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Uniform Forward-modeling Analysis of Ultracool Dwarfs. I. Methodology and Benchmarking
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Zhang_2021_ApJ_916_53.pdf
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Zhang, Z., Liu, M. C., Marley, M. S., Line, M. R., & Best, W. M. J. (2021). Uniform Forward-modeling Analysis of Ultracool Dwarfs. I. Methodology and Benchmarking. Astrophysical Journal, 916(1).Journal
Astrophysical JournalRights
Copyright © 2021. The American Astronomical Society. All rights reserved.Collection Information
This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at repository@u.library.arizona.edu.Abstract
We present a forward-modeling framework using the Bayesian inference tool Starfish and cloudless Sonora-Bobcat model atmospheres to analyze low-resolution (R ≈ 80-250) near-infrared (1.0-2.5 μm) spectra of T dwarfs. Our approach infers effective temperatures, surface gravities, metallicities, radii, and masses, and by accounting for uncertainties from model interpolation and correlated residuals due to instrumental effects and modeling systematics, produces more realistic parameter posteriors than traditional (χ 2-based) spectral-fitting analyses. We validate our framework by fitting the model atmospheres themselves and finding negligible offsets between derived and input parameters. We apply our methodology to three well-known benchmark late-T dwarfs, HD 3651B, GJ 570D, and Ross 458C, using both solar and nonsolar metallicity atmospheric models. We also derive these benchmarks' physical properties using their bolometric luminosities, their primary stars' ages and metallicities, and Sonora-Bobcat evolutionary models. Assuming the evolutionary-based parameters are more robust, we find our atmospheric-based, forward-modeling analysis produces two outcomes. For HD 3615B and GJ 570D, spectral fits provide accurate T eff and R but underestimated log g (by ≈1.2 dex) and Z (by ≈0.35 dex), likely due to the systematics from modeling the potassium line profiles. For Ross 458C, spectral fits provide accurate log g and Z but overestimated T eff (by ≈120 K) and underestimated R (by ≈1.6×), likely because our model atmospheres lack clouds, reduced vertical temperature gradients, or disequilibrium processes. Finally, the spectroscopically inferred masses of these benchmarks are all considerably underestimated. © 2021. The American Astronomical Society. All rights reserved..Note
Immediate accessISSN
0004-637XVersion
Final published versionae974a485f413a2113503eed53cd6c53
10.3847/1538-4357/abf8b2