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        The first retrieval of a substellar subdwarf: A cloud-free SDSS J125637.13-022452.4

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        2109.11000v1.pdf (PDF, 10Mb)(embargoed until 08/12/2022)
        Author
        Gonzales, Eileen C.
        Burningham, Ben
        Faherty, Jacqueline K.
        Visscher, Channon
        Marley, Mark S.
        Lupu, Roxana
        Freedman, Richard
        Lewis, Nikole K.
        Attention
        2299/25310
        Abstract
        We present the first retrieval analysis of a substellar subdwarf, SDSS J125637.13-022452.4 (SDSS J1256-0224), using the Brewster retrieval code base. We find SDSS J1256-0224 is best fit by a cloud-free model with an ion (neutral H, H-, and electron) abundance corresponding to ion [Fe/H]=-1.5. However, this model is indistinguishable from a cloud-free model with ion [Fe/H]=-2.0 and a cloud-free model with ion Fe/H]=-1.5 assuming a subsolar carbon-to-oxygen ratio. We are able to constrain abundances for water, FeH, and CrH, with an inability to constrain any carbon-bearing species likely due to the low-metallicity of SDSS J1256-0224. We also present an updated spectral energy distribution (SED) and semi-empirical fundamental parameters. Our retrieval- and SED-based fundamental parameters agree with the Baraffe low-metallicity evolutionary models. From examining our "rejected" models (those with $\Delta$BIC>45), we find that we are able to retrieve gas abundances consistent with those of our best-fitting model. We find the cloud in these poorer fitting "cloudy" models is either pushed to the bottom of the atmosphere or made optically thin.
        Publication date
        2021-12-08
        Published in
        The Astrophysical Journal
        Published version
        https://doi.org/10.3847/1538-4357/ac294e
        Other links
        http://hdl.handle.net/2299/25310
        Relations
        School of Physics, Engineering & Computer Science
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