A Comparative L-dwarf Sample Exploring the Interplay Between Atmospheric Assumptions and Data Properties

© 2022. The Author(s). Published by the American Astronomical Society. This is an open access article distributed under the Creative Commons Attribution License, to view a copy of the license, see: https://creativecommons.org/licenses/by/4.0/Comparisons of atmospheric retrievals can reveal powerful insights on the strengths and limitations of our data and modeling tools. In this paper, we examine a sample of 5 similar effective temperature (Teff) or spectral type L dwarfs to compare their pressure-temperature (P-T) profiles. Additionally, we explore the impact of an object's metallicity and the observations' signal-to-noise (SNR) on the parameters we can retrieve. We present the first atmospheric retrievals: 2MASS J15261405$+$2043414, 2MASS J05395200$-$0059019, 2MASS J15394189$-$0520428, and GD 165B increasing the small but growing number of L-dwarfs retrieved. When compared to atmospheric retrievals of SDSS J141624.08+134826.7, a low-metallicity d/sdL7 primary in a wide L+T binary, we find similar Teff sources have similar P-T profiles with metallicity differences impacting the relative offset between their P-T profiles in the photosphere. We also find that for near-infrared spectra, when the SNR is $\gtrsim80$ we are in a regime where model uncertainties dominate over data measurement uncertainties. As such, SNR does not play a role in the retrieval's ability to distinguish between a cloud-free and cloudless model, but may impact the confidence of the retrieved parameters. Lastly, we also discuss how to break cloud model degeneracies and the impact of extraneous gases in a retrieval model.Peer reviewe

Properties of the T8.5 Dwarf Wolf 940 B

We present 7.5-14.2um low-resolution spectroscopy, obtained with the Spitzer Infrared Spectrograph, of the T8.5 dwarf Wolf 940 B, which is a companion to an M4 dwarf with a projected separation of 400 AU. We combine these data with previously published near-infrared spectroscopy and mid-infrared photometry, to produce the spectral energy distribution for the very low-temperature T dwarf. We use atmospheric models to derive the bolometric correction and obtain a luminosity of log L/Lsun = -6.01 +/- 0.05. Evolutionary models are used with the luminosity to constrain the values of effective temperature (T_eff) and surface gravity, and hence mass and age for the T dwarf. We further restrict the allowed range of T_eff and gravity using age constraints implied by the M dwarf primary, and refine the physical properties of the T dwarf by comparison of the observed and modelled spectroscopy and photometry. This comparison indicates that Wolf 940 B has a metallicity within 0.2 dex of solar, as more extreme values give poor fits to the data - lower metallicity produces a poor fit at lambda > 2um while higher metallicity produces a poor fit at lambda < 2um. This is consistent with the independently derived value of [m/H] = +0.24 +/- 0.09 for the primary star, using the Johnson & Apps (2008) M_K:V-K relationship. We find that the T dwarf atmosphere is undergoing vigorous mixing, with an eddy diffusion coefficient K_zz of 10^4 to 10^6 cm^2 s^-1. We derive an effective temperature of 585 K to 625 K, and surface gravity log g = 4.83 to 5.22 (cm s^-2), for an age range of 3 Gyr to 10 Gyr, as implied by the kinematic and H alpha properties of the M dwarf primary. The lower gravity corresponds to the lower temperature and younger age for the system, and the higher value to the higher temperature and older age. The mass of the T dwarf is 24 M_Jupiter to 45 M_Jupiter for the younger to older age limit.Comment: 24 pages which include 5 Figures and 3 Tables. Accepted for publication in the Astrophysical Journal July 2 201

Predicting Cloud Conditions in Substellar Mass Objects Using Ultracool Dwarf Companions

© 2024 The Author(s). Published by the American Astronomical Society. 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/We present results from conducting a theoretical chemical analysis of a sample of benchmark companion brown dwarfs whose primary star is of type F, G or K. We summarize the entire known sample of these types of companion systems, termed "compositional benchmarks", that are present in the literature or recently published as key systems of study in order to best understand brown dwarf chemistry and condensate formation. Via mass balance and stoichiometric calculations, we predict a median brown dwarf atmospheric oxygen sink of $17.8^{+1.7}_{-2.3}\%$ by utilizing published stellar abundances in the local solar neighborhood. Additionally, we predict a silicate condensation sequence such that atmospheres with bulk Mg/Si $\lesssim$ 0.9 will form enstatite (MgSiO$_3$) and quartz (SiO$_2$) clouds and atmospheres with bulk Mg/Si $\gtrsim$ 0.9 will form enstatite and forsterite (Mg$_2$SiO$_4$) clouds. Implications of these results on C/O ratio trends in substellar mass objects and utility of these predictions in future modeling work are discussed.Peer reviewe

Developing an economic led approach to zero carbon housing design through integration and substitution of traditional building materials

Zero carbon homes have met with mixed reactions from key stakeholders within the housing and energy sectors, with many bespoke zero carbon designs being rejected as commercially unviable. This paper draws on research conducted with The University of Surrey and Zedfactory Architects to outline key factors which should be considered in order to facilitate the adoption of a more commercialised approach to zero carbon design. Key design criteria for zero carbon homes are outlined before presenting a housing model designed to provide the best balance between the financial, technical and social elements involved. The paper then demonstrates the importance of reducing the additional costs associated with zero carbon design through integrating energy efficiency and generation technologies into the building fabric; by substituting the use of traditional building materials with energy generating ones it is possible to create both an energy and economically efficient housing model. The proposed energy system adopts an integrated approach to the selection of space heating, water heating and ventilation technologies in order to create a design that is as user friendly as possible. By adopting this approach it is argued that it is possible to develop a model which does not require major changes in household behaviour patterns to work. The paper also highlights the importance of carefully balancing energy production and exportation to grid connected sources to develop a zero carbon home that can substantially reduce the financial burdens of rising energy costs

Parallaxes of Five L Dwarfs with a Robotic Telescope

We report the parallax and proper motion of five L dwarfs obtained with observations from the robotic Liverpool Telescope. Our derived proper motions are consistent with published values and have considerably smaller errors. Based on our spectral type versus absolute magnitude diagram, we do not find any evidence for binaries among our sampleor, at least no comparable mass binaries. Their space velocities locate them within the thin disk, and based on the model comparisons, they have solar-like abundances. For all five objects, we derived effective temperature, luminosity, radius, gravity, and mass from an evolutionary model (CBA00) and our measured parallax; moreover, we derived their effective temperature by integrating observed optical and near-infrared spectra and model spectra (BSH06 or BT-Dusty) at longer wavelengths to obtain bolometric flux using the classical Stefan-Boltzmann law. Generally, the three temperatures for one object derived using two different methods with three models are consistent, although at lower temperature (e.g., for L4) the differences among the three temperatures are slightly larger than those at higher temperature (e.g., for L1).Peer reviewe

Spitzer Mid-Infrared Photometry of 500 - 750 K Brown Dwarfs

Mid-infrared data, including Spitzer warm-IRAC [3.6] and [4.5] photometry, is critical for understanding the cold population of brown dwarfs now being found, objects which have more in common with planets than stars. As effective temperature (T_eff) drops from 800 K to 400 K, the fraction of flux emitted beyond 3 microns increases rapidly, from about 40% to >75%. This rapid increase makes a color like H-[4.5] a very sensitive temperature indicator, and it can be combined with a gravity- and metallicity-sensitive color like H-K to constrain all three of these fundamental properties, which in turn gives us mass and age for these slowly cooling objects. Determination of mid-infrared color trends also allows better exploitation of the WISE mission by the community. We use new Spitzer Cycle 6 IRAC photometry, together with published data, to present trends of color with type for L0 to T10 dwarfs. We also use the atmospheric and evolutionary models of Saumon & Marley to investigate the masses and ages of 13 very late-type T dwarfs, which have H-[4.5] > 3.2 and T_eff ~ 500 K to 750 K.Comment: To be published in the on-line version of the Proceedings of Cool Stars 16 (ASP Conference Series). This is an updated version of Leggett et al. 2010 ApJ 710 1627; a photometry compilation is available at http://www.gemini.edu/staff/slegget

ACCESS Guiding Principles V4 - March 2023

This is the final version.Navigating the Guiding Principles: The Guiding Principles are intended to act both as a guide to core ACCESS activity (in a non-prescriptive way) and as inspiration for the wider Environmental Social Science research, policy and practice communities. We anticipate the Guiding Principles will be developed over time as we receive input from others and reflect upon and learn from our own experiences within ACCESS. These pages – which are not intended to be exhaustive in terms of resources and encouraged actions – have 5 main sections: 1. An Introduction to ACCESS’s three Guiding Principles: Environmental Sustainability (ES); Equality, Diversity and Inclusion (EDI); and Knowledge Co-Production (KCP) 2. An outline of the Core Elements of each of the three Guiding Principles 3. Principles into Practice – a guide through the process of how and when to operationalise and incorporate ES, EDI, and KCP considerations into your ACCESS activities 4. Signposts to Further Resources for each of the three Guiding Principles 5. Activity Matrices – an outline of how the Guiding Principles can be applied to key activities that colleagues and partners undertake across ACCESS, with a range of suggested considerations and encouraged actions for each principle. We have identified nine key activities or areas of work to specifically address (although the focus on these key work areas does not preclude the Guiding Principles from being applied to other activities conducted across ACCESS). These core work areas are: I. Internal meetings II. Workshops and Events III. Communication 5 IV. Working Groups V. Recruitment (employees; participants at ‘applied for’ events) VI. Flex Fund Administration VII. Externally-facing training VIII. People development within ACCESS IX. Research ActivitiesEconomic and Social Research Council (ESRC)

Retrieval of the d/sdL7+T7.5p Binary SDSS J1416+1348AB

We present the distance-calibrated spectral energy distribution (SED) of the d/sdL7 SDSS J14162408+1348263A (J1416A) and an updated SED for SDSS J14162408+1348263B (J1416B). We also present the first retrieval analysis of J1416A using the Brewster retrieval code base and the second retrieval of J1416B. We find that the primary is best fit by a nongray cloud opacity with a power-law wavelength dependence but is indistinguishable between the type of cloud parameterization. J1416B is best fit by a cloud-free model, consistent with the results from Line et al. Most fundamental parameters derived via SEDs and retrievals are consistent within 1σ for both J1416A and J1416B. The exceptions include the radius of J1416A, where the retrieved radius is smaller than the evolutionary model-based radius from the SED for the deck cloud model, and the bolometric luminosity, which is consistent within 2.5σ for both cloud models. The pair\u27s metallicity and carbon-to-oxygen ratio point toward formation and evolution as a system. By comparing the retrieved alkali abundances while using two opacity models, we are able to evaluate how the opacities behave for the L and T dwarf. Lastly, we find that relatively small changes in composition can drive major observable differences for lower-temperature objects

An Atmospheric Retrieval of the Brown Dwarf Gliese 229B

© 2022. The Author(s). Published by the American Astronomical Society. This is an open access article distributed under the Creative Commons Attribution License, to view a copy of the license, see: https://creativecommons.org/licenses/by/4.0/We present results from an atmospheric retrieval analysis of Gl 229B using the Brewster retrieval code. We find the best fit model to be cloud-free, consistent with the T dwarf retrieval work of Line et al.; Zalesky et al. and Gonzales et al. Fundamental parameters (mass, radius, log(L Bol /L Sun), log(g)) determined from our model agree within 1σ to SED-derived values, except for T eff where our retrieved T eff is approximately 100 K cooler than the evolutionary model-based SED value. We find a retrieved mass of 50−9+12 M Jup, however, we also find that the observables of Gl 229B can be explained by a cloud-free model with a prior on mass at the dynamical value, 70 M Jup . We are able to constrain abundances for H2O, CO, CH4, NH3, Na and K and find a supersolar C/O ratio as compared to its primary, Gl 229A. We report an overall subsolar metallicity due to atmospheric oxygen depletion, but find a solar [C/H], which matches that of the primary. We find that this work contributes to a growing trend in retrieval-based studies, particularly for brown dwarfs, toward supersolar C/O ratios and discuss the implications of this result on formation mechanisms and internal physical processes, as well as model biases.Peer reviewe