Dynamically coupled kinetic chemistry in brown dwarf atmospheres I. Performing global scale kinetic modelling

The atmospheres of brown dwarfs have been long observed to exhibit a multitude of non-equilibrium chemical signatures and spectral variability across the L, T and Y spectral types. We aim to investigate the link between the large-scale 3D atmospheric dynamics and time-dependent chemistry in the brown dwarf regime, and to assess its impact on spectral variability. We couple the miniature kinetic chemistry module `mini-chem' to the Exo-FMS general circulation model (GCM). We then perform a series of idealised brown dwarf regime atmospheric models to investigate the dynamical 3D chemical structures produced by our simulations. The GCM output is post-processed using a 3D radiative-transfer model to investigate hemisphere-dependent spectral signatures and rotational variability. Our results show the expected strong non-equilibrium chemical behaviour brought on by vertical mixing as well as global spacial variations due to zonal flows. Chemical species are generally globally homogenised, showing variations of $\pm$10\% or less, dependent on pressure level, and follow the dynamical structures present in the atmosphere. However, we find localised storm regions and eddies can show higher contrasts, up to $\pm$100\%, in mixing ratio compared to the background global mean. This initial study represents another step in understanding the connection between three-dimensional atmospheric flows in brown dwarfs and their rich chemical inventories.Comment: MNRAS Accepted: 5 June 202

All along the line of sight: a closer look at opening angles and absorption regions in the atmospheres of transiting exoplanets

Transmission spectra contain a wealth of information about the atmospheres of transiting exoplanets. However, large thermal and chemical gradients along the line of sight can lead to biased inferences in atmospheric retrievals. In order to determine how far from the limb plane the atmosphere still impacts the transmission spectrum, we derive a new formula to estimate the opening angle of a planet. This is the angle subtended by the atmospheric region that contributes to the observation along the line of sight, as seen from the planet centre. We benchmark our formula with a 3D Monte Carlo radiative transfer code and we define an opening angle suitable for the interpretation of JWST observations, assuming a 10-ppm noise floor. We find that the opening angle is only a few degrees for planets cooler than ca. 500 Kelvins, while it can be as large as 25 degrees for (ultra-)hot Jupiters and 50 degrees for hot Neptunes. Compared to previous works, our more robust approach leads to smaller estimates for the opening angle across a wide range scale heights and planetary radii. Finally, we show that ultra-hot Jupiters have an opening angle that is smaller than the angle over which the planet rotates during the transit. This allows for time-resolved transmission spectroscopy observations that probe independent parts of the planetary limb during the first and second half of the transit

A Mini-Chemical Scheme with Net Reactions for 3D GCMs II. 3D thermochemical modelling of WASP-39b and HD 189733b

The chemical inventory of hot Jupiter (HJ) exoplanets atmospheres continue to be observed by various ground and space based instruments in increasing detail and precision. It is expected that some HJs will exhibit strong non-equilibrium chemistry characteristics in their atmospheres, which might be inferred from spectral observations. We aim to model the three dimensional thermochemical non-equilibrium chemistry in the atmospheres of the HJs WASP-39b and HD 189733b. We couple a lightweight, reduced chemical network `mini-chem' that utilises net reaction rate tables to the Exo-FMS General Circulation Model (GCM). We perform GCM models of the exoplanets WASP-39b and HD 189733b as case studies of the coupled mini-chem scheme. The GCM results are then post-processed using the 3D radiative-transfer model gCMCRT to produce transmission and emission spectra to assess the impact of non-equilibrium chemistry on their observable properties. Both simulations show significant departures from chemical equilibrium (CE) due to the dynamical motions of the atmosphere. The spacial distribution of species generally follows closely the dynamical features of the atmosphere rather than the temperature field. Each molecular species exhibits a different quench level in the simulations, also dependent on the latitude of the planet. Major differences are seen in the transmission and emission spectral features between the CE and kinetic models. Our simulations indicate that considering the 3D kinetic chemical structures of HJ atmospheres has an important impact on physical interpretation of observational data. Drawing bulk atmospheric parameters from fitting feature strengths may lead to inaccurate interpretation of chemical conditions in the atmosphere of HJs. Our open source mini-chem module is simple to couple with contemporary HJ GCM models without substantially increasing required computational resources.Comment: A&A Accepted 17 Feb 202

Modelling the effect of 3D temperature and chemistry on the cross-correlation signal of transiting ultra-hot Jupiters: A study of 5 chemical species on WASP-76b

Ultra-hot Jupiters are perfect targets for transmission spectroscopy. However, their atmospheres feature strong spatial variations in temperature, chemistry, dynamics, cloud coverage, and scale height. This makes transit observations at high spectral resolution challenging to interpret. In this work, we model the cross-correlation signal of five chemical species (Fe, CO, H$_\text{2}$O, OH, and TiO) on WASP-76b, a benchmark ultra-hot Jupiter. We compute phase-dependent high-resolution transmission spectra of 3D SPARC/MITgcm models. The spectra are obtained with gCMCRT, a 3D Monte-Carlo radiative-transfer code. We find that, on top of atmospheric dynamics, the phase-dependent Doppler shift of the absorption lines in the planetary rest frame is shaped by the combined effect of planetary rotation and the unique 3D spatial distribution of chemical species. For species probing the dayside (e.g., refractories or molecules like CO and OH), the two effects act in tandem, leading to increasing blueshifts with orbital phase. For species that are depleted on the dayside (e.g., H$_\text{2}$O and TiO), the two effects act in an opposite manner, and could lead to increasing redshifts during the transit. This behaviour yields species-dependent offsets from a planet's expected $K_\text{p}$ value that can be much larger than planetary wind speeds. The offsets are usually negative for refractory species. We provide an analytical formula to estimate the size of a planet's $K_\text{p}$ offsets, which can serve as a prior for atmospheric retrievals. We conclude that observing the phase-resolved absorption signal of multiple species is key to constraining the 3D thermochemical structure and dynamics of ultra-hot Jupiters.Comment: 21 pages, 14 figures, resubmitted to MNRAS after minor revision

Decomposing the Iron Cross-Correlation Signal of the Ultra-Hot Jupiter WASP-76b in Transmission using 3D Monte-Carlo Radiative Transfer

Ultra-hot Jupiters are tidally locked gas giants with dayside temperatures high enough to dissociate hydrogen and other molecules. Their atmospheres are vastly non-uniform in terms of chemistry, temperature and dynamics, and this makes their high-resolution transmission spectra and cross-correlation signal difficult to interpret. In this work, we use the SPARC/MITgcm global circulation model to simulate the atmosphere of the ultra-hot Jupiter WASP-76b under different conditions, such as atmospheric drag and the absence of TiO and VO. We then employ a 3D Monte-Carlo radiative transfer code, HIRES-MCRT, to self-consistently model high-resolution transmission spectra with iron (Fe I) lines at different phases during the transit. To untangle the structure of the resulting cross-correlation map, we decompose the limb of the planet into four sectors, and we analyse each of their contributions separately. Our experiments demonstrate that the cross-correlation signal of an ultra-hot Jupiter is primarily driven by its temperature structure, rotation and dynamics, while being less sensitive to the precise distribution of iron across the atmosphere. We also show that the previously published iron signal of WASP-76b can be reproduced by a model featuring iron condensation on the leading limb. Alternatively, the signal may be explained by a substantial temperature asymmetry between the trailing and leading limb, where iron condensation is not strictly required to match the data. Finally, we compute the $K_{p}-V_{sys}$ maps of the simulated WASP-76b atmospheres, and we show that rotation and dynamics can lead to multiple peaks that are displaced from zero in the planetary rest frame.Comment: Accepted for publication in MNRAS, 25 pages, 24 figure

The impact of face-to-face mental health consumer-led teaching on occupational therapy student empathy levels : Two group comparison design

Introduction Australian and New Zealand accreditation standards for occupational therapy courses mandate consumer involvement in the design, delivery, and evaluation of courses. Consumer involvement in medical, dental, and nursing education has been evidenced as a factor for increasing student empathy. To date, there has been no known research on the impact of mental health consumer involvement on occupational therapy students' empathy. The aim of this study was to investigate if occupational therapy students who receive teaching from a mental health consumer demonstrate higher levels of empathy compared with students who receive teaching delivered by occupational therapy academics. Methods Pre–post, quasi experimental, two group comparison design was used to measure second-year student empathy pre and post a consumer-led teaching tutorial. Students (N = 217) were randomised into two groups across three university campuses: ‘teaching as usual group’ (control) or ‘consumer-led’ group (experimental group). The Jefferson Scale of Empathy was used to measure student empathy. Results N = 138 matched scales were returned. Little difference in empathy scales was detected between groups. The ‘consumer-led’ group increased for the empathy scale by 3.4(95% CI: 0.7,6.1, p = 0.014) but was not statistically significant compared to 1.3(95% CI: −1.0,3.5, p = 0.267) for the control group. Both groups scored highly on empathy. Conclusion This study found that occupational therapy students had pre-existing high levels of empathy. The challenge for future research is to identify appropriate ways to measure the impact of mental health consumer involvement on occupational therapy curriculum and students

A Comparative Study of Atmospheric Chemistry with VULCAN

We present an update of the open-source photochemical kinetics code VULCAN (Tsai et al. 2017; this https URL) to include C-H-N-O-S networks and photochemistry. Additional new features are advection transport, condensation, various boundary conditions, and temperature-dependent UV cross-sections. First, we validate our photochemical model for hot Jupiter atmospheres by performing an intercomparison of HD 189733b models between Moses et al. (2011), Venot et al. (2012), and VULCAN, to diagnose possible sources of discrepancy. Second, we set up a model of Jupiter extending from the deep troposphere to upper stratosphere to verify the kinetics for low temperature. Our model reproduces hydrocarbons consistent with observations, and the condensation scheme successfully predicts the locations of water and ammonia ice clouds. We show that vertical advection can regulate the local ammonia distribution in the deep atmosphere. Third, we validate the model for oxidizing atmospheres by simulating Earth and find agreement with observations. Last, VULCAN is applied to four representative cases of extrasolar giant planets: WASP-33b, HD 189733b, GJ 436b, and 51 Eridani b. We look into the effects of the C/O ratio and chemistry of titanium/vanadium species for WASP-33b; we revisit HD 189733b for the effects of sulfur and carbon condensation; the effects of internal heating and vertical mixing (Kzz) are explored for GJ 436b; we test updated planetary properties for 51 Eridani b with S8 condensates. We find sulfur can couple to carbon or nitrogen and impact other species such as hydrogen, methane, and ammonia. The observable features of the synthetic spectra and trends in the photochemical haze precursors are discussed for each case

Understanding and Mitigating Biases when Studying Inhomogeneous Emission Spectra with JWST

Exoplanet emission spectra are often modelled assuming that the hemisphere observed is well represented by a horizontally homogenised atmosphere. However this approximation will likely fail for planets with a large temperature contrast in the James Webb Space Telescope (JWST) era, potentially leading to erroneous interpretations of spectra. We first develop an analytic formulation to quantify the signal-to-noise ratio and wavelength coverage necessary to disentangle temperature inhomogeneities from a hemispherically averaged spectrum. We find that for a given signal-to-noise ratio, observations at shorter wavelengths are better at detecting the presence of inhomogeneities. We then determine why the presence of an inhomogeneous thermal structure can lead to spurious molecular detections when assuming a fully homogenised planet in the retrieval process. Finally, we quantify more precisely the potential biases by modelling a suite of hot Jupiter spectra, varying the spatial contributions of a hot and a cold region, as would be observed by the different instruments of JWST/NIRSpec. We then retrieve the abundances and temperature profiles from the synthetic observations. We find that in most cases, assuming a homogeneous thermal structure when retrieving the atmospheric chemistry leads to biased results, and spurious molecular detection. Explicitly modelling the data using two profiles avoids these biases, and is statistically supported provided the wavelength coverage is wide enough, and crucially also spanning shorter wavelengths. For the high contrast used here, a single profile with a dilution factor performs as well as the two-profile case, with only one additional parameter compared to the 1-D approach.Comment: Accepted for publication by MNRA

How Does Thermal Scattering Shape the Infrared Spectra of Cloudy Exoplanets? A Theoretical Framework and Consequences for Atmospheric Retrievals in the JWST era

Observational studies of exoplanets are suggestive of a ubiquitous presence of clouds. The current modelling techniques used in emission to account for the clouds tend to require prior knowledge of the cloud condensing species and often do not consider the scattering effects of the cloud. We explore the effects that thermal scattering has on the emission spectra by modelling a suite of hot Jupiter atmospheres with varying cloud single-scattering albedos (SSAs) and temperature profiles. We examine cases ranging from simple isothermal conditions to more complex structures and physically driven cloud modelling. We show that scattering from nightside clouds would lead to brightness temperatures that are cooler than the real atmospheric temperature if scattering is unaccounted for. We show that scattering can produce spectral signatures in the emission spectrum even for isothermal atmospheres. We identify the retrieval degeneracies and biases that arise in the context of simulated JWST spectra when the scattering from the clouds dominates the spectral shape. Finally, we propose a novel method of fitting the SSA spectrum of the cloud in emission retrievals, using a technique that does not require any prior knowledge of the cloud chemical or physical properties.Comment: Accepted to MNRA