TY - JOUR
T1 - Cloud busting
T2 - Enstatite and quartz clouds in the atmosphere of 2M2224-0158
AU - Burningham, Ben
AU - Faherty, Jacqueline K.
AU - Gonzales, Eileen C.
AU - Marley, Mark S.
AU - Visscher, Channon
AU - Lupu, Roxana
AU - Gaarn, Josefine
AU - Fabienne Bieger, Michelle
AU - Freedman, Richard
AU - Saumon, Didier
N1 - Funding Information:
BB acknowledges financial support from the European Commission in the form of a Marie Curie International Outgoing Fellowship (PIOF-GA-2013- 629435). This research was made possible thanks to the Royal Society International Exchange grant no. IES/R3/170266. EG acknowledges support for this work by the NSF under grant no. AST-1614527 and grant no. AST-1313278 and by NASA under Kepler grant no. 80NSSC19K0106. MFB and JG acknowledge support UK Research and Innovation-Science and Technology Facilities Council (UKRI-STFC) studentships. This work made use of SCIPY (Virtanen et al. 2020), NUMPY (Harris et al. 2020), and MATPLOTLIB, a PYTHON library for publication quality graphics (Hunter 2007), as well as ASTROPY, a community-developed core PYTHON package for Astronomy (Astropy Collaboration 2013, 2018). Brewster also relies on the F2PY package (Peterson 2009).We thank the anonymous referee for a helpful review which improved the quality of this manuscript.
Publisher Copyright:
© 2021 The Author(s) 2021. Published by Oxford University Press on behalf of Royal Astronomical Society.
PY - 2021/9/1
Y1 - 2021/9/1
N2 - We present the most detailed data-driven exploration of cloud opacity in a substellar object to-date. We have tested over 60 combinations of cloud composition and structure, particle-size distribution, scattering model, and gas phase composition assumptions against archival 1-15μm spectroscopy for the unusually red L4.5 dwarf 2MASSW J2224438-015852 using the Brewster retrieval framework. We find that, within our framework, a model that includes enstatite and quartz cloud layers at shallow pressures, combined with a deep iron cloud deck fits the data best. This model assumes a Hansen distribution for particle sizes for each cloud, and Mie scattering. We retrieved particle effective radii of log10 a(μm) = -1.41+0.18-0.17 for enstatite, -0.44+0.04-0.20 for quartz, and -0.77+0.05-0.06 for iron. Our inferred cloud column densities suggest (Mg/Si) = 0.69+0.06-0.08 if there are no other sinks for magnesium or silicon. Models that include forsterite alongside, or in place of, these cloud species are strongly rejected in favour of the above combination. We estimate a radius of 0.75 ± 0.02 RJup, which is considerably smaller than predicted by evolutionary models for a field age object with the luminosity of 2M2224-0158. Models which assume vertically constant gas fractions are consistently preferred over models that assume thermochemical equilibrium. From our retrieved gas fractions, we infer [M/H] = +0.38+0.07-0.06 and C/O = 0.83+0.06-0.07. Both these values are towards the upper end of the stellar distribution in the Solar neighbourhood, and are mutually consistent in this context. A composition towards the extremes of the local distribution is consistent with this target being an outlier in the ultracool dwarf population.
AB - We present the most detailed data-driven exploration of cloud opacity in a substellar object to-date. We have tested over 60 combinations of cloud composition and structure, particle-size distribution, scattering model, and gas phase composition assumptions against archival 1-15μm spectroscopy for the unusually red L4.5 dwarf 2MASSW J2224438-015852 using the Brewster retrieval framework. We find that, within our framework, a model that includes enstatite and quartz cloud layers at shallow pressures, combined with a deep iron cloud deck fits the data best. This model assumes a Hansen distribution for particle sizes for each cloud, and Mie scattering. We retrieved particle effective radii of log10 a(μm) = -1.41+0.18-0.17 for enstatite, -0.44+0.04-0.20 for quartz, and -0.77+0.05-0.06 for iron. Our inferred cloud column densities suggest (Mg/Si) = 0.69+0.06-0.08 if there are no other sinks for magnesium or silicon. Models that include forsterite alongside, or in place of, these cloud species are strongly rejected in favour of the above combination. We estimate a radius of 0.75 ± 0.02 RJup, which is considerably smaller than predicted by evolutionary models for a field age object with the luminosity of 2M2224-0158. Models which assume vertically constant gas fractions are consistently preferred over models that assume thermochemical equilibrium. From our retrieved gas fractions, we infer [M/H] = +0.38+0.07-0.06 and C/O = 0.83+0.06-0.07. Both these values are towards the upper end of the stellar distribution in the Solar neighbourhood, and are mutually consistent in this context. A composition towards the extremes of the local distribution is consistent with this target being an outlier in the ultracool dwarf population.
KW - Stars: brown dwarfs
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U2 - 10.1093/mnras/stab1361
DO - 10.1093/mnras/stab1361
M3 - Article
AN - SCOPUS:85111213093
VL - 506
SP - 1944
EP - 1961
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
SN - 0035-8711
IS - 2
ER -