Atmospheric abundances and bulk properties of the binary brown dwarf Gliese 229 Bab from JWST/MIRI spectroscopy
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| Format: | Preprint |
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2024
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| author | Xuan, Jerry W. Perrin, Marshall D. Mawet, Dimitri Knutson, Heather A. Mukherjee, Sagnick Zhang, Yapeng Hoch, Kielan K. Wang, Jason J. Inglis, Julie Wallack, Nicole L. Ruffio, Jean-Baptiste |
| author_facet | Xuan, Jerry W. Perrin, Marshall D. Mawet, Dimitri Knutson, Heather A. Mukherjee, Sagnick Zhang, Yapeng Hoch, Kielan K. Wang, Jason J. Inglis, Julie Wallack, Nicole L. Ruffio, Jean-Baptiste |
| contents | We present JWST/MIRI low-resolution spectroscopy ($4.75-14~μ$m) of the first known substellar companion, Gliese 229 Bab, which was recently resolved into a tight binary brown dwarf. Previous atmospheric retrieval studies modeling Gliese 229 B as a single brown dwarf have reported anomalously high carbon-to-oxygen ratios (C/O) of $\approx 1.1$ using $1-5~μ$m ground-based spectra. Here, we fit the MIRI spectrum of Gliese 229 Bab with a two-component binary model using the Sonora Elf Owl grid and additionally account for the observed $K$ band flux ratio of the binary brown dwarf. Assuming the two brown dwarfs share the same abundances, we obtain $\rm C/O=0.65\pm0.05$ and $\rm [M/H]=0.00^{+0.04}_{-0.03}$ as their abundances ($2σ$ statistical errors), which are fully consistent with the host star abundances. We also recover the same abundances if we fit the MIRI spectrum with a single brown dwarf model, indicating that binarity does not strongly affect inferred abundances from mid-infrared data when the $T_\rm{eff}$ are similar between components of the binary. We measure $T_\rm{eff}=900^{+78}_{-29}~$K and $T_\rm{eff}=775^{+20}_{-33}~$K for the two brown dwarfs. We find that the vertical diffusion coefficients of $\log{K_\rm{zz}} \approx4.0$ are identical between the two brown dwarfs and in line with $\log{K_\rm{zz}}$ values inferred for isolated brown dwarfs with similar $T_\rm{eff}$. Our results demonstrate the power of mid-infrared spectroscopy in providing robust atmospheric abundance measurements for brown dwarf companions and by extension, giant planets. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2411_10571 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Atmospheric abundances and bulk properties of the binary brown dwarf Gliese 229 Bab from JWST/MIRI spectroscopy Xuan, Jerry W. Perrin, Marshall D. Mawet, Dimitri Knutson, Heather A. Mukherjee, Sagnick Zhang, Yapeng Hoch, Kielan K. Wang, Jason J. Inglis, Julie Wallack, Nicole L. Ruffio, Jean-Baptiste Solar and Stellar Astrophysics Earth and Planetary Astrophysics We present JWST/MIRI low-resolution spectroscopy ($4.75-14~μ$m) of the first known substellar companion, Gliese 229 Bab, which was recently resolved into a tight binary brown dwarf. Previous atmospheric retrieval studies modeling Gliese 229 B as a single brown dwarf have reported anomalously high carbon-to-oxygen ratios (C/O) of $\approx 1.1$ using $1-5~μ$m ground-based spectra. Here, we fit the MIRI spectrum of Gliese 229 Bab with a two-component binary model using the Sonora Elf Owl grid and additionally account for the observed $K$ band flux ratio of the binary brown dwarf. Assuming the two brown dwarfs share the same abundances, we obtain $\rm C/O=0.65\pm0.05$ and $\rm [M/H]=0.00^{+0.04}_{-0.03}$ as their abundances ($2σ$ statistical errors), which are fully consistent with the host star abundances. We also recover the same abundances if we fit the MIRI spectrum with a single brown dwarf model, indicating that binarity does not strongly affect inferred abundances from mid-infrared data when the $T_\rm{eff}$ are similar between components of the binary. We measure $T_\rm{eff}=900^{+78}_{-29}~$K and $T_\rm{eff}=775^{+20}_{-33}~$K for the two brown dwarfs. We find that the vertical diffusion coefficients of $\log{K_\rm{zz}} \approx4.0$ are identical between the two brown dwarfs and in line with $\log{K_\rm{zz}}$ values inferred for isolated brown dwarfs with similar $T_\rm{eff}$. Our results demonstrate the power of mid-infrared spectroscopy in providing robust atmospheric abundance measurements for brown dwarf companions and by extension, giant planets. |
| title | Atmospheric abundances and bulk properties of the binary brown dwarf Gliese 229 Bab from JWST/MIRI spectroscopy |
| topic | Solar and Stellar Astrophysics Earth and Planetary Astrophysics |
| url | https://arxiv.org/abs/2411.10571 |