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

Eileen C. Gonzales, Ben Burningham, Jacqueline K. Faherty, Channon Visscher, Mark S. Marley, Roxana Lupu, Richard Freedman, Nikole K. Lewis

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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.
Original languageEnglish
Number of pages14
JournalThe Astrophysical Journal
Issue number1
Publication statusPublished - 8 Dec 2021


  • astro-ph.SR
  • astro-ph.EP


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