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JPL-CITParis 2008 On NIR HST Spectro-photometry of Transiting Exo-planets Vasisht, Swain, Deroo, Chen, Wayne (JPL), Tinetti (UCL), Yung (CIT), Angerhausen (PIUK), Bouwman (MPIA), Deming (GSFC)
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Outline Motivation for NIR objective mode, time-resolved spectroscopy Instrumental issues > General issues confronting shot-noise limited spectroscopy > Hubble specific limitations Modeling and removal of instrumental limitations Spectroscopy of the emergent flux from HD189733b (Swain, Vasisht, Tinetti, Deroo, Yung et al., accepted ApJL) JPL-CITParis 2008
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Spectroscopy with NICMOS Slitless Grism spectrograph between 0.8- 2.5 microns Camera 3 –Coverage by 3 grisms located in filter wheel –R = 200 native spectral resolution –Camera 3 is severely under-sampled at 0.2”/pixel (~λ/D @ 2 um, 52” FOV) Exoplanet datasets have now been acquired with all grisms –G141 on HD 209548b (Brown et al. in 2005, unpublished) JPL-CITParis 2008
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Scientific Rationale NIR Emission Spectroscopy (λ ~1-2.5 um; Spitzer 3-30 um) –Observable: Falling but favorable flux contrast (< 3 um) –Energetically Important: Maximum νF ν (for emergent flux) –Decreased stellar shot-noise –NIR photosphere at greater pressure depths (0.1-1 bar) –Molecular activity: ro-vib bands of major species Again some of the same advantages apply for transmission spectroscopy –Reduced opacity from small particle scattering JPL-CITParis 2008
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Hot, Cold or Cloudy JPL-CITParis 2008 Seager et al. 2005 Homogenous clouds Hot T = 1750 K dayside reradiation
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Active (common) C,N,O molecules JPL-CITParis 2008 Lodders & Fegley 2002
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JPL-CITParis 2008 Hubeny & Burrows 2008
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Molecular spectroscopy -> atmospheric physics –Atmospheres are a window to planetary composition, may have clues to evolutionary history –History of the planet can give rise to a range in core sizes, heavy element abundances, and abundance ratios –Relative fractions of refractory and volatile materials should reflect upon Parent star abundances, history of formation, migration (?) JPL-CITParis 2008
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JPL-CITParis 2008 Part II – Photometry with HST 1.Detector anomalies 2.Optical anomalies Photometric systematic noise
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JPL-CITParis 2008 NICMOS Detector Effects Stress induced structure in the response Pixel-to-Pixel stochastic response variations Intrapixel structure in the response T-dependence Figer et al. 2002
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Large scale structure JPL-CITParis 2008 NIC-3 is under- sampled PAM Defocus provides some “Immunity” This sets R ~ 40 Watch for structure under spectrum. Flats can remove some of this power
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JPL-CITParis 2008 Small-scale structure and MTF Finger et al. 2000Stiavelli et al.
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JPL-CITParis 2008 Relative Photometry Evaluate in some statistical fashion
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JPL-CITParis 2008 Relative Photometry k-space Variance is integral over spatial frequencies of –Power spectrum of the detector response apodised by 1. Power spectrum of the illumination 2. 1-cos() high pass filter
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14/08/2008Paris 2008 1-cos(k dx), dx = 0.1 pix Intrapixel gainPSF Defocused PSF by Ray Tracing: Note this is a PSD Diffraction
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Implications Significant substructure in the psf (ILS) –At spatial frequencies of D/λ, D/2λ etc –Due to diffraction –D/λ ~ 1/pixel –Mostly preserved in cross-dispersion axis Varies with wavelength –For shorter λ, higher spatial frequencies Can interact with sub-pixel structure JPL-CITParis 2008
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Beam wander In x (spatial) and y (spectral) Repositioning errors –Filter wheel positioning –Rot. about un-deviated ray Orbital phase PSF modulation –Proxy (Gaussian FWHM) Array response variations – QE with temperature –~ 1%/K (2.5 micron), 3%/K (1.5 micron) JPL-CITParis 2008 DISCRETE OFFSETS X, Y, θ, T PERIODIC σ
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Biggest headache is image motion Repositioning errors (Monte Carlo) –δx, δy ~ 0.1 pixel; linear perturbations –δx, δy > 0.25 pixels; large higher order errors (> 10 -4 ) Generally few usable orbits per visit –Adding 2 nd order terms to expansion is problematic JPL-CITParis 2008 dx, dy, dθ dT Σ dσ dI
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JPL-CITParis 2008
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JPL-CITParis 2008
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JPL-CITParis 2008 Orbit 1
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JPL-CITParis 2008 Other Systematics Optical effects –Flux-migration between grating-orders Response of interference filter Geometrical shadowing by grooves Woods anomalies
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JPL-CITParis 2008 Part III – Observations of HD 189733b Part III – Observations of HD 189733b
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State-Variables HD189733b Paris 2008 angle temperature defocus position
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Iterative Multivariate Fits JPL-CIT Light curve Design Matrix Model vector Noise
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JPL-CITParis 2008 Data Modeling-III Raw periodogram Post-fit residuals
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Lightcurves JPL-CITParis 2008 Broadband 1.5 To 2.5 um K band K band with Common mode Noise removed Final K band Lightcurve
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HD 189733 (Basic Data) HD 189733 (K1-K2V) –T ~ 5000 K –19.3 pc –> 0.6 Gyr –Metallicity -0.03 +/- 0.04 HD 189733b (Bouchy et al. 2005) –1.144 MJ, 1.138 RJ –Circular 0.03 AU orbit (2.22 d) Secondary eclipse observations –Barnes et al. 2007 (dC ~ 4x10 -4 ) JPL-CITParis 2008 J. Schneider, Ex. Enc.
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Spectral Modeling Retrieval using RT models (Goody & Yung 1989) Disk-averaged radiative transfer models developed originally for Earthshine, Mars (Tinetti et al. 2006, 2007) P-T profiles (Barman et al. 2008, Burrows et al. 2008) Photochemistry (Yung, Liang) Layer-by-layer (log P between -6 and 0) –Input T-P profiles –Chemical profiles (simple constant VMR) –Opacities (T, ρ); Cloudless. JPL-CITParis 2008
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JPL-CITParis 2008 HD189733b NIR Contrast Spectrum
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14/08/2008 Contrast Spectrum Components
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Paris 2008 Showman et al. 2008Comparison with radiation-hydrodynamics models Planet brightest away from anti-stellar point Knutson et al. 2007
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JPL-CITParis 2008 Retrieval Results Dayside emission (subsolar) –Water (0.1-1 10 -4 ) –Carbon monoxide (thermochemically very stable at these P,Ts; CO=CH4 T=1100K at 1 bar) Also inferred from IRAC photometry (Charbonneau et al. 2008) 10 -4 –Carbon dioxide (trace concentration 10 -6 ) CO+H2O CO2+H2 (thermochemical in a CO field; Lodders & Fegley 2002) CO+OH CO2+H (photochemical pathway) –Methane upper limit (10 -7 ) –Significant residuals at the blue end of the spectrum
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JPL-CITParis 2008 Abundances C/O is high and not well constrained (cloudless model) –0.5 to 10 Solar 0.48 (Anders & Grevesse 1989) Favor lower values because high C/O implies disappearing water in CO field –Terminator (Swain, Vasisht, Tinetti 2008) Lower pressure depths Methane abundance is higher (CO < CH4) Water 5.10 -4
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In Summary JPL-CITParis 2008 Little evidence for … Hot Jovians not as “hot” as … good hot Curry !.
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Chemistry Hot less dense atmospheres are more likely to show abundant CO (and CO2 at lower T), while cooler, denser ones show more abundant methane. At 1 bar the CO=CH4 boundary is at T = 1125 K. C/O atomic ratio is 0.48 (solar) 14/08/2008Exeter Exoplanet Workshop
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JPL-CITParis 2008
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JPL-CITParis 2008 Pont et al. 2008
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JPL-CITParis 2008 F. Pont et al. 2008
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Carbon & Oxygen Chemistry Major carbon bearing gases in a solar composition gas of given metallicity are generally CH4, CO and/or CO2 depending on T and P. 14/08/2008Exeter Exoplanet Workshop
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