J/A+A/704/A325 beta Pictoris b spectra (Ravet+, 2025)
Multimodal atmospheric characterization of beta Pictoris b.
Adding high-resolution continuum spectra from GRAVITY.
Ravet M., Bonnefoy M., Chauvin G., Lacour S., Nowak M., Charnay B.,
Tremblin P., Homeier D., Morley C., Fortney J., Denis A., Petrus S.,
Palma-Bifani P., Landman R., Parker L.T., Houlle M., Chomez A., Worthen K.,
Kiefer F., Marleau G.-D., Zhang Z., Birkby J.L., Millour F., Lagrange A.-M.,
Vigan A., Otten G.P.P.L., Shangguan J.
<Astron. Astrophys. 704, A325 (2025)>
=2025A&A...704A.325R 2025A&A...704A.325R (SIMBAD/NED BibCode)
ADC_Keywords: Stars, double and multiple ; Exoplanets ; Spectra, infrared
Keywords: instrumentation: spectrographs - methods: data analysis -
techniques: interferometric - techniques: spectroscopic -
planets and satellites: atmospheres -
planets and satellites: gaseous planets
Abstract:
Characterizations of giant exoplanets such as beta Pictoris b
(hereafter beta Pic b) are now routinely performed with multiple
spectrographs and imagers exploring different spectral bandwidths and
resolutions, allowing for atmospheric retrieval of spectra with or
without the conservation of the planet spectral continuum. The
accounting of data multimodality in the analysis could provide a more
comprehensive determination of the planets physical and chemical
properties and inform on their formation history.
We present the first VLTI observations at Rλ∼4000 of beta Pic b
obtained for an exoplanet with GRAVITY at such a high resolution. We
upgraded the forward modelling code ForMoSA to account for the data
multimodality, including low-, medium-, and high-resolution
spectroscopy based on both a direct model-data comparison and an
analysis of cross-correlation signals. We used the ForMoSA code to
refine the constraints on the atmospheric properties of the exoplanet
and evaluated the sensitivity of the retrieved values to the input
dataset.
We obtained four high-signal-to-noise (S/N∼20) spectra of beta Pic b
in the K band with GRAVITY at Rλ ∼4000 conserving both the
pseudo-continuum and the pattern of molecular absorptions. We used
ForMoSA with four grids of self-consistent forward models (Exo-REM,
ATMO, BT-Settl, and Sonora) to explore different Teff, log(g),
metallicity, C/O, and 12CO/13CO ratio values. We then combined the
GRAVITY spectra with published 1-5um photometry (NaCo, VisAO, NICI,
and SPHERE), low-to-mediumresolution (Rλ≤700 broadband,
0.9-7um) spectra, and echelle spectra covering narrower bandwidths
(Rλ∼100000, 2.1-5.2um).
Sonora and Exo-REM are statistically preferred among all four models,
regardless of the dataset used. Exo-REM predicts
Teff=1607.45-6.20+4.85K and log(g)=4.46_-0.04+0.02 dex when using
only the GRAVITY epochs, whereas we have Teff = 1502.74-2.14+2.32K
and log(g)=4.00±0.01dex when incorporating all available datasets.
The inclusion of archival data significantly affects all retrieved
posteriors. When using all datasets, C/O mostly remains solar
(0.552-0.002+0.003), while [M/H] reaches super-solar values
(0.50±0.01). We report the first tentative constraint on the
isotopic ratio log(12CO/13CO)=1.12-0.08+0.11 in beta Pic b;s
atmosphere; however, we note that this detection remains inconclusive
due to telluric residuals affecting both the GRAVITY and SINFONI data.
Additionally, we estimated the bolometric luminosity as
log(L/L☉)=-4.01-0.05+0.04dex. Using a system age of
23±3Myr, along with this bolometric luminosity and the constraints
on the dynamical mass of beta Pic b, we were able to constrain the
maximum of heavy element content of the planet to be on the order of
5% (20-80M⊕).
The joint access to the pseudo-continuum and molecular lines in the K
band provided by GRAVITY have a significant impact on the retrieved
metallicity, possibly owing to the collision-induced absorption
driving the continuum shape of the K band. The echelle spectra do not
dominate the final fit with respect to lower resolution data covering
a broader portion of the spectral energy distribution and the latter
keeps encapsulating more robust information on Teff. Future multimodal
frameworks should include a weighting scheme to account for the
bandwidth and central wavelength of the observations.
Description:
We present the first VLTI/GRAVITY observations at R∼4000 of beta
Pictoris b. These high S/N K-band spectra preserve both continuum and
molecular absorption features. We combined GRAVITY epochs with
published photometry, low- to medium- resolution spectra
(0.9-7 microns) and high-resolution echelle spectra (2.1-5.2 microns).
The data consist of 18 spectra + photometric points in *.fits. Among
them, all low- to medium- resolution spectra are flux calibrated in
W/m2/micron with a wavelength grid in microns. CRIRES+ observations
are separated by date and nod and the flux are in arbitrary units.
Each .fits contains the date and the name of the instrument either in
the abstract (for spectra) or in the column ['INSTRUMENT']. Default
columns are 'WAVELENGTH', 'FLUX' and 'ERROR'. Additionnal columns are
'RESOLUTION' (spectral), 'TRANSMISSION' (atmospheric), 'STAR_FLX',
'SYSTEMATICS', 'COVARIANCE' and 'INSTRUMENTS' .
Objects:
-------------------------------------------------------
RA (2000) DE Designation(s)
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05 47 17.08 -51 03 59.4 beta Pictoris = HD 39060
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 139 18 List of fits spectra
fits/* . 18 Individual fits spectra
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See also:
J/A+A/607/A25 : beta Pic HARPS spectrum (Vidal-Madjar+, 2017)
J/A+A/627/A28 : beta Pic BRITE, bRing, SMEI light curves (Zwintz+, 2019)
Byte-by-byte Description of file: list.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
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1- 8 F8.5 deg RAdeg Right Ascension of center (J2000)
9- 17 F9.5 deg DEdeg Declination of center (J2000)
18- 22 I5 --- Nx Number of pixels along X-axis
24- 28 I5 --- Ny Number of pixels along Y-axis
30- 39 A10 "datime" Obs.date Observation date
41- 45 I5 Kibyte size Size of FITS file
47- 91 A45 --- FileName Name of FITS file, in subdirectory fits
93-139 A47 --- Title Title of the FITS file
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Acknowledgements:
Matthieu Ravet, matthieu.ravet18(at)gmail.com
(End) Patricia Vannier [CDS] 04-Dec-2025