Panchromatic View of the Frigid Jovian Exoplanet COCONUTS-2 b
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| Format: | Preprint |
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2026
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| author | Ravet, Matthieu Bonnefoy, Mickaël Chauvin, Gaël Zhang, Zhoujian Faherty, Jacqueline K. Voyer, Maël Phillips, Mark W. Tremblin, Pascal Kiman, Rocio Copeland, Jessica Mang, James J. Morley, Caroline V. Kühnle, Helena Charnay, Benjamin de Regt, Sam Mollière, Paul Petrus, Simon Denis, Allan Radcliffe, Alice Palma-Bifani, Paulina Vigan, Arthur Mâlin, Mathilde Marleau, Gabriel-Dominique Manjavacas, Elena Hoy, Kevin Matthews, Elisabeth C. Henning, Thomas K. |
| author_facet | Ravet, Matthieu Bonnefoy, Mickaël Chauvin, Gaël Zhang, Zhoujian Faherty, Jacqueline K. Voyer, Maël Phillips, Mark W. Tremblin, Pascal Kiman, Rocio Copeland, Jessica Mang, James J. Morley, Caroline V. Kühnle, Helena Charnay, Benjamin de Regt, Sam Mollière, Paul Petrus, Simon Denis, Allan Radcliffe, Alice Palma-Bifani, Paulina Vigan, Arthur Mâlin, Mathilde Marleau, Gabriel-Dominique Manjavacas, Elena Hoy, Kevin Matthews, Elisabeth C. Henning, Thomas K. |
| contents | We use a high signal-to-noise MIRI-LRS spectrum (5.45 - 11 $μ$m, R$_λ$ $\sim100$) of COCONUTS-2~b revealing prominent molecular features of H$_2$O, CH$_4$ and NH$_3$. This dataset is combined with spectra from Gemini/FLAMINGOS-2 and JWST/NIRSpec (G395H), as well as photometry from WISE and Spitzer, resulting in almost continuous wavelength coverage from 1 to 15 $μ$m. We analyze the data using five grids of self-consistent atmospheric models, spanning a wide range of T$_\text{eff}$, log(g), and [M/H]. We also investigate the use of Gaussian Processes to account for correlated noise either caused by the spectrograph or by systematic departures of models in the inversion framework. All models manage to fit the overall combined observations but predict fainter flux in Y- and N-bands. Classical model comparison suggests that the ATMO2020++ synthetic specra (with and without PH$_3$) are statistically preferred. Fitting for the correlated noise of the three spectroscopic instruments, ATMO2020++ models yields constraints consistent with previous studies and evolutionary models predictions: T$_\text{eff}$ $=496^{+5}_{-3}$ K, log(g) $=4.30^{+0.04}_{-0.02}$ dex, [M/H] $=-0.02^{+0.03}_{-0.02}$ dex, and R $=1.03^{+0.01}_{-0.02}$ R$_\text{jup}$. The extended wavelength coverage provided by MIRI (accounting for 41% of the bolometric flux) completes the SED, yielding a precise luminosity estimation of log(L/L$_{\odot}$) $=-6.166\pm0.002$ dex. Combined with a previous estimate of the system age ($414\pm23$ Myr), cooling models predict a mass of M $=7.3\pm0.3$ M$_\text{jup}$. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2604_07176 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Panchromatic View of the Frigid Jovian Exoplanet COCONUTS-2 b Ravet, Matthieu Bonnefoy, Mickaël Chauvin, Gaël Zhang, Zhoujian Faherty, Jacqueline K. Voyer, Maël Phillips, Mark W. Tremblin, Pascal Kiman, Rocio Copeland, Jessica Mang, James J. Morley, Caroline V. Kühnle, Helena Charnay, Benjamin de Regt, Sam Mollière, Paul Petrus, Simon Denis, Allan Radcliffe, Alice Palma-Bifani, Paulina Vigan, Arthur Mâlin, Mathilde Marleau, Gabriel-Dominique Manjavacas, Elena Hoy, Kevin Matthews, Elisabeth C. Henning, Thomas K. Earth and Planetary Astrophysics We use a high signal-to-noise MIRI-LRS spectrum (5.45 - 11 $μ$m, R$_λ$ $\sim100$) of COCONUTS-2~b revealing prominent molecular features of H$_2$O, CH$_4$ and NH$_3$. This dataset is combined with spectra from Gemini/FLAMINGOS-2 and JWST/NIRSpec (G395H), as well as photometry from WISE and Spitzer, resulting in almost continuous wavelength coverage from 1 to 15 $μ$m. We analyze the data using five grids of self-consistent atmospheric models, spanning a wide range of T$_\text{eff}$, log(g), and [M/H]. We also investigate the use of Gaussian Processes to account for correlated noise either caused by the spectrograph or by systematic departures of models in the inversion framework. All models manage to fit the overall combined observations but predict fainter flux in Y- and N-bands. Classical model comparison suggests that the ATMO2020++ synthetic specra (with and without PH$_3$) are statistically preferred. Fitting for the correlated noise of the three spectroscopic instruments, ATMO2020++ models yields constraints consistent with previous studies and evolutionary models predictions: T$_\text{eff}$ $=496^{+5}_{-3}$ K, log(g) $=4.30^{+0.04}_{-0.02}$ dex, [M/H] $=-0.02^{+0.03}_{-0.02}$ dex, and R $=1.03^{+0.01}_{-0.02}$ R$_\text{jup}$. The extended wavelength coverage provided by MIRI (accounting for 41% of the bolometric flux) completes the SED, yielding a precise luminosity estimation of log(L/L$_{\odot}$) $=-6.166\pm0.002$ dex. Combined with a previous estimate of the system age ($414\pm23$ Myr), cooling models predict a mass of M $=7.3\pm0.3$ M$_\text{jup}$. |
| title | Panchromatic View of the Frigid Jovian Exoplanet COCONUTS-2 b |
| topic | Earth and Planetary Astrophysics |
| url | https://arxiv.org/abs/2604.07176 |