Self-consistent atmosphere modeling with cloud formation for low-mass stars and exoplanets

Abstract

Context. Low-mass stars and extrasolar planets have ultra-cool atmospheres where a rich chemistry occurs and clouds form. The increasing amount of spectroscopic observations for extrasolar planets requires self-consistent model atmosphere simulations to consistently include the formation processes that determine cloud formation and their feedback onto the atmosphere. Aims. Complement the Marcs model atmosphere suit with simulations applicable to low-mass stars and exoplanets in preparation of E-ELT, JWST, PLATO and other upcoming facilities. Methods. The Marcs code calculates stellar atmosphere models, providing self-consistent solutions of the radiative transfer and the atmospheric structure and chemistry. We combine Marcs with a kinetic model that describes cloud formation in ultra-cool atmospheres (seed formation, growth/ evaporation, gravitational settling, convective mixing, element depletion). Results. We present a small grid of self-consistently calculated atmosphere models for T eff = 2000 − 3000 K with solar initial abundances and log(g) = 4.5. Cloud formation in stellar and sub-stellar atmospheres appears for T eff < 2700 K and has a significant effect on the structure and the spectrum of the atmosphere for T eff < 2400 K. We have compared the synthetic spectra of our models with observed spectra and found that they fit the spectra of mid to late type M-dwarfs and early type L-dwarfs well. The geometrical extension of the atmospheres (at τ = 1) changes with wavelength resulting in a flux variation of ∼10%. This translates into a change in geometrical extension of the atmosphere of about 50 km, which is the quantitative basis for exoplanetary transit spectroscopy. We also test Drift-Marcs for an example exoplanet and demonstrate that our simulations reproduce the Spitzer observations for WASP-19b rather well for T eff = 2600K, log(g) = 3.2 and solar abundances. Our model points at an exoplanet with a deep cloud-free atmosphere with a substantial day-night energy transport and no temperature inversion.

Dynamics of dusty vortices – I. Extensions and limitations of the terminal velocity approximation

“…Dominik et al 1989;Höfner & Olofsson 2018), and planetary and substellar atmospheres (e.g. Juncher et al 2017;Johnas et al 2008;Taylor et al 2007) as well as in protoplanetary discs. The behaviour of dust in such a mixture can be understood as an ensemble of dust particles feeling the external fields, as well as a drag force from the surrounding gas.…”

The impact of mixing treatments on cloud modelling in 3D simulations of hot Jupiters

“…Barstow et al 2017;Fisher & Heng 2018;Pinhas et al 2019), to parameterisations attempting to capture the basic physics (e.g., Ackerman & Marley 2001, hereafter termed the E -S model) to more sophisticated microphysical approaches (e.g. Juncher et al 2017;Powell et al 2019). However, there is a growing realisation that 1D models are insufficient to correctly capture the physical state of, in particular, short period exoplanets such as hot Jupiters.…”

Understanding the atmospheric properties and chemical composition of the ultra-hot Jupiter HAT-P-7b

“…Currently, none of the models for HAT-P-7b have included the effect of cloud formation. Clouds affect the local gas phase through element depletion and enrichment, and as strong opacity sources that affect the local temperature (Lunine et al 1986;Tsuji et al 1996;Ackerman & Marley 2001;Allard et al 2001;Witte et al 2009;Lee et al 2015aLee et al , 2016Juncher et al 2017;Lines et al 2018b). Clouds can also strongly impact thermal emission and reflected light spectra, transit observations, and phase curves.…”