Details

Autor(en) / Beteiligte

• Petrus, S.
• Chauvin, G.
• Bonnefoy, M.
• Tremblin, P.
• Charnay, B.
• Delorme, P.
• Marleau, G.-D.
• Bayo, A.
• Manjavacas, E.
• Lagrange, A.-M.
• Mollière, P.
• Palma-Bifani, P.
• Biller, B.
• Jenkins, J.-S.
• Goyal, J.-M.
• Hoch, K.

Titel

X-SHYNE: X-shooter spectra of young exoplanet analogs: I. A medium-resolution 0.65–2.5 μ m one-shot spectrum of VHS 1256−1257 b

Ist Teil von

• Astronomy and astrophysics (Berlin), 2023-02, Vol.670, p.L9

Ort / Verlag

EDP Sciences

Erscheinungsjahr

2023

Quelle

EZB Electronic Journals Library

Beschreibungen/Notizen

• We present simultaneous 0.65–2.5 μm medium resolution (3300 ≤  R λ  ≤ 8100) VLT/X-shooter spectra of the relatively young (150–300 Myr) low-mass (19 ± 5 M Jup ) L–T transition object VHS 1256−1257 b, a known spectroscopic analog of HR8799d. The companion is a prime target for the JWST Early Release Science (ERS) and one of the highest-amplitude variable brown dwarfs known to date. We compare the spectrum to the custom grids of cloudless ATMO models, exploring the atmospheric composition with the Bayesian inference tool ForMoSA . We also reanalyze low-resolution HST/WFC3 1.10–1.67 μm spectra at minimum and maximum variability to contextualize the X-shooter data interpretation. The models reproduce the slope and most molecular absorption from 1.10 to 2.48 μm self-consistently, but they fail to provide a radius and a surface gravity consistent with evolutionary model predictions. They do not reproduce the optical spectrum and the depth of the K I doublets in the J band consistently. We derived T eff = 1380±54 K, log( g ) = 3.97±0.48 dex, [M/H] = 0.21±0.29, and C/O > 0.63. Our inversion of the HST/WFC3 spectra suggests a relative change of $ 27^{+6}_{-5} $ K of the disk-integrated T eff correlated with the near-infrared brightness. Our data anchor the characterization of that object in the near-infrared and could be used jointly to the ERS mid-infrared data to provide the most detailed characterization of an ultracool dwarf to date.