University of Hertfordshire

From the same journal

From the same journal

By the same authors

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

Research output: Contribution to journalArticlepeer-review

  • Eileen C. Gonzales
  • Ben Burningham
  • Jacqueline K. Faherty
  • Channon Visscher
  • Mark S. Marley
  • Roxana Lupu
  • Richard Freedman
  • Nikole K. Lewis
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Original languageEnglish
Number of pages14
JournalThe Astrophysical Journal
Publication statusPublished - 8 Dec 2021


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.


© 2021. The American Astronomical Society. All rights reserved. This is the accepted manuscript version of an article which has been published in final form at

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