TY - JOUR
T1 - Toward Robust Atmospheric Retrieval on Cloudy L Dwarfs
T2 - the Impact of Thermal and Abundance Profile Assumptions
AU - Rowland, Melanie J.
AU - Morley, Caroline V.
AU - Line, Michael R.
N1 - Funding Information:
The authors acknowledge the Texas Advanced Computing Center (TACC) at The University of Texas at Austin for providing high-performance computing resources that have contributed to the research results reported within this paper. URL: http://www.tacc.utexas.edu . M.J.R. acknowledges funding from NASA FINESST grant No. 80NSSC20K1550. C.V.M. acknowledges funding from National Science Foundation AAG grant No. 1910969.
Funding Information:
The authors acknowledge the Texas Advanced Computing Center (TACC) at The University of Texas at Austin for providing high-performance computing resources that have contributed to the research results reported within this paper. URL: http://www.tacc.utexas.edu. M.J.R. acknowledges funding from NASA FINESST grant No. 80NSSC20K1550. C.V.M. acknowledges funding from National Science Foundation AAG grant No. 1910969.
Publisher Copyright:
© 2023. The Author(s). Published by the American Astronomical Society.
PY - 2023/4/1
Y1 - 2023/4/1
N2 - Constraining L dwarf properties from their spectra is challenging. Near-infrared (NIR) spectra probe a limited range of pressures, while many species condense within their photospheres. Condensation creates two complexities: gas-phase species “rain out” (decreasing in abundances by many orders of magnitude) and clouds form. We designed tests using synthetic data to determine the best approach for retrieving L dwarf spectra, isolating the challenges in the absence of cloud opacity. We conducted atmospheric retrievals on synthetic cloud-free L dwarf spectra derived from the Sonora Bobcat models at SpeX resolution using a variety of thermal and chemical abundance profile parameterizations. For objects hotter than L5 (T eff ∼ 1700 K), the limited pressure layers probed in the NIR are mostly convective; parameterized pressure-temperature (PT) profiles bias results and free, unsmoothed profiles should be used. Only when many layers both above and below the radiative-convective boundary are probed can parameterized profiles provide accurate results. Furthermore, a nonuniform abundance profile for FeH is needed to accurately retrieve bulk properties of early-to-mid L dwarfs. Nonuniform prescriptions for other gases in NIR retrievals may also be warranted near the L/T transition (CH4) and early Y dwarfs (Na and K). We demonstrate the utility of using realistic, self-consistent models to benchmark retrievals and suggest how they can be used in the future.
AB - Constraining L dwarf properties from their spectra is challenging. Near-infrared (NIR) spectra probe a limited range of pressures, while many species condense within their photospheres. Condensation creates two complexities: gas-phase species “rain out” (decreasing in abundances by many orders of magnitude) and clouds form. We designed tests using synthetic data to determine the best approach for retrieving L dwarf spectra, isolating the challenges in the absence of cloud opacity. We conducted atmospheric retrievals on synthetic cloud-free L dwarf spectra derived from the Sonora Bobcat models at SpeX resolution using a variety of thermal and chemical abundance profile parameterizations. For objects hotter than L5 (T eff ∼ 1700 K), the limited pressure layers probed in the NIR are mostly convective; parameterized pressure-temperature (PT) profiles bias results and free, unsmoothed profiles should be used. Only when many layers both above and below the radiative-convective boundary are probed can parameterized profiles provide accurate results. Furthermore, a nonuniform abundance profile for FeH is needed to accurately retrieve bulk properties of early-to-mid L dwarfs. Nonuniform prescriptions for other gases in NIR retrievals may also be warranted near the L/T transition (CH4) and early Y dwarfs (Na and K). We demonstrate the utility of using realistic, self-consistent models to benchmark retrievals and suggest how they can be used in the future.
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U2 - 10.3847/1538-4357/acbb07
DO - 10.3847/1538-4357/acbb07
M3 - Article
AN - SCOPUS:85152573541
SN - 0004-637X
VL - 947
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 1
M1 - 6
ER -