J/ApJ/953/170 FIRE MRS spectrum of the BD UGPSJ072227.51-054031.2 (Hood+, 2023)
Brown dwarf retrievals on FIRE!: atmospheric constraints and lessons learned
from high signal-to-noise medium-resolution spectroscopy of a T9 dwarf.
Hood C.E., Fortney J.J., Line M.R., Faherty J.K.
<Astrophys. J., 953, 170 (2023)>
=2023ApJ...953..170H 2023ApJ...953..170H
ADC_Keywords: Stars, brown dwarf; Stars, T-type; Spectra, infrared
Keywords: Brown dwarfs ; T dwarfs ; Atmospheric composition ;
Bayesian statistics
Abstract:
Brown dwarf spectra offer vital testbeds for our understanding of the
chemical and physical processes that sculpt substellar atmospheres.
Recently, atmospheric retrieval approaches have been successfully
applied to low-resolution (R∼100) spectra of L, T, and Y dwarfs,
yielding constraints on the chemical abundances and temperature
structures of these atmospheres. Medium-resolution (R∼103) spectra
of brown dwarfs offer additional insight, as molecular features are
more easily disentangled and the thermal structure of the upper
atmosphere is better probed. We present results from a GPU-based
retrieval analysis of a high signal-to-noise, medium-resolution
(R∼6000) FIRE spectrum from 0.85 to 2.5µm of the T9 dwarf
UGPS_J072227.51-054031.2. At 60x higher spectral resolution than
previous brown dwarf retrievals, a number of novel challenges arise.
We examine the effect of different opacity sources, in particular for
CH4. Furthermore, we find that flaws in the data like errors from
order stitching can bias our constraints. We compare these retrieval
results to those for an R∼100 spectrum of the same object, revealing
how constraints on atmospheric abundances and temperatures improve by
an order of magnitude or more with increased spectral resolution. In
particular, we can constrain the abundance of H2S, which is
undetectable at lower spectral resolution. While these
medium-resolution retrievals offer the potential of precise,
stellar-like constraints on atmospheric abundances (∼0.02dex), our
retrieved radius is unphysically small (R=0.50-0.01+0.01RJup),
indicating shortcomings with our modeling framework. This work is an
initial investigation into brown dwarf retrievals at medium spectral
resolution, offering guidance for future ground-based studies and JWST
observations.
Description:
We perform our analysis on the medium-resolution spectrum of
UGPS_J072227.51-054031.2 presented by Bochanski+ 2011AJ....142..169B 2011AJ....142..169B
obtained with the Folded-port InfraRed Echellette (FIRE) at the
Magellan Telescopes. This spectrum covers 0.85-2.5um over 21 orders
with R∼6000. We scaled the reduced and order-stitched spectrum of
B11 to the observed H-band photometry on the Maunakea Observatories
(MKO) photometric system.
We also use the low-resolution spectrum of UGPS 0722 from the SpeX
Prism Library (Burgasser 2014ASInC..11....7B 2014ASInC..11....7B), which covers a similar
wavelength range of 0.8-2.5um with a wavelength-dependent resolution
of ∼87-300. This spectrum was also calibrated to flux units using the
same H-band photometry as for the FIRE spectrum.
Objects:
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RA (ICRS) DE Designation(s)
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07 22 27.90 -05 40 33.5 GPS J0722 = UGPS J072227.51-054031.2
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
fig1.dat 49 26349 The FIRE spectrum of UGPS J072227.51-054031.2
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See also:
VI/133 : A variationally computed hot NH3 line list - BYTe (Yurchenko+, 2011)
J/other/ARA+A/43.195 : L and T dwarf stars (Kirkpatrick, 2005)
J/AJ/137/1 : PMs and astrometry of late-type dwarfs (Faherty+, 2009)
J/ApJ/752/56 : BDKP. III. Plxs for 70 ultracool dwarfs (Faherty+, 2012)
J/ApJS/214/25 : Rosseland & Planck gaseous mean opacities (Freedman+, 2014)
J/MNRAS/440/1649 : ExoMol line lists for CH4 (Yurchenko+, 2014)
J/A+A/589/A21 : K-H2 line shapes for cool BDs spectra (Allard+, 2016)
J/ApJS/225/10 : Kinematic analysis of M7-L8 dwarfs (Faherty+, 2016)
J/ApJ/856/23 : BANYAN. XI. The BANYAN Σ algorithm (Gagne+, 2018)
J/MNRAS/490/4638 : ExoMol molecular line lists. XXXV. NH3 (Coles+, 2019)
J/AJ/160/63 : IR sp. of 5 BDs with Gemini North IRS (Miles+, 2020)
J/ApJ/918/11 : IR photometry of late-type brown dwarfs (Leggett+, 2021)
J/ApJ/940/164 : Distance-calibrated SED of Gl 229B (Calamari+, 2022)
J/AJ/164/155 : K-band sp. of substellar companion VHS1256b (Hoch+, 2022)
Byte-by-byte Description of file: fig1.dat
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Bytes Format Units Label Explanations
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1- 7 F7.5 um lambda [0.8/2.5] Wavelength
9- 18 E10.3 W/m2/m OFlux [-5.3e-07/9.5e-07] Original flux (1)
20- 28 E9.3 W/m2/m e_OFlux [1e-23/8e-07] Uncertainty in OFlux (1)
30- 39 E10.3 W/m2/m NFlux [-2.4e-09/4.3e-09] New flux (2)
41- 49 E9.3 W/m2/m e_NFlux [4.4e-26/3.6e-09] Uncertainty in NFlux (2)
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Note (1): These are the flux values pre-photometric calibration
from Bochanski+ 2011AJ....142..169B 2011AJ....142..169B
Note (2): These values are scaled to the observed H-band photometry
on the Mauna Kea Observatories photometric system following
Line+ 2017ApJ...848...83L 2017ApJ...848...83L
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History:
From electronic version of the journal
Licences: cc-by
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 25-Sep-2025