11:30 〜 11:45
[PCG19-10] Unveiling Atmospheric Features of HR 7672B Observed by REACH/Subaru
Characterizing the atmospheres of exoplanets and brown dwarfs is crucial for understanding their atmospheric physics and chemistry, searching for biosignatures, and investigating their formation histories. The observational method to combine adaptive optics with a high-resolution spectrograph has been developed recently, enabling high-resolution spectroscopy for directly imaged faint companions. This approach contrasts with lower-resolution spectroscopy, where atmospheric parameter degeneracy was a problem; high-resolution spectra enable precise identification of individual absorption lines, allowing for a detailed, non-degenerate examination of atmospheric characteristics.
In this research, we performed an atmospheric retrieval on the L-type brown dwarf HR 7672B, using the REACH (Y, J, H band, R∼100,000), which combines the SCExAO extreme adaptive optics instrument with the IRD infrared high-dispersion spectrograph at the Subaru Telescope. Our atmospheric models, calculated using the ExoJAX code (Kawahara et al. 2022), were enhanced by incorporating models for cloud presence in the brown dwarf atmosphere and accounting for contamination from host star light and Earth’s atmospheric absorption lines. The observed J and H band spectra were successfully fitted by the model including molecular species of H2O and FeH. We found that models both with and without cloud opacity could explain the observed spectra, attributed to varying continuum opacity sources (cloud or CIA opacity) under different temperature-pressure profiles. The model including cloud opacity suggests potential cloud formation from TiO2 or Al2O3. The retrieved H2O abundance is almost consistent with chemical equilibrium predictions, whereas the higher values of FeH might indicate a quenching process due to the atmospheric mixing.
Our presentation will outline the retrieval methodology, share our findings, and introduce future prospects.
In this research, we performed an atmospheric retrieval on the L-type brown dwarf HR 7672B, using the REACH (Y, J, H band, R∼100,000), which combines the SCExAO extreme adaptive optics instrument with the IRD infrared high-dispersion spectrograph at the Subaru Telescope. Our atmospheric models, calculated using the ExoJAX code (Kawahara et al. 2022), were enhanced by incorporating models for cloud presence in the brown dwarf atmosphere and accounting for contamination from host star light and Earth’s atmospheric absorption lines. The observed J and H band spectra were successfully fitted by the model including molecular species of H2O and FeH. We found that models both with and without cloud opacity could explain the observed spectra, attributed to varying continuum opacity sources (cloud or CIA opacity) under different temperature-pressure profiles. The model including cloud opacity suggests potential cloud formation from TiO2 or Al2O3. The retrieved H2O abundance is almost consistent with chemical equilibrium predictions, whereas the higher values of FeH might indicate a quenching process due to the atmospheric mixing.
Our presentation will outline the retrieval methodology, share our findings, and introduce future prospects.