The effect of thermal non-equilibrium on kinetic nucleation

Abstract

Nucleation is considered to be the first step in dust and cloud formation in the atmospheres of asymptotic giant branch (AGB) stars, exoplanets, and brown dwarfs. In these environments dust and cloud particles grow to macroscopic sizes when gas phase species condense onto cloud condensation nuclei (CCNs). Understanding the formation processes of CCNs and dust in AGB stars is important because the species that formed in their outflows enrich the interstellar medium. Although widely used, the validity of chemical and thermal equilibrium conditions is debatable in some of these highly dynamical astrophysical environments. We aim to derive a kinetic nucleation model that includes the effects of thermal non-equilibrium by adopting different temperatures for nucleating species, and to quantify the impact of thermal non-equilibrium on kinetic nucleation. Forward and backward rate coefficients are derived as part of a collisional kinetic nucleation theory ansatz. The endothermic backward rates are derived from the law of mass action in thermal non-equilibrium. We consider elastic collisions as thermal equilibrium drivers. For homogeneous TiO2 nucleation and a gas temperature of 1250 K, we find that differences in the kinetic cluster temperatures as small as 20 K increase the formation of larger TiO2 clusters by over an order of magnitude. An increase in cluster temperature of around 20 K at gas temperatures of 1000 K can reduce the formation of a larger TiO2 cluster by over an order of magnitude. Our results confirm and quantify the prediction of previous thermal non-equilibrium studies. Small thermal non-equilibria can cause a significant change in the synthesis of larger clusters. Therefore, it is important to use kinetic nucleation models that include thermal non-equilibrium to describe the formation of clusters in environments where even small thermal non-equilibria can be present.

arXiv comment13 pages, 4 figures

References in corpus (31)

• The Limiting Effects of Dust in Brown Dwarf Model Atmospheres
• A continuum from clear to cloudy hot-Jupiter exoplanets without primordial water depletion
• Clouds in the atmosphere of the super-Earth exoplanet GJ 1214b
• Precipitating Condensation Clouds in Substellar Atmospheres
• Detection of atmospheric haze on an extrasolar planet: The 0.55 - 1.05 micron transmission spectrum of HD189733b with the Hubble Space Telescope
• The prevalence of dust on the exoplanet HD 189733b from Hubble and Spitzer observations
• Radiation thermo-chemical models of protoplanetary disks I. Hydrostatic disk structure and inner rim
• A ground-based transmission spectrum of the super-Earth exoplanet GJ1214b
• HST hot-Jupiter transmission spectral survey: detection of potassium in WASP-31b along with a cloud deck and Rayleigh scattering
• The global gas and dust budget of the Large Magellanic Cloud: AGB stars and supernovae, and the impact on the ISM evolution
• Dust formation in the oxygen-rich AGB star IK Tau
• Hubble Space Telescope Near-IR Transmission Spectroscopy of the Super-Earth HD 97658b
• Dust in Brown Dwarfs and Extra-solar Planets I. Chemical composition and spectral appearance of quasi-static cloud layers
• Dust in the Photospheric Environment: Unified Cloudy Models of M, L, and T Dwarfs
• A Detailed Analysis of the Dust Formation Zone of IRC+10216 Derived from Mid-IR Bands of C2H2 and HCN
• Dust in the Photospheric Environment III. A Fundamental Element in the Characterization of Ultracool Dwarfs
• New insights into the dust formation of oxygen-rich AGB stars
• Warm Ice Giant GJ 3470b. I. A Flat Transmission Spectrum Indicates a Hazy, Low-methane, and/or Metal-rich Atmosphere
• Radiative cooling functions for primordial molecules
• Dusty tails of evaporating exoplanets. I. Constraints on the dust composition
• Bottom-up dust nucleation theory in oxygen-rich evolved stars I. Aluminium oxide clusters
• Developing a self-consistent AGB wind model: II. Non-classical, non-equilibrium polymer nucleation in a chemical mixture
• Dust Formation in Astrophysical Environments: The Importance of Kinetics
• The abundance of C2H4 in the circumstellar envelope of IRC+10216
• Revisiting fundamental properties of TiO${}_2$ nanoclusters as condensation seeds in astrophysical environments
• On the relative velocity distribution for general statistics and an application to big-bang nucleosynthesis under Tsallis statistics
• Non-LTE dust nucleation in sub-saturated vapors
• The nature of HHL 73 from optical imaging and Integral Field Spectroscopy
• Dust in brown dwarfs and extra-solar planets. VIII. TiO${}_2$ seed formation: 3D Monte Carlo versus kinetic approach
• Multi-frequency high spectral resolution observations of HCN toward the circumstellar envelope of Y CVn
• Thermodynamics of the Condensation of Dust Grains in Wolf-Rayet Stellar Winds

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• Why heterogeneous cloud particles matter: Iron-bearing species and cloud particle morphology affects exoplanet transmission spectra
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• The Mechanics of Nucleation and Growth and the Surface Tensions of Active Matter
• Under the magnifying glass: A combined 3D model applied to cloudy warm Saturn type exoplanets around M-dwarfs