The Future of Ultracool Dwarf Science with JWST

Marley, Mark S.; Leggett, S. K.

doi:10.1007/978-1-4020-9457-6_4

Cited by 11 publications

(8 citation statements)

References 78 publications

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“…Integration of a spectral energy distribution consisting of a red optical and near-infrared spectrum, an L-band photometric point and/or WISE W1 and W2 points, and a Rayleigh Jeans tail to account for (unobserved) emergent flux at longer wavelengths therefore provides a reasonably accurate estimate of F bol (Cushing et al 2006;Filippazzo et al 2015). However the shift in the peak of the Planck function to longer wavelengths for the cooler late-type T dwarfs and Y dwarfs complicates the calculation of their bolometric fluxes because more and more energy emerges at wavelengths that are either difficult or impossible to access with current instrumentation (Marley & Leggett 2009).…”

Section: Bolometric Luminositymentioning

confidence: 99%

An Improved Near-infrared Spectrum of the Archetype Y Dwarf WISEP J182831.08+265037.8

Cushing¹,

Schneider

Kirkpatrick

et al. 2021

ApJ

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We present a Hubble Space Telescope/Wide-Field Camera 3 near-infrared spectrum of the archetype Y dwarf WISEP 182831.08+265037.8. The spectrum covers the 0.9-1.7 μm wavelength range at a resolving power of λ/ Δλ ≈ 180 and is a significant improvement over the previously published spectrum because it covers a broader wavelength range and is uncontaminated by light from a background star. The spectrum is unique for a cool brown dwarf in that the flux peaks in the Y, J, and H bands are of near equal intensity in units of f λ . We fail to detect any absorption bands of NH 3 in the spectrum, in contrast to the predictions of chemical equilibrium models, but tentatively identify CH 4 as the carrier of an unknown absorption feature centered at 1.015 μm. Using previously published ground-and spaced-based photometry, and using a Rayleigh-Jeans tail to account for flux emerging longward of 4.5 μm, we compute a bolometric luminosity of, which is significantly lower than previously published results. Finally, we compare the spectrum and photometry to two sets of atmospheric models and find that the best overall match to the observed properties of WISE 1828+2650 is a ∼1 Gyr old binary composed of two T eff ∼ 325 K, ∼5 M Jup brown dwarfs with subsolar [C/O] ratios.Unified Astronomy Thesaurus concepts: Near infrared astronomy (1093); Y dwarfs (1827); Spectroscopy (1558); Brown dwarfs (185)

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Section: Bolometric Luminositymentioning

confidence: 99%

An Improved Near-infrared Spectrum of the Archetype Y Dwarf WISEP J182831.08+265037.8

Cushing¹,

Schneider

Kirkpatrick

et al. 2021

ApJ

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“…JWST promises to revolutionize our knowledge of brown dwarf atmospheres due to: a vastly improved wavelength coverage across the near and mid infrared, combined with improved SNR and spectral resolution (Marley & Leggett 2009). Here we take a preliminary look at the potential improvement in our retrieval parameters with JWST for a representative T9 object (W0404).…”

Section: Jwst Simulation Constraintsmentioning

confidence: 99%

A Uniform Retrieval Analysis of Ultra-cool Dwarfs. III. Properties of Y Dwarfs

Zalesky

Line

Schneider

et al. 2019

ApJ

109

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Ultra-cool brown dwarfs offer a unique window into understanding substellar atmospheric physics and chemistry. Their strong molecular absorption bands at infrared wavelengths, Jupiter-like radii, cool temperatures, and lack of complicating stellar irradiation, make them ideal test-beds for understanding Jovian-like atmospheres. Here we report the findings of a uniform atmospheric retrieval analysis on a set of 14 Y and T-dwarfs observed with the Hubble Space Telescope Wide Field Camera 3 instrument. From our retrieval analysis, we find the temperature-structures to be largely consistent with radiative-convective equilibrium in most objects. We also determine the abundances of water, methane, and ammonia and upper limits on the alkali metals sodium and potassium. The constraints on water and methane are consistent with predictions from chemical equilibrium models, while those of ammonia may be affected by vertical disequilibrium mixing, consistent with previous works. Our key result stems from the constraints on the alkali metal abundances where we find their continued depletion with decreasing effective temperature, consistent with the trend identified in a previous retrieval analysis on a sample of slightly warmer late T-dwarfs in Line et al. (2017). These constraints show that the previously observed Y-J color trend across the T/Y transition is most likely due to the depletion of these metals in accordance with predictions from equilibrium condensate rainout chemistry. Finally, we simulate future James Webb Space Telescope observations of ultra-cool dwarfs and find that the NIRSpec PRISM offers the best chance at developing high-precision constraints on fundamental atmospheric characteristics.

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“…Infrared instruments on board of the James-Webb Space Telescope are expected to revolutionise our understanding of cool objects like exoplanets, brown dwarfs and cool stars (e.g. Marley & Leggett 2009;Beichman et al 2014). High-resolution ground-based spectroscopy with e.g.…”

Section: Introductionmentioning

confidence: 99%

Equilibrium chemistry down to 100 K

Woitke

Helling

Hunter

et al. 2018

A&A

234

241

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We introduce a fast and versatile computer code, GGchem, to determine the chemical composition of gases in thermo-chemical equilibrium down to 100 K, with or without equilibrium condensation. We review the data for molecular equilibrium constants, k p (T ), from several sources and discuss which functional fits are most suitable for low temperatures. We benchmark our results against another chemical equilibrium code. We collect Gibbs free energies, ∆G• − f , for about 200 solid and liquid species from the NIST-JANAF database and the geophysical database SUPCRTBL. We discuss the condensation sequence of the elements with solar abundances in phase equilibrium down to 100 K. Once the major magnesium silicates Mg 2 SiO 4 [s] and MgSiO 3 [s] have formed, the dust/gas mass ratio jumps to a value of about 0.0045 which is significantly lower than the often assumed value of 0.01. Silicate condensation is found to increase the carbon/oxygen ratio (C/O) in the gas from its solar value of ∼ 0.55 up to ∼ 0.71, and, by the additional intake of water and hydroxyl into the solid matrix, the formation of phyllosilicates at temperatures below ∼ 400 K increases the gaseous C/O further to about 0.83. Metallic tungsten (W) is the first condensate found to become thermodynamically stable around 1600 − 2200 K (depending on pressure), several hundreds of Kelvin before subsequent materials like zirconium dioxide (ZrO 2 ) or corundum (Al 2 O 3 ) can condense. We briefly discuss whether tungsten, despite its low abundance of ∼ 2 × 10 −7 times the silicon abundance, could provide the first seed particles for astrophysical dust formation. The GGchem code is publicly available at https://github.com/pw31/GGchem.

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The Future of Ultracool Dwarf Science with JWST

Cited by 11 publications

References 78 publications

An Improved Near-infrared Spectrum of the Archetype Y Dwarf WISEP J182831.08+265037.8

An Improved Near-infrared Spectrum of the Archetype Y Dwarf WISEP J182831.08+265037.8

A Uniform Retrieval Analysis of Ultra-cool Dwarfs. III. Properties of Y Dwarfs

Equilibrium chemistry down to 100 K

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