The Sonora Substellar Atmosphere Models. II. Cholla: A Grid of Cloud-free, Solar Metallicity Models in Chemical Disequilibrium for the JWST Era

Abstract Exoplanet and brown dwarf atmospheres commonly show signs of disequilibrium chemistry. In the James Webb Space Telescope (JWST) era, high-resolution spectra of directly imaged exoplanets will allow the characterization of their atmospheres in more detail, and allow systematic tests for the presence of chemical species that deviate from thermochemical equilibrium in these atmospheres. Constraining the presence of disequilibrium chemistry in these atmospheres as a function of parameters such as their effective temperature and surface gravity will allow us to place better constraints on the physics governing these atmospheres. This paper is part of a series of works presenting the Sonora grid of atmosphere models. In this paper, we present a grid of cloud-free, solar metallicity atmospheres for brown dwarfs and wide-separation giant planets with key molecular species such as CH4, H2O, CO, and NH3 in disequilibrium. Our grid covers atmospheres with T eff ∈ [500 K, 1300 K], log g ∈ [3.0, 5.5] (cgs) and an eddy diffusion parameter of log K zz = 2 , 4 and 7 (cgs). We study the effect of different parameters within the grid on the temperature and composition profiles of our atmospheres. We discuss their effect on the near-infrared colors of our model atmospheres and the detectability of CH4, H2O, CO, and NH3 using the JWST. We compare our models against existing MKO and Spitzer observations of brown dwarfs and verify the importance of disequilibrium chemistry for T dwarf atmospheres. Finally, we discuss how our models can help constrain the vertical structure and chemical composition of these atmospheres.

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Bayesian Spectroscopic Characterization of Directly Imaged Planets and Brown Dwarfs and Implications for Ultracool Model Atmospheres

10.5194/epsc2021-818 ◽

2021 ◽

Author(s):

Zhoujian Zhang ◽

Michael Liu ◽

Mark Marley ◽

Michael Line ◽

William Best

Keyword(s):

Physical Properties ◽

Near Infrared ◽

Brown Dwarfs ◽

Spectroscopic Characterization ◽

Cool Temperature ◽

Brown Dwarf ◽

Modeling Framework ◽

High Quality ◽

Model Predictions

Spectroscopic characterization of imaged exoplanets and brown dwarfs is essential for understanding their atmospheres, formation, and evolution, but such work is challenged by the unavoidably simplified model atmospheres needed to interpret spectra. While most previous work has focused on single or at most a few objects, comparing a large collection of spectra to models can uncover trends in data-model inconsistencies needed to improve model predictions, thereby leading to robust properties from exoplanet and brown dwarf spectra. Therefore, we are conducting a systematic analysis of a valuable but underutilized resource: the numerous high-quality spectra of (directly imaged and free-floating) exoplanets and brown dwarfs already accumulated by the community.&#160; Focusing on the cool-temperature end, we have constructed a Bayesian modeling framework using the new Sonora-Bobcat model atmospheres and have applied it to study near-infrared low-resolution spectra of >50 late-T imaged planets and brown dwarfs (&#8776;600-1200K, &#8776;10-70 MJup) and infer their physical properties (effective temperature, surface gravity, metallicity, radii, mass). By virtue of having such a large sample of high-quality spectra, our analysis identifies the systematic offsets between observed and model spectra as a function of wavelength and physical properties to pinpoint specific shortcomings in model predictions. We have also found that the spectroscopically inferred metallicities, ages, and masses of our sample all considerably deviate from expectations, suggesting the physical and chemical assumptions made within these models need to be improved to fully interpret data. Our work has established a systematic validation of cloudless model atmospheres to date and we discuss extending such analysis to wider temperature and wavelength (e.g., JWST) ranges, as well as finding new planetary-mass and brown dwarf benchmarks, in order to validate ultracool model atmospheres over larger parameter space.

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AKARI near-infrared spectroscopy of brown dwarfs

Proceedings of the International Astronomical Union ◽

10.1017/s1743921310010641 ◽

2009 ◽

Vol 5 (H15) ◽

pp. 545-545

Author(s):

Issei Yamamura ◽

Takashi Tsuji ◽

Toshihiko Tanabé ◽

Tadashi Nakajima

Keyword(s):

Infrared Spectroscopy ◽

Low Temperature ◽

Near Infrared Spectroscopy ◽

Near Infrared ◽

Infrared Camera ◽

Brown Dwarfs ◽

Giant Planets ◽

Dust Clouds ◽

Molecular Abundances ◽

Observation Programme

Brown dwarfs (hereafter BDs) are of particular interest because of their extremely low-temperature atmospheres for comparison with atmospheres of giant planets. Aiming to obtain clues to understand the formation and disappearance of dust clouds and molecular abundances in BD photospheres, we conducted an observation programme of space-borne near-infrared spectroscopy of bright BDs with the Infrared Camera (IRC) on-board AKARI.

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A new set of atmosphere and evolution models for cool T–Y brown dwarfs and giant exoplanets

Astronomy and Astrophysics ◽

10.1051/0004-6361/201937381 ◽

2020 ◽

Vol 637 ◽

pp. A38 ◽

Cited By ~ 7

Author(s):

M. W. Phillips ◽

P. Tremblin ◽

I. Baraffe ◽

G. Chabrier ◽

N. F. Allard ◽

...

Keyword(s):

Near Infrared ◽

Vertical Mixing ◽

Emission Spectra ◽

Brown Dwarfs ◽

Atmospheric Temperature ◽

Temperature Structure ◽

Surface Boundary ◽

Quantum Molecular Dynamics ◽

Solar Metallicity ◽

The Impact

We present a new set of solar metallicity atmosphere and evolutionary models for very cool brown dwarfs and self-luminous giant exoplanets, which we term ATMO 2020. Atmosphere models are generated with our state-of-the-art 1D radiative-convective equilibrium code ATMO, and are used as surface boundary conditions to calculate the interior structure and evolution of 0.001–0.075 M⊙ objects. Our models include several key improvements to the input physics used in previous models available in the literature. Most notably, the use of a new H–He equation of state including ab initio quantum molecular dynamics calculations has raised the mass by ~1−2% at the stellar–substellar boundary and has altered the cooling tracks around the hydrogen and deuterium burning minimum masses. A second key improvement concerns updated molecular opacities in our atmosphere model ATMO, which now contains significantly more line transitions required to accurately capture the opacity in these hot atmospheres. This leads to warmer atmospheric temperature structures, further changing the cooling curves and predicted emission spectra of substellar objects. We present significant improvement for the treatment of the collisionally broadened potassium resonance doublet, and highlight the importance of these lines in shaping the red-optical and near-infrared spectrum of brown dwarfs. We generate three different grids of model simulations, one using equilibrium chemistry and two using non-equilibrium chemistry due to vertical mixing, all three computed self-consistently with the pressure-temperature structure of the atmosphere. We show the impact of vertical mixing on emission spectra and in colour-magnitude diagrams, highlighting how the 3.5−5.5 μm flux window can be used to calibrate vertical mixing in cool T–Y spectral type objects.

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Colour–colour and colour–magnitude diagrams for hot Jupiters

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1074 ◽

2020 ◽

Vol 494 (4) ◽

pp. 4939-4949 ◽

Cited By ~ 3

Author(s):

G Melville ◽

L Kedziora-Chudczer ◽

J Bailey

Keyword(s):

Measurement Errors ◽

Near Infrared ◽

Emission Spectra ◽

Brown Dwarfs ◽

Low Gravity ◽

Hot Jupiters ◽

Substellar Objects ◽

Solar Metallicity ◽

Ir Bands ◽

Individual Objects

ABSTRACT We use ground-based and space-based eclipse measurements for the near-infrared (IR) bands (JHKs) and Spitzer 3.6- and 4.5-μm bands to construct colour–colour and colour–magnitude diagrams for hot Jupiters. We compare the results with previous observations of substellar objects and find that hot Jupiters, when corrected for their inflated radii, lie near the blackbody line and in the same region of the colour–magnitude diagrams as brown dwarfs, including low-gravity dwarfs that have been previously suggested as exoplanet analogues. We use theoretical emission spectra to investigate the effects of different metallicity, C/O ratios, and temperatures on the IR colours. In general, we find that while differences in C/O ratio and metallicity do correspond to different locations on these diagrams, the measurement errors are too large to use this method to put strong constraints on the composition of individual objects. However, as a class, hot Jupiters cluster around the location expected for solar metallicity and C/O ratio.

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Ground-based exoplanet near-infrared search by imaging and spectroscopy: 3 new companion candidates in TWA

Symposium - International Astronomical Union ◽

10.1017/s0074180900218512 ◽

2004 ◽

Vol 202 ◽

pp. 465-467

Author(s):

Ralph Neuhäuser ◽

Nuria Huélamo ◽

Eike W. Guenther ◽

Wolfgang Brandner ◽

João Alves ◽

...

Keyword(s):

Near Infrared ◽

Infrared Imaging ◽

Brown Dwarfs ◽

T Tauri Stars ◽

Giant Planets ◽

T Tauri ◽

First Results ◽

Imaging And Spectroscopy ◽

Central Stars

We report first results from our ground-based infrared imaging search for sub-stellar companions (brown dwarfs and giant planets) of young (up to 100 Myrs) nearby (up to 100 pc) stars, where companions should be well separated from the central stars and still relatively bright due to ongoing accretion and/or contraction. Our observations are performed mainly with SOFI and SHARP at the ESO 3.5m NTT on La Silla (imaging) and with ISAAC at the ESO 8.2m Antu (VLT-UT1) on Cerro Paranal (imaging and spectroscopy), all in the H- and K-bands. Here, we present new companion candidates1 around three T Tauri stars (TWA-8 A, RXJ1121.1-3845, and RXJ1121.3-3447 N) in the TW Hya group, which would have been sub-stellar if at the same distance and age as the T Tauri stars, but are found to be background stars by spectroscopy.

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Characterization of the detector subsystem for near-infrared spectrograph (NIRSpec) on the James Webb Space Telescope

10.1117/12.734579 ◽

2007 ◽

Cited By ~ 2

Author(s):

D. Brent Mott ◽

Augustyn Waczynski ◽

Yiting Wen ◽

Wei Xia-Serafino ◽

Bernard J. Rauscher ◽

...

Keyword(s):

Near Infrared ◽

Space Telescope ◽

James Webb Space Telescope

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Ground-based follow-up observations of TRAPPIST-1 transits in the near-infrared

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz1375 ◽

2019 ◽

Vol 487 (2) ◽

pp. 1634-1652 ◽

Cited By ~ 4

Author(s):

A Y Burdanov ◽

S M Lederer ◽

M Gillon ◽

L Delrez ◽

E Ducrot ◽

...

Keyword(s):

Near Infrared ◽

Temporal Variations ◽

Transmission Spectra ◽

Data Set ◽

Near Ir ◽

James Webb Space Telescope ◽

Bright Spots ◽

Means Of Transmission

Abstract The TRAPPIST-1 planetary system is a favourable target for the atmospheric characterization of temperate earth-sized exoplanets by means of transmission spectroscopy with the forthcoming James Webb Space Telescope (JWST). A possible obstacle to this technique could come from the photospheric heterogeneity of the host star that could affect planetary signatures in the transit transmission spectra. To constrain further this possibility, we gathered an extensive photometric data set of 25 TRAPPIST-1 transits observed in the near-IR J band (1.2 μm) with the UKIRT and the AAT, and in the NB2090 band (2.1 μm) with the VLT during the period 2015–18. In our analysis of these data, we used a special strategy aiming to ensure uniformity in our measurements and robustness in our conclusions. We reach a photometric precision of 0.003 (RMS of the residuals), and we detect no significant temporal variations of transit depths of TRAPPIST-1 b, c, e, and g over the period of 3 yr. The few transit depths measured for planets d and f hint towards some level of variability, but more measurements will be required for confirmation. Our depth measurements for planets b and c disagree with the stellar contamination spectra originating from the possible existence of bright spots of temperature 4500 K. We report updated transmission spectra for the six inner planets of the system which are globally flat for planets b and g and some structures are seen for planets c, d, e, and f.

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Characterization of the detector subsystem for the near-infrared spectrograph (NIRSpec) on the James Webb Space Telescope

10.1117/12.789099 ◽

2008 ◽

Cited By ~ 2

Author(s):

D. Brent Mott ◽

Augustyn Waczynski ◽

Yiting Wen ◽

Bernard J. Rauscher ◽

Nicholas Boehm ◽

...

Keyword(s):

Near Infrared ◽

Space Telescope ◽

James Webb Space Telescope

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Unveiling shrouded oceans on temperate sub-Neptunes via transit signatures of solubility equilibria vs. gas thermochemistry

10.21203/rs.3.rs-481864/v1 ◽

2021 ◽

Author(s):

Renyu Hu ◽

Mario Damiano ◽

Markus Scheucher ◽

Edwin Kite ◽

Sara Seager ◽

...

Keyword(s):

Liquid Water ◽

Distinctive Features ◽

Carbon And Nitrogen ◽

Moderate Number ◽

James Webb Space Telescope ◽

Initial Characterization ◽

Thermochemical Equilibrium ◽

Near Term ◽

Atmospheric Mass

Abstract The recent discovery and initial characterization of sub-Neptune-sized exoplanets that receive stellar irradiance of approximately Earth's raised the prospect of finding habitable planets in the coming decade. Some of these temperate planets may support liquid water oceans, if they do not have massive H2/He envelopes and are thus not too hot at the bottom of the envelopes. For planets larger than Earth, and especially planets in the 1.7-3.5 R_Earth population, the mass of the H2/He envelope is typically not sufficiently constrained to assess the potential habitability. Here we show that the solubility equilibria vs. thermochemistry of carbon and nitrogen gases results in observable discriminators between small H2 atmospheres vs. massive ones. On temperate sub-Neptunes, the condition to form a liquid-water ocean and that to achieve the thermochemical equilibrium are mutually exclusive. The dominant carbon and nitrogen gases are typically CH4 and NH3 due to thermochemical recycling in a massive atmosphere of a temperate planet, and those in a small atmosphere overlying a liquid-water ocean are most likely CO2 and N2, followed by CO and CH4 produced photochemically. NH3 is depleted in the small atmosphere by dissolution into the liquid-water ocean. These gases lead to distinctive features in the planet's transmission spectrum, and a moderate number of repeated transit observations with the James Webb Space Telescope should readily tell apart a small atmosphere vs. a massive one via these spectral features on planets like K2-18 b. This method thus provides a way to use near-term facilities to constrain the atmospheric mass and habitability of temperate sub-Neptune exoplanets.

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Exploring the diversity of Jupiter-class planets

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rsta.2013.0064 ◽

2014 ◽

Vol 372 (2014) ◽

pp. 20130064 ◽

Cited By ~ 3

Author(s):

Leigh N. Fletcher ◽

Patrick G. J. Irwin ◽

Joanna K. Barstow ◽

Remco J. de Kok ◽

Jae-Min Lee ◽

...

Keyword(s):

Solar System ◽

Early Stage ◽

Vertical Mixing ◽

Spectroscopic Characterization ◽

Temperature Inversion ◽

Giant Planets ◽

Cloud Properties ◽

Thermochemical Equilibrium ◽

Physical And Chemical

Of the 900+ confirmed exoplanets discovered since 1995 for which we have constraints on their mass (i.e. not including Kepler candidates), 75% have masses larger than Saturn (0.3 M J ), 53% are more massive than Jupiter and 67% are within 1 AU of their host stars. When Kepler candidates are included, Neptune-sized giant planets could form the majority of the planetary population. And yet the term ‘hot Jupiter’ fails to account for the incredible diversity of this class of astrophysical object, which exists on a continuum of giant planets from the cool jovians of our own Solar System to the highly irradiated, tidally locked hot roasters. We review theoretical expectations for the temperatures, molecular composition and cloud properties of hydrogen-dominated Jupiter-class objects under a variety of different conditions. We discuss the classification schemes for these Jupiter-class planets proposed to date, including the implications for our own Solar System giant planets and the pitfalls associated with compositional classification at this early stage of exoplanetary spectroscopy. We discuss the range of planetary types described by previous authors, accounting for (i) thermochemical equilibrium expectations for cloud condensation and favoured chemical stability fields; (ii) the metallicity and formation mechanism for these giant planets; (iii) the importance of optical absorbers for energy partitioning and the generation of a temperature inversion; (iv) the favoured photochemical pathways and expectations for minor species (e.g. saturated hydrocarbons and nitriles); (v) the unexpected presence of molecules owing to vertical mixing of species above their quench levels; and (vi) methods for energy and material redistribution throughout the atmosphere (e.g. away from the highly irradiated daysides of close-in giants). Finally, we discuss the benefits and potential flaws of retrieval techniques for establishing a family of atmospheric solutions that reproduce the available data, and the requirements for future spectroscopic characterization of a set of Jupiter-class objects to test our physical and chemical understanding of these planets.

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