The JWST Early Release Science Program for Direct Observations of Exoplanetary Systems. V. Do Self-consistent Atmospheric Models Represent JWST Spectra? A Showcase with VHS 1256–1257 b
Simon Petrus, Niall Whiteford, Polychronis Patapis, Beth Biller, Andrew Skemer, Sasha Hinkley, Genaro Suárez, P. Palma-Bifani, Caroline Morley, Pascal Tremblin, Benjamin Charnay, Johanna M. Vos, Jason Wang, Jordan Stone, M. Bonnefoy, G. Chauvin, Brittany Miles, Aarynn L. Carter, Anna Lueber, Ch. Helling, Ben J. Sutlieff, M. Janson, Eileen C. Gonzales, Kielan K. W. Hoch, Olivier Absil, William O. Balmer, A. Boccaletti, M. Bonavita, Mark Booth, Brendan P. Bowler, Zackery Briesemeister, Marta L. Bryan, Per Calissendorff, F. Cantalloube, Christine Chen, Élodie Choquet, Valentin Christiaens, Gabriele Cugno, Thayne Currie, Camilla Danielski, Matthew De Furio, Trent J. Dupuy, Samuel M. Factor, Jacqueline K. Faherty, Michael P. Fitzgerald, Jonathan J. Fortney, Kyle Franson, J. H. Girard, C. A. Grady, Thomas Henning, Dean C. Hines, Callie E. Hood, Alex R. Howe, Paul Kalas, Jens Kammerer, Grant M. Kennedy, Matthew A. Kenworthy, P. Kervella, M. Kim, Daniel Kitzmann, Adam L. Kraus, Masayuki Kuzuhara, Pierre-Olivier Lagage, A.‐M. Lagrange, Kellen Lawson, C. Lazzoni, Jarron Leisenring, Ben W. P. Lew, Michael C. Liu, Pengyu Liu, Jorge Llop-Sayson, James P. Lloyd, Bruce Macintosh, Mathilde Mâlin, Elena Manjavacas, Sebastián Marino, Mark S. Marley, Christian Marois, Raquel A. Martinez, Elisabeth C. Matthews, Brenda C. Matthews, Dimitri Mawet, Johan Mazoyer, Michael W. McElwain, Stanimir Metchev, Michael R. Meyer, Maxwell A. Millar‐Blanchaer, P. Mollière, Sarah E. Moran, Sagnick Mukherjee, E. Pantin, Marshall D. Perrin, Laurent Pueyo, Sascha P. Quanz, A. Quirrenbach, Shrishmoy Ray, Isabel Rebollido, Jéa Adams Redai, Bin Ren, Emily Rickman
Abstract
Abstract The unprecedented medium-resolution ( R λ ∼ 1500–3500) near- and mid-infrared (1–18 μ m) spectrum provided by JWST for the young (140 ± 20 Myr) low-mass (12–20 M Jup ) L–T transition (L7) companion VHS 1256 b gives access to a catalog of molecular absorptions. In this study, we present a comprehensive analysis of this data set utilizing a forward-modeling approach applying our Bayesian framework, ForMoSA . We explore five distinct atmospheric models to assess their performance in estimating key atmospheric parameters: T eff , log( g ), [M/H], C/O, γ , f sed , and R . Our findings reveal that each parameter’s estimate is significantly influenced by factors such as the wavelength range considered and the model chosen for the fit. This is attributed to systematic errors in the models and their challenges in accurately replicating the complex atmospheric structure of VHS 1256 b, notably the complexity of its clouds and dust distribution. To propagate the impact of these systematic uncertainties on our atmospheric property estimates, we introduce innovative fitting methodologies based on independent fits performed on different spectral windows. We finally derived a T eff consistent with the spectral type of the target, considering its young age, which is confirmed by our estimate of log( g ). Despite the exceptional data quality, attaining robust estimates for chemical abundances [M/H] and C/O, often employed as indicators of formation history, remains challenging. Nevertheless, the pioneering case of JWST’s data for VHS 1256 b has paved the way for future acquisitions of substellar spectra that will be systematically analyzed to directly compare the properties of these objects and correct the systematics in the models.