J/A+A/703/A70 WISEP J173835.52+273258.9 JWST/MIRI spectrum (Vasist+, 2025)
Panchromatic characterization of the Y0 brown dwarf WISEP J173835.52+273258.9
using JWST/MIRI.
Vasist M., Molliere P., Kuhnle H., Patapis P., Absil O., Louppe G.,
Lagage P.-O., Waters L.B.F.M., Gudel M., Henning T., Vandenbussche B.,
Barrado D., Decin L., Pye J.P., Tremblin P., Whiteford N.
<Astron. Astrophys. 703, A70 (2025)>
=2025A&A...703A..70V 2025A&A...703A..70V (SIMBAD/NED BibCode)
ADC_Keywords: Stars, brown dwarf ; Spectra, infrared
Keywords: instrumentation: spectrographs - methods: observational -
planets and satellites: atmospheres - stars: atmospheres -
brown dwarfs
Abstract:
Cold brown dwarf atmospheres provide a good training ground for the
analysis of atmospheres of temperate giant planets.
WISEP J173835.52+273258.9 (WISE 1738) is an isolated cold brown dwarf
and a Y0 spectral standard with a temperature between 350-400K, lying
at the boundary of the T-Y transition. Although its atmosphere has
been extensively studied in the near-infrared, its bulk physical
parameters and atmospheric chemistry and dynamics are not well
understood. Using a Mid-Infrared Instrument (MIRI) medium-resolution
spectrum (5-18um), combined with near-infrared spectra (0.98-2.2um)
from Hubble Space Telescope's (HST) Wide Field Camera 3 (WFC3) and
Gemini Observatory's Near-Infrared Spectrograph (GNIRS), we aim to
accurately characterize the atmospheric chemistry and bulk physical
parameters of WISE 1738. We perform a combined atmospheric retrieval
on the MIRI, GNIRS and WFC3 spectra using a machine learning algorithm
called Neural Posterior Estimation (NPE) assuming a cloud-free model
implemented using petitRADTRANS. We demonstrate how this combined
retrieval approach ensures robust constraints on the abundances of
major atmospheric species, the pressure-temperature (P-T) profile,
bulk C/O and metallicity [M/H], along with bulk physical properties
such as effective temperature, radius, surface gravity, mass and
luminosity. We estimate 1D and 2D marginal posterior distributions for
the constrained parameters and evaluate our results using several
qualitative and quantitative Bayesian diagnostics, including Local
Classifier 2-Sample Test (L-C2ST), coverage and posterior predictive
checks. The combined atmospheric retrieval confirms previous
constraints on H2O, CH4, NH3, and for the first time provides
constraints on CO, CO2 and 15NH3. It also gives better
constraints on the physical parameters and the P-T profile, while also
revealing potential biases in characterizing objects using data from
limited wavelength ranges. The retrievals further suggest the presence
of disequilibrium chemistry, as evidenced by the constrained
abundances of CO and CO2, which are otherwise expected to be depleted
and hence not visible beyond the near-infrared wavelengths under
equilibrium conditions. We estimate the physical parameters of the
object as follows: an effective temperature of 402+12-9K, surface
gravity (logg) of 4.43+0.26-0.34cm/s2, mass of
13+11-7M{Jup}, radius of 1.14+0.03-0.03R{Jup}, and a
bolometric luminosity of -6.52+0.05-0.04logL/L☉. Based on
these values, the evolutionary models suggest an age between 1 and
4Gyr, which is consistent with a high rotation rate of 6hr of the
brown dwarf. We further obtain an upper bound on the 15NH3
abundance, enabling a 3-sigma lower bound calculation of the
14N/15N ratio = 275, unable to interpret the formation pathway as
core collapse. Additionally, we calculate a C/O ratio of
1.35+0.39-0.31 and a metallicity of 0.34+0.12-0.11 without
considering any oxygen sequestration effects.
Description:
This dataset contains reduced and calibrated spectra of WISEP 1738,
produced with the JWST/MIRI medium-resolution spectrograph.
Objects:
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RA (2000) DE Designation(s)
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17 38 35.27 +27 33 02.3 WISEP J173835.52+273258.9 = CNS5 4359
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
spcmidi.dat 72 1298 MIRI/JWST spectrum of
WISEP J173835.52+273258.9 (5-18um)
spcmidi.fits 2880 21 fits version of MIRI/JWST spectrum of
WISEP J173835.52+273258.9
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Byte-by-byte Description of file: spcmidi.dat
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Bytes Format Units Label Explanations
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1- 19 F19.16 um lambda [4.9/17.97] Wavelength of each spectral bin
21- 49 E29.27 Jy Flux Flux density in Jansky
50- 72 E23.17 Jy e_Flux Uncertainty on flux in Jansky
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Acknowledgements:
Malavika Vasist, malavika.vasist47(at)gmail.com
(End) Patricia Vannier [CDS] 15-Sep-2025