on nir hst spectro-photometry of transiting exo-planets

JPL-CITJPL-CIT Paris 2008Paris 2008

On NIR HST Spectro-photometry of On NIR HST Spectro-photometry of Transiting Exo-planets Transiting Exo-planets

Vasisht, Swain, Deroo, Chen, Wayne (JPL), Tinetti Vasisht, Swain, Deroo, Chen, Wayne (JPL), Tinetti (UCL), Yung (CIT), Angerhausen (PIUK), Bouwman (UCL), Yung (CIT), Angerhausen (PIUK), Bouwman

(MPIA), Deming (GSFC)(MPIA), Deming (GSFC)

OutlineOutline

Motivation for NIR objective mode, time-resolved Motivation for NIR objective mode, time-resolved spectroscopyspectroscopy

Instrumental issuesInstrumental issues> General issues confronting shot-noise limited spectroscopy> General issues confronting shot-noise limited spectroscopy

> Hubble specific limitations> Hubble specific limitations

Modeling and removal of instrumental limitationsModeling and removal of instrumental limitations Spectroscopy of the emergent flux from HD189733b Spectroscopy of the emergent flux from HD189733b

(Swain, Vasisht, Tinetti, Deroo, Yung et al., accepted (Swain, Vasisht, Tinetti, Deroo, Yung et al., accepted ApJL)ApJL)


Spectroscopy with NICMOSSpectroscopy with NICMOS


Scientific RationaleScientific Rationale

NIR Emission Spectroscopy (λ ~1-2.5 um; Spitzer 3-30 um)NIR Emission Spectroscopy (λ ~1-2.5 um; Spitzer 3-30 um)– Observable: Falling but favorable flux contrast (< 3 um)Observable: Falling but favorable flux contrast (< 3 um)

– Energetically Important: Maximum νFEnergetically Important: Maximum νFνν (for emergent flux) (for emergent flux)

– Decreased stellar shot-noiseDecreased stellar shot-noise– NIR photosphere at greater pressure depths (0.1-1 bar)NIR photosphere at greater pressure depths (0.1-1 bar)– Molecular activity: ro-vib bands of major speciesMolecular activity: ro-vib bands of major species

Again some of the same advantages apply for transmission Again some of the same advantages apply for transmission spectroscopyspectroscopy– Reduced opacity from small particle scattering Reduced opacity from small particle scattering


Hot, Cold or CloudyHot, Cold or Cloudy


Seager et al. 2005

Homogenous clouds

Hot T = 1750 K dayside reradiation

Active (common) C,N,O moleculesActive (common) C,N,O molecules


Lodders & Fegley 2002


Hubeny & Burrows 2008

Molecular spectroscopy -> atmospheric physicsMolecular spectroscopy -> atmospheric physics– Atmospheres are a window to planetary Atmospheres are a window to planetary

composition, may have clues to evolutionary composition, may have clues to evolutionary historyhistory

– History of the planet can give rise to a range in History of the planet can give rise to a range in core sizes, heavy element abundances, and core sizes, heavy element abundances, and abundance ratiosabundance ratios

– Relative fractions of refractory and volatile Relative fractions of refractory and volatile materials should reflect uponmaterials should reflect upon Parent star abundances, history of formation, migration Parent star abundances, history of formation, migration

(?) (?)



Part II – Photometry with HST

1. Detector anomalies2. Optical anomalies Photometric systematic noise


NICMOS Detector EffectsNICMOS Detector Effects

Stress induced Stress induced structure in the structure in the responseresponse

Pixel-to-Pixel stochastic Pixel-to-Pixel stochastic response variationsresponse variations

Intrapixel structure in Intrapixel structure in the responsethe response

T-dependenceT-dependence

Figer et al. 2002

Large scale structure Large scale structure


NIC-3 is under-sampled

PAM Defocus provides some“Immunity”

This setsR ~ 40

Watch for structure under spectrum. Flats can remove some of this power


Small-scale structure and MTFSmall-scale structure and MTF

Finger et al. 2000 Stiavelli et al.


Relative PhotometryRelative Photometry

€

I = dxdy psf (x, y) R(x, y)x,y

∫∫

I ' = dxdy psf (x + ∂x, y + ∂y)R(x, y)x,y

∫∫

ε 2 = (I ' − I)2Evaluate in some statistical fashion


Relative Photometry k-spaceRelative Photometry k-space

Variance is integral over spatial frequencies ofVariance is integral over spatial frequencies of– Power spectrum of the detector response Power spectrum of the detector response

apodised byapodised by 1. Power spectrum of the illumination1. Power spectrum of the illumination 2. 1-cos() high pass filter2. 1-cos() high pass filter

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ε2 = 2 d2kℑkx ,ky

∫∫r k ( )

2ℜ

r k ( )

21− cos(

r k ⋅Δ

r x )( )

14/08/200814/08/2008 Paris 2008Paris 2008

1-cos(k dx), dx = 0.1 pix

Intrapixel gainPSF

Defocused PSF by Ray Tracing: Note this is a PSD

Diffraction

ImplicationsImplications

Significant substructure in the psf (ILS)Significant substructure in the psf (ILS)– At spatial frequencies of D/λ, D/2λ etcAt spatial frequencies of D/λ, D/2λ etc– Due to diffractionDue to diffraction– D/λ ~ 1/pixelD/λ ~ 1/pixel– Mostly preserved in cross-dispersion axisMostly preserved in cross-dispersion axis

Varies with wavelengthVaries with wavelength– For shorter λ, higher spatial frequenciesFor shorter λ, higher spatial frequencies

Can interact with sub-pixel structureCan interact with sub-pixel structure


Beam wanderBeam wander In x (spatial) and y (spectral)In x (spatial) and y (spectral) Repositioning errorsRepositioning errors

– Filter wheel positioningFilter wheel positioning– Rot. about un-deviated rayRot. about un-deviated ray

Orbital phase PSF modulationOrbital phase PSF modulation– Proxy (Gaussian FWHM)Proxy (Gaussian FWHM)

Array response variationsArray response variations– QE with temperatureQE with temperature– ~ 1%/K (2.5 micron), 3%/K (1.5 micron)~ 1%/K (2.5 micron), 3%/K (1.5 micron)


DISCRETE OFFSETS X, Y, θ, TPERIODICσ

Biggest headache is image motionBiggest headache is image motion Repositioning errors (Monte Carlo)Repositioning errors (Monte Carlo)

– δx, δy ~ 0.1 pixel; linear perturbations δx, δy ~ 0.1 pixel; linear perturbations – δx, δy > 0.25 pixels; large higher order errors (> 10δx, δy > 0.25 pixels; large higher order errors (> 10--

44)) Generally few usable orbits per visitGenerally few usable orbits per visit

– Adding 2Adding 2ndnd order terms to expansion is problematic order terms to expansion is problematic


dx, dy, dθdx, dy, dθ

dTdT

Σ

dσdσ

dIdI


Orbit 1


Other SystematicsOther Systematics

Optical effectsOptical effects– Flux-migration between grating-ordersFlux-migration between grating-orders

Response of interference filterResponse of interference filter Geometrical shadowing by groovesGeometrical shadowing by grooves Woods anomaliesWoods anomalies


Part III – Observations of HD 189733bPart III – Observations of HD 189733b

State-Variables HD189733bState-Variables HD189733b

Paris 2008Paris 2008

angle

temperature

defocus

position

Iterative Multivariate FitsIterative Multivariate Fits

JPL-CITJPL-CIT

€

y1 − c1

y2 − c2

y3 − c3

M

yn − cn

⎡

⎣

⎢ ⎢ ⎢ ⎢ ⎢ ⎢

⎤

⎦

⎥ ⎥ ⎥ ⎥ ⎥ ⎥

= [∂r σ ∂

r x ∂

r y ∂

r θ

r φ ]

β

β x

β y

βθ

βφ

⎡

⎣

⎢ ⎢ ⎢ ⎢ ⎢ ⎢

⎤

⎦

⎥ ⎥ ⎥ ⎥ ⎥ ⎥

+

v1

v2

v3

M

vn

⎡

⎣

⎢ ⎢ ⎢ ⎢ ⎢ ⎢

⎤

⎦

⎥ ⎥ ⎥ ⎥ ⎥ ⎥

€

Y − C =HB + V

B=(HT H)−1HT (Y − C)

Light curve

Design Matrix

Model vector

Noise


Data Modeling-IIIData Modeling-IIIRaw periodogram

Post-fit residuals

LightcurvesLightcurves


Broadband 1.5To 2.5 um

K band

K band with Common modeNoise removed

Final K band Lightcurve

HD 189733 (Basic Data)HD 189733 (Basic Data)

HD 189733 (K1-K2V)HD 189733 (K1-K2V)– T ~ 5000 KT ~ 5000 K– 19.3 pc19.3 pc– > 0.6 Gyr> 0.6 Gyr– Metallicity -0.03 +/- 0.04Metallicity -0.03 +/- 0.04

HD 189733b (Bouchy et al. 2005)HD 189733b (Bouchy et al. 2005)– 1.144 MJ, 1.138 RJ1.144 MJ, 1.138 RJ– Circular 0.03 AU orbit (2.22 d)Circular 0.03 AU orbit (2.22 d)

Secondary eclipse observationsSecondary eclipse observations– Barnes et al. 2007 (dC ~ 4x10Barnes et al. 2007 (dC ~ 4x10-4-4))


J. Schneider, Ex. Enc.

Spectral ModelingSpectral Modeling

Retrieval using RT models (Goody & Yung 1989) Retrieval using RT models (Goody & Yung 1989) Disk-averaged radiative transfer models developed Disk-averaged radiative transfer models developed

originally for Earthshine, Marsoriginally for Earthshine, Mars (Tinetti et al. 2006, 2007)(Tinetti et al. 2006, 2007) P-T profiles (Barman et al. 2008, Burrows et al. 2008)P-T profiles (Barman et al. 2008, Burrows et al. 2008)

Photochemistry (Yung, Liang)Photochemistry (Yung, Liang) Layer-by-layer (log P between -6 and 0)Layer-by-layer (log P between -6 and 0)

– Input T-P profilesInput T-P profiles– Chemical profiles (simple constant VMR)Chemical profiles (simple constant VMR)– Opacities (T, ρ); Cloudless.Opacities (T, ρ); Cloudless.



HD189733b NIR Contrast SpectrumHD189733b NIR Contrast Spectrum

14/08/200814/08/2008

Contrast Spectrum Components Contrast Spectrum Components

Paris 2008Paris 2008

Showman et al. 2008Comparison with radiation-hydrodynamics modelsPlanet brightest away from anti-stellar point Knutson et al. 2007


Retrieval ResultsRetrieval Results

Dayside emission (subsolar)Dayside emission (subsolar)– Water (0.1-1 10Water (0.1-1 10-4-4))– Carbon monoxide (thermochemically very stable at Carbon monoxide (thermochemically very stable at

these P,Ts; CO=CH4 T=1100K at 1 bar)these P,Ts; CO=CH4 T=1100K at 1 bar) Also inferred from IRAC photometry (Charbonneau et al. 2008)Also inferred from IRAC photometry (Charbonneau et al. 2008) 1010-4-4

– Carbon dioxide (trace concentration 10Carbon dioxide (trace concentration 10-6-6)) CO+H2O <=> CO2+H2 (thermochemical in a CO field; CO+H2O <=> CO2+H2 (thermochemical in a CO field;

Lodders & Fegley 2002)Lodders & Fegley 2002) CO+OH <=> CO2+H (photochemical pathway)CO+OH <=> CO2+H (photochemical pathway)

– Methane upper limit (10Methane upper limit (10-7-7))– Significant residuals at the blue end of the spectrumSignificant residuals at the blue end of the spectrum


AbundancesAbundances

C/O is high and not well constrained (cloudless C/O is high and not well constrained (cloudless model)model)– 0.5 to 100.5 to 10

Solar 0.48 (Anders & Grevesse 1989)Solar 0.48 (Anders & Grevesse 1989)

Favor lower values because high C/O implies Favor lower values because high C/O implies disappearing water in CO fielddisappearing water in CO field

– Terminator Terminator (Swain, Vasisht, Tinetti 2008)(Swain, Vasisht, Tinetti 2008) Lower pressure depthsLower pressure depths Methane abundance is higher (CO < CH4) Methane abundance is higher (CO < CH4) Water 5.10Water 5.10-4-4

In SummaryIn Summary


Little evidence for …Little evidence for …

Hot Jovians not as “hot” as … good hot Curry !.Hot Jovians not as “hot” as … good hot Curry !.

ChemistryChemistry

Hot less dense atmospheres are more likely to show Hot less dense atmospheres are more likely to show abundant CO (and CO2 at lower T), while cooler, abundant CO (and CO2 at lower T), while cooler, denser ones show more abundant methane.denser ones show more abundant methane.

At 1 bar the CO=CH4 boundary is at T = 1125 K.At 1 bar the CO=CH4 boundary is at T = 1125 K. C/O atomic ratio is 0.48 (solar)C/O atomic ratio is 0.48 (solar)

14/08/200814/08/2008 Exeter Exoplanet WorkshopExeter Exoplanet Workshop

JPL-CITJPL-CIT Paris 2008Paris 2008Pont et al. 2008

JPL-CITJPL-CIT Paris 2008Paris 2008 F. Pont et al. 2008

Carbon & Oxygen ChemistryCarbon & Oxygen Chemistry

Major carbon bearing gases in a solar composition Major carbon bearing gases in a solar composition gas of given metallicity are generally CH4, CO gas of given metallicity are generally CH4, CO and/or CO2 depending on T and P.and/or CO2 depending on T and P.

14/08/200814/08/2008 Exeter Exoplanet WorkshopExeter Exoplanet Workshop

on nir hst spectro-photometry of transiting exo-planets

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