaire.eu/search/publication?articleId=doi_dedup___::3eea4acd7d181f1dae8650b807fe72be https://hdl.handle.net/10023/5773 |
| Rights: | OPEN |
| رقم الانضمام: | edsair.doi.dedup.....3eea4acd7d181f1dae8650b807fe72be |
| قاعدة البيانات: | OpenAIRE |
| الوصف غير متاح. |