Characterization of Exoplanet Atmospheres with the Optical Coronagraph on WFIRST

WFIRST-CGI is a NASA technology demonstration mission that is charged with demonstrating key technologies for future exo-Earth imaging missions in space. In the process, it will obtain images and low-resolution spectra of a handful to a dozen extrasolar planets and possibly protoplanetary disks. Its unprecedented contrast levels in the optical will provide astronomers with their first direct look at mature, Jupiter sized planets at moderate separations. This paper addresses the question: what science can be done with such data? An analytic noise model, which is informed by the ongoing engineering developments, is used to compute maximum achievable signal-to-noise ratios and scientifically viable integration times for hypothetical star planet systems, as well as to investigate the constraining power of various combinations of WFIRST-CGI photometric and spectral observations. This work introduces two simple models for planetary geometric albedos, which are inspired largely by the solar system's gas giants. The first planet model is a hybrid Jupiter-Neptune model, which separately treats the short and long wavelengths where chromophores and methane dominate absorption, respectively. The second planet model fixes cloud and haze properties in CoolTLusty to match Jupiter's albedo spectrum, it then perturbs only the metallicity. MCMC retrievals performed on simulated observations are used to assess the precision with which planet model parameters can be measured subject to different exposure times and observing cases. Fit results for both models' parameterizations of geometric albedo spectra demonstrate that a rough indication of the metallicity or methane content should be possible for some WFIRST-CGI targets. We conclude that real observations will likely be able to differentiate between extreme cases using these models, but will lack the precision necessary to uncover subtle trends.Comment: 29 pages, 25 figures, 2 table

Self-consistent Models of Y Dwarf Atmospheres with Water Clouds and Disequilibrium Chemistry

Y dwarfs are the coolest spectral class of brown dwarf. They have effective temperatures less than 500 K, with the coolest detection as low as ~250 K. Their spectra are shaped predominantly by gaseous water, methane, and ammonia. At the warmer end of the Y dwarf temperature range, spectral signatures of disequilibrium carbon monoxide have been observed. Cooler Y dwarfs could host water clouds in their atmospheres. Since they make up the low-mass tail of the star formation process, and are a valuable analogue to the atmospheres of giant gaseous exoplanets in a temperature range that is difficult to observe, understanding Y dwarf atmospheric compositions and processes will both deepen our understanding of planet and star formation, and provide a stepping stone towards characterizing cool exoplanets. JWST spectral observations are anticipated to provide an unprecedented level of detail for these objects, and yet published self-consistent model grids do not accurately replicate even the existing HST and ground-based observations. In this work, we present a new suite of 1-d radiative-convective equilibrium models to aid in the characterization of Y dwarf atmospheres and spectra. We compute clear, cloudy, equilibrium-chemistry and disequilibrium-chemistry models, providing a comprehensive suite of models in support of the impending JWST era of panchromatic Y dwarf characterization. Comparing these models against current observations, we find that disequilibrium CH4-CO and NH3-N2 chemistry and the presence of water clouds can bring models and observations into better, though still not complete, agreement.Comment: main text: 27 pages, 19 figures, 4 tables; appendix + references: 13 pages, 3 figures, 4 tables; model grid available on zenodo https://doi.org/10.5281/zenodo.777918

Harvest of the Month for Early Childhood Education: Parent Perspectives

The purpose of this research brief is to report on the impact of Harvest of the Month (HOM) for Early Care and Education (ECE) at home to better understand parent perspectives and influences on children’s nutrition behavior. Harvest of the Month (HOM) is a farm to school programming strategy that features a locally grown food in at least one nutrition and agriculture lesson, taste test activity, and a snack or meal recipe each month. This exploratory study used a survey research design to gather parent perspectives during pilot implementation of HOM for ECE during the 2017 – 2018 school year. The survey was delivered electronically. Twenty-one parents from a campus-based preschool program in the northwest United States reported procurement and consumption of HOM foods at home. Findings suggest that a variety of HOM foods are being served and consumed at home. Parents in this study placed more importance on knowing where food comes from rather than serving local foods. Further, parents’ knowledge of farm to ECE, reported food purchasing at farmer’s markets, and participation in community-supported agriculture (CSA) programs were limited, suggesting a need for continued targeted parent education that could have a positive effect of families’ healthy eating

Methane Emission From a Cool Brown Dwarf

© 2024, The Author(s). This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY), https://creativecommons.org/licenses/by/4.0/Beyond our solar system, aurorae have been inferred from radio obser- vations of isolated brown dwarfs (e.g. [1]; [2]). Within our solar system, giant planets have auroral emission with signatures across the electromag- netic spectrum including infrared emission of H3+ and methane. Isolated brown dwarfs with auroral signatures in the radio have been searched for corresponding infrared features but have only had null detections (e.g. [3]). CWISEP J193518.59-154620.3. (W1935 for short) is an isolated brown dwarf with a temperature of ∼482 K. Here we report JWST observations of strong methane emission from W1935 at 3.326 microns. Atmospheric mod- eling leads us to conclude that a temperature inversion of ∼300 K centered at 1-10 millibar replicates the feature. This represents an atmospheric tem- perature inversion for a Jupiter-like atmosphere without irradiation from a host star. A plausible explanation for the strong inversion is heating by auroral processes, although other internal and/or external dynamical pro- cesses cannot be ruled out. The best fit model rules out the contribution of H3+ emission which is prominent in solar system gas giants, however this is consistent with rapid destruction of H3+ at the higher pressure where the W1935 emission originates (e.g. [4]).Peer reviewe

Windows into Alien Worlds: Modeling and Characterizing Substellar Atmospheres

Atmospheres constitute the only accessible layer for observation from space, and their properties are linked to objects' formation and evolution, surface and interior processes, and habitability. Exoplanets and brown dwarfs are difficult to observe, but they provide a vast and varied data set which compliments insights gleaned from the small number of Solar System planets. This dissertation encompasses a series of studies all related to modeling, observing, and understanding substellar atmospheres. I present results from four publications and one project still in progress, as well as a full update to the opacity tables paired with the atmosphere codes used in this work: coolTLUSTY and METIS. All studies put a particular emphasis on anticipating new insights that may be gained from upcoming missions: direct imaging of mature giant exoplanet's reflecting starlight and direct imaging of young self-luminous exoplanets with the optical coronagraph on the Nancy Grace Roman Space telescope, transit spectroscopy of cloudy, tidally-locked warm exoplanets with the James Webb Space Telescope, and finally spectra of cool Y dwarfs, also a prime target for the James Webb Space Telescope