arXiv 1801.084822018-01-25astro-ph.EPastro-ph.SR

棕矮星和太阳系外行星VI中的尘埃。评估棕矮星和系外行星体系中的种子形成

Dust in brown dwarfs and extra-solar planets VI. Assessing seed formation across the brown dwarf and exoplanet regimes

Elspeth K. H. Lee, Jasmina Blecic, Christiane Helling

备注：: 23 pages, 16 figures
发表信息：: A&A 614, A126 (2018)
DOI：: 10.1051/0004-6361/201731977

摘要：

云的形成过程开始于种子粒子的形成，之后，表面化学反应生长或侵蚀云粒子。我们调查哪些材料可能会形成云凝结种子的气体温度和压力制度（T $_{\rm gas}$ = 100-2000 K，p $_{\rm gas}$ = 10 $^{-8}$ -100 bar）预计发生在行星和褐矮星大气。我们应用修改后的经典成核理论，需要表面张力和蒸汽压数据的每个固体物种，这是从文献中。计算了$_{2}$ [s]和SiO[s]的晶种形成速率，发现它们在T $_{\rm gas}$ = 1000-1750 K的高温下有效地成核。发现Cr[s]、KCl[s]和NaCl[s]在T $_{\rm gas}$ = 500-1000 K的中间温度范围内有效地成核。我们发现CsCl[s]可能是冷亚恒星大气中水云层的种子粒子。本文还研究了最冷的亚恒星/行星大气中四种低温冰（H $_{2}$ O[s/l]，NH $_{3}$ [s]，H $_{2}$ S[s/l]和CH $_{4}$ [s]）的成核率（T $_{\rm gas}$ = 100-250 K）。我们的结果表明，在整个亚恒星和行星大气温压空间中，种子粒子形成机制可能存在（T $_{\rm gas}$，p $_{\rm gas}$）分布层次结构。为了提高成核率计算的准确性，需要进一步研究每种云的小团簇热化学数据。这些种子粒子场景的有效性将在未来通过将其应用于更完整的云模型来进行测试。

英文摘要：

The cloud formation process starts with the formation of seed particles, after which, surface chemical reactions grow or erode the cloud particles. We investigate which materials may form cloud condensation seeds in the gas temperature and pressure regimes (T$_{\rm gas}$ = 100-2000 K, p$_{\rm gas}$ = 10$^{-8}$-100 bar) expected to occur in planetary and brown dwarf atmospheres. We apply modified classical nucleation theory which requires surface tensions and vapour pressure data for each solid species, which are taken from the literature. We calculate the seed formation rates of TiO$_{2}$[s] and SiO[s] and find that they efficiently nucleate at high temperatures of T$_{\rm gas}$ = 1000-1750 K. Cr[s], KCl[s] and NaCl[s] are found to efficiently nucleate across an intermediate temperature range of T$_{\rm gas}$ = 500-1000 K. We find CsCl[s] may serve as the seed particle for the water cloud layers in cool sub-stellar atmospheres. Four low temperature ice species, H$_{2}$O[s/l], NH$_{3}$[s], H$_{2}$S[s/l] and CH$_{4}$[s], nucleation rates (T$_{\rm gas}$ = 100-250 K) are also investigated for the coolest sub-stellar/planetary atmospheres. Our results suggest a possibly, (T$_{\rm gas}$, p$_{\rm gas}$) distributed hierarchy of seed particle formation regimes throughout the sub-stellar and planetary atmospheric temperature-pressure space. In order to improve the accuracy of the nucleation rate calculation, further research into the small cluster thermochemical data for each cloud species is warranted. The validity of these seed particle scenarios will be tested by applying it to more complete cloud models in the future.

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