characterizing atmospheres with jwst: optimizing multi-instrument observations via simulations and...
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![Page 1: Characterizing atmospheres with JWST: Optimizing multi-instrument observations via simulations and retrievals Tom Greene (NASA ARC) Michael Line (UCSC](https://reader036.vdocuments.net/reader036/viewer/2022070414/5697c00a1a28abf838cc7cf9/html5/thumbnails/1.jpg)
Characterizing atmospheres with JWST: Optimizing multi-instrument observations via
simulations and retrievals
Tom Greene (NASA ARC)Michael Line (UCSC / Hubble Fellow / ARC),
Jonathan Fortney (UCSC)November 16, 2015
Also see the posterBy Everett Schlawin
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3JWST Transit Characterization
Some progress from transit (spectroscopy)
16 Nov 2015
• Molecules & atoms identified in exoplanet atmospheres– H2O, CO (CH4, CO2), Na, other alkali, HI, CII, OI,…
• Measured temperature-pressure profiles from hot Jupiter emission spectra– Few with high confidence T inversions
• Some Neptune-sized planets have been diagnosed– HAT-P-11 (Fraine+ 2014) and GJ 436b (Knutson+, etc.)
• Sub-Neptunes and super-Earths have been difficult– GJ 1214b: flat absorption, no sec. eclipse (many people…)
– Promise of cooler planets like K2-3 (Crossfield+ 2015) and K2-18b (Montet+ 2015): T = 300 – 500K, different clouds?
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Questions about exoplanet atmospheres• What are their compositions?
– Elemental abundances • C/O and [Fe/H]: Both are formation diagnostics
– Molecular components and chemical processes• Identify equilibrium & disequilibrium chemistry:
– Vertical mixing, photochemistry, ion chemistry…
– 3-D effects: spatial variations• Energy budget and transport
– 1-D structure: measure profiles, inversions present?– Dynamical transport: day/night differences
• Clouds– Cloud composition, particle sizes, vertical & spatial distribution– Remove cloud effects to determine bulk properties
• Anything about low mass / small r< ~2Re planet atmospheres
• Trends with bulk parameters (mass, insolation, host stars, …)– Requires a population of diverse planets16 Nov 2015 JWST Transit Characterization 4
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5JWST Transit Characterization16 Nov 2015
We clearly can use all ~10 years of JWST time to observe transiting planets!
But what should we do if that doesn’t happen?
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6JWST Transit Characterization
New JWST Simulation / Retrieval Assessment
16 Nov 2015
Model some known planet types, simulate spectra, assess information & constraints
• Select archetypal planets from known system parameters– Hot Jupiter, warm Neptune, warm sub-Neptune, cool super-Earth
• Create model transmission and emission spectra (M. Line)
• Simulate JWST spectra using performance models (TG)– Simulate slitless modes with large bandpasses & good bright limits: NIRISS
SOSS, NIRCam grisms, MIRI LRS slitless 1 – 11 mm
– Code based on instrument models & data, detector parameters, JWST background models, random & systematic noise
– 1 transit or eclipse per spectrum
• Perform atmospheric retrievals (M. Line) to assess uncertainties in molecules, abundances, T-P profiles– Focus on uncertainties, not absolute parameters
• Identify what wavelengths give most useful information for what planets
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7JWST Transit Characterization
• Use 1-D forward models– Emission: Line+(2013a), Diamond-Lowe+(2014), Stevenson+(2014)– Transmission: Line+(2013b) Swain+(2014), Kreidberg+(2014, 2015)
• Transmission model has 11 free parameters– T(SH), R(P=10b),hard clouds (Pc, s0, b), H2O, CH4, CO, CO2, NH3, N2
absorbers, constant with altitude
• Emission model has 1D T-P profile & 10 free params– H2O, CH4, CO, CO2, NH3, 5 gray atm parameters for T-P (Line+ 2013a)
• CHIMERA Bayesian retrieval suite (Line+ 2013a,b)– Updated with emcee MCMC– Uniform & Jeffreys priors
16 Nov 2015
Forward models & retrievals
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Simulated Planet Signals (Sl) & Noise (Nl)
16 Nov 2015 8JWST Transit Characterization
l (mm) Noise floor
1.0 – 2.5 20 ppm
2.5 – 5.0 30 ppm
5.0 - 12 50 ppm
NIRISS
NIRCam
MIRI LRS
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Selected Model Systems
16 Nov 2015 9JWST Transit Characterization
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Model Transmission Spectra
16 Nov 2015 10JWST Transit Characterization
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Simulated JWST Trans Spectra (1 transit)
16 Nov 2015 11JWST Transit Characterization
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Model Emission Spectra
16 Nov 2015 12JWST Transit Characterization
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Simulated JWST Emission Spectra (1 eclipse)
16 Nov 2015 13JWST Transit Characterization
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Retrieval Birds & Bees
16 Nov 2015 14JWST Transit Characterization
Benneke & Seager (2012)
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Retrieval Results: Hot Jupiter Gasses
16 Nov 2015 15JWST Transit Characterization
Priors
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Retrieval Results: Warm Neptune Gasses
16 Nov 2015 16JWST Transit Characterization
Priors
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Retrieval: Warm Sub-Neptune Gasses
16 Nov 2015 17JWST Transit Characterization
Priors
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Retrieval Result: Cool Super-Earth Gasses
16 Nov 2015 18JWST Transit CharacterizationPriors
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Emission retrievals: T-P Profiles
16 Nov 2015 19JWST Transit Characterization
Dashed: True valueSolid line: Retrieved mean valueShaded: 1 sigma
Detect inversion at 4 sigma with NIRISS only (red)
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16 Nov 2015 20JWST Transit Characterization
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Mass - Metallicity
16 Nov 2015 22JWST Transit Characterization
Transmission spectra Adapted from Kreidberg+ 2014b
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JWST Transit Characterization 24
Summary / Conclusions (1)• NIRISS (1 – 2.5 mm) transmission spectra alone
sometimes constrain mixing ratios of dominant molecules in clear solar atmosphere planets (H2O, CH4, NH3)– C/O and [Fe/H] sometimes constrained with only NIRISS– l ≥ 5 mm spectra needed in a number of cases
• Cloudy solar atmospheres are often constrained (~ 1 dex or better mixing ratios) with l = 1 - 11 mm spectra – Transmission is better than emission for warm sub-Neptune– Hot Jupiter and warm Neptune do better with emission
• Need sufficient Fp and high Fp/F* for useful emission spectra
• High MMW atmospheres can be identified by high [Fe/H]• C/O is constrained to 0.2 dex for hot Jupiters with l = 1 –
5+ mm spectra. Also: C/O for hot planets with H2O + Teq• s[Fe/H] < 0.5 dex for warm, clear planets (l = 1-5+ mm tr)
16 Nov 2015
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JWST Transit Characterization 25
Summary / Conclusions (2)• Non-equilibrium vertical mixing cannot be detected via
molecular mixing ratios– Photochemistry could show unexpected spectral features
• Observing 5 planets from Uranus to Jupiter mass should measure [Fe/H] vs. Log (M) slope to 1s = 0.13– l = 1-5+ mm transmission spectra– More than adequate (~20s) for detecting Solar System slope
• These results are for observations of single transits or eclipses. We will not know the actual JWST data quality – and how noise will decrease with co-adding – until after launch
• Many more retrieval issues to be explored (binning, Bayesian estimators, priors, 3D, parameterization), but will largely be driven by future data16 Nov 2015
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JWST Transit Characterization 26
The End
16 Nov 2015