4
Following Leggett et al. (2021), a larger grid of adiabat-adjusted models was generated for a study
ofmetal-poorbrowndwarfsbyMeisneretal.(2023). WerefertothismodelsetastheATMO2020++
models. Appendix A gives more information about these atmospheres, including how the parameters
were generalized from the smaller to the larger grid, and how the resulting synthetic SEDs compare.
The ATMO2020++ models generate colors which agree well with observations, as shown in Figures
2 and 3 of Meisner et al. (2023). We show below that the ATMO2020++ models perform extremely
well when compared to the continuous 1 ≤ λ µm ≤ 12 SED measured by JWST for a Y0 dwarf.
ATMO2020++ spectra are available at: the ERC-ATMO Opendata page.
3. THE FIRST JWST Y DWARF SPECTRUM
[m/H]=0
Figure 1. The black line is the observed spectrum of WISE 035934.06-540154.6 from Beiler et al. (2023).
Black points represent their photometric measurements. The pink line and dots are the best fit Sonora
model spectrum and photometry, from Beiler et al. The blue line and data points are the spectrum and
photometry from the best fit model of the ATMO2020++ grid. The green line is the same model where PH
3
has been removed from the atmospheric composition. The ATMO2020++ model is scaled by the known
distance to WISE 0359 (Kirkpatrick et al. 2021) and the radius inferred from evolutionary models (Marley
et al. 2021), and has not been scaled to fit. Principal opacity species are indicated. The lower panel shows
the difference between the observed spectrum and the spectra generated by the three models (note the
difference in y-axis scale in the upper and lower panels). The inset shows the near-infrared flux region. See
Section 3 for discussion.