Retrieval of atmospheric properties of cloudy L dwarfs

© 2017 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.We present the first results from applying the spectral inversion technique in the cloudy L dwarf regime. Our new framework provides a flexible approach to modelling cloud opacity which can be built incrementally as the data requires, and improves upon previous retrieval experiments in the brown dwarf regime by allowing for scattering in two stream radiative transfer. Our first application of the tool to two mid-L dwarfs is able to reproduce their near-infrared spectra far more closely than grid models. Our retrieved thermal, chemical, and cloud profiles allow us to estimate $T_{\rm eff} = 1796^{+23}_{-25}$ K and $\log g = 5.21^{+0.05}_{-0.08}$ for 2MASS J05002100+0330501 and for 2MASSW J2224438-015852 we find $T_{\rm eff} = 1723^{+18}_{-19}$ K and $\log g = 5.31^{+0.04}_{-0.08}$, in close agreement with previous empirical estimates. Our best model for both objects includes an optically thick cloud deck which passes $\tau_{cloud} \geq 1$ (looking down) at a pressure of around 5 bar. The temperature at this pressure is too high for silicate species to condense, and we argue that corundum and/or iron clouds are responsible for this cloud opacity. Our retrieved profiles are cooler at depth, and warmer at altitude than the forward grid models that we compare, and we argue that some form of heating mechanism may be at work in the upper atmospheres of these L dwarfs. We also identify anomalously high CO abundance in both targets, which does not correlate with the warmth of our upper atmospheres or our choice of cloud model, and find similarly anomalous alkali abundance for one of our targets. These anomalies may reflect unrecognised shortcomings in our retrieval model, or inaccuracies in our gas phase opacities.Peer reviewedFinal Accepted Versio

Women and urban environments, volume 1 : feminist analysis of urban spaces

vii, 58 p. : ill

A research agenda on Data Supply Chains (DSC)

Competition among organizations supports initiatives and collaborative use of data while creating value based on the strategy and best performance of each data supply chain. Supporting this direction, and building on the theoretical background of the supply chain, we propose the Data Supply Chain (DSC) as a novel concept to aid investigations for data-driven collaboration impacting organizational performance. In this study we initially propose a definition for the DSC paying particular attention to the need for collaboration for the supply chains of data. Furthermore, we develop a conceptual model of DSC collaboration coupling theoretical background of strategy and operations literature including, the resource-based view (RBV), supply chain management (SCM) and collaboration (SCC). Finally, we set propositions and a future research agenda including testing and validating the model fit

Data Supply Chain (DSC): development and validation of a measurement instrument

The volume and availability of data produced and affordably stored has become an important new resource for building organizational competitive advantage. Reflecting this, and expanding the concept of the supply chain, we propose the Data Supply Chain (DSC) as a novel concept to aid investigations into how the interconnected data characteristics relate to and impact organizational performance. Initially, we define the concept and develop a research agenda on DSC coupling theoretical background of strategy and operations literature. Along with the conceptualization, we develop a set of propositions and make suggestions for future research including testing and validating the model fit

First Report on Alternative Evaluation Methodology PROMISE Deliverable 4.1

The first report on alternative evaluation methodology summarizes work done within the PROMISE environment and especially within Work package 4 - Evaluation Metrics and Methodologies. The report outlines efforts to develop and support alternative, automated evaluation methodologies, with a special focus on generating ground truth from existing data sources like Log files or annotations. Events like LogCLEF 2011, PatOlympics 2011 or the CHiC2011 workshop are presented and reviewed on their impact on the three main uses case domains

The Sonora Substellar Atmosphere Models. II. Cholla: A Grid of Cloud-free, Solar Metallicity Models in Chemical Disequilibrium for the JWST Era

Exoplanet and brown dwarf atmospheres commonly show signs of disequilibrium chemistry. In the James Webb Space Telescope (JWST) era, high-resolution spectra of directly imaged exoplanets will allow the characterization of their atmospheres in more detail, and allow systematic tests for the presence of chemical species that deviate from thermochemical equilibrium in these atmospheres. Constraining the presence of disequilibrium chemistry in these atmospheres as a function of parameters such as their effective temperature and surface gravity will allow us to place better constraints on the physics governing these atmospheres. This paper is part of a series of works presenting the Sonora grid of atmosphere models. In this paper, we present a grid of cloud-free, solar metallicity atmospheres for brown dwarfs and wide-separation giant planets with key molecular species such as CH4, H2O, CO, and NH3 in disequilibrium. Our grid covers atmospheres with Teff ä [500 K, 1300 K], log g ä [3.0, 5.5] (cgs) and an eddy diffusion parameter of log 2, 4 Kzz = and 7 (cgs). We study the effect of different parameters within the grid on the temperature and composition profiles of our atmospheres. We discuss their effect on the near-infrared colors of our model atmospheres and the detectability of CH4, H2O, CO, and NH3 using the JWST. We compare our models against existing MKO and Spitzer observations of brown dwarfs and verify the importance of disequilibrium chemistry for T dwarf atmospheres. Finally, we discuss how our models can help constrain the vertical structure and chemical composition of these atmospheres

Sonora: A New Generation Model Atmosphere Grid for Brown Dwarfs and Young Extrasolar Giant Planets

Brown dwarf and giant planet atmospheric structure and composition has been studied both by forward models and, increasingly so, by retrieval methods. While indisputably informative, retrieval methods are of greatest value when judged in the context of grid model predictions. Meanwhile retrieval models can test the assumptions inherent in the forward modeling procedure. In order to provide a new, systematic survey of brown dwarf atmospheric structure, emergent spectra, and evolution, we have constructed a new grid of brown dwarf model atmospheres. We ultimately aim for our grid to span substantial ranges of atmospheric metallilcity, C/O ratios, cloud properties, atmospheric mixing, and other parameters. Spectra predicted by our modeling grid can be compared to both observations and retrieval results to aid in the interpretation and planning of future telescopic observations. We thus present Sonora, a new generation of substellar atmosphere models, appropriate for application to studies of L, T, and Y-type brown dwarfs and young extrasolar giant planets. The models describe the expected temperature-pressure profile and emergent spectra of an atmosphere in radiative-convective equilibrium for ranges of effective temperatures and gravities encompassing 200 less than or equal to T(sub eff) less than or equal to 2400 K and 2.5 less than or equal to log g less than or equal to 5.5. In our poster we briefly describe our modeling methodology, enumerate various updates since our group's previous models, and present our initial tranche of models for cloudless, solar metallicity, and solar carbon-to-oxygen ratio, chemical equilibrium atmospheres. These models will be available online and will be updated as opacities and cloud modeling methods continue to improve