Multi-modal Atmospheric Characterization Of beta Pictoris b: Adding High-resolution Continuum Spectra From GRAVITY

We present the first VLTI/GRAVITY observations at R_λ∼4000 of β Pic b. These four high S/N (∼20) K-band spectra conserve both the pseudo-continuum and molecular absorption patterns.

We analyze them with four self-consistent forward model grids (Exo-REM, ATMO, BT-Settl, Sonora) exploring T_eff, log(g), metallicity, C/O, and ¹²CO/¹³CO ratio. We also upgrade our forward modeling code ForMoSA-5 μm photometry, low- to medium-resolution spectra (0.9-7 μm), and high-resolution echelle spectra (2.1-5.2 μm).

Sonora and Exo-REM are statistically preferred. Exo-REM yields T_eff =1607.45+4.85−6.20 K and log(g) =4.46+0.02−0.04 dex from GRAVITY alone, and T_eff =1502.74+2.32−2.14 K and log(g) =4.00±0.01 dex when including all datasets.

Archival data significantly affect the retrieved parameters. C/O remains solar (0.552+0.003−0.002) while [M/H] reaches super-solar values (0.50±0.01). We report the first tentative constraint on log(¹²CO/¹³CO ) ∼1.12, though this remains inconclusive due to telluric residuals.

Additionally, we estimate the luminosity to be log(L/L_⊙) =−4.01+0.04−0.05, implying a heavy-element content of up to ∼5% (20-80 M_⊕) given the system age and dynamical mass measurements. Access to both continuum and molecular lines at K-band significantly impacts the metallicity, possibly owing to collision-induced absorption shaping the continuum. Echelle spectra do not dominate the final fit with respect to lower resolution data. Future multi-modal frameworks should include weighting schemes reflecting bandwidth and central wavelength coverage.

M. Ravet, M. Bonnefoy, G. Chauvin, S. Lacour, M. Nowak, B. Charnay, P. Tremblin, D. Homeier, C. Morley, J. Fortney, A. Denis, S. Petrus, P. Palma-Bifani, R. Landman, L. T. Parker, M. Houllé, A. Chomez, K. Worthen, F. Kiefer, G.-D. Marleau, Z. Zhang, J. L. Birkby, F. Millour, A.-M. Lagrange, A. Vigan, G.P.P.L. Otten, J. Shangguan

Comments: Accepted for publication in A&A
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2509.25338 [astro-ph.EP] (or arXiv:2509.25338v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2509.25338
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Submission history
From: Matthieu Ravet
[v1] Mon, 29 Sep 2025 18:00:22 UTC (2,448 KB)
https://arxiv.org/abs/2509.25338
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