This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
JPL-CITJPL-CIT Paris 2008Paris 2008
On NIR HST Spectro-photometry of On NIR HST Spectro-photometry of Transiting Exo-planets Transiting Exo-planets
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)
– 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
JPL-CITJPL-CIT Paris 2008Paris 2008
Hot, Cold or CloudyHot, Cold or Cloudy
JPL-CITJPL-CIT Paris 2008Paris 2008
Seager et al. 2005
Homogenous clouds
Hot T = 1750 K dayside reradiation
Active (common) C,N,O moleculesActive (common) C,N,O molecules
JPL-CITJPL-CIT Paris 2008Paris 2008
Lodders & Fegley 2002
JPL-CITJPL-CIT Paris 2008Paris 2008
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
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
€
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
JPL-CITJPL-CIT Paris 2008Paris 2008
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
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)
JPL-CITJPL-CIT Paris 2008Paris 2008
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
JPL-CITJPL-CIT Paris 2008Paris 2008
dx, dy, dθdx, dy, dθ
dTdT
Σ
dσdσ
dIdI
JPL-CITJPL-CIT Paris 2008Paris 2008
JPL-CITJPL-CIT Paris 2008Paris 2008
JPL-CITJPL-CIT Paris 2008Paris 2008
Orbit 1
JPL-CITJPL-CIT Paris 2008Paris 2008
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
JPL-CITJPL-CIT Paris 2008Paris 2008
Part III – Observations of HD 189733bPart III – Observations of HD 189733b
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))
JPL-CITJPL-CIT Paris 2008Paris 2008
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)
Showman et al. 2008Comparison with radiation-hydrodynamics modelsPlanet brightest away from anti-stellar point Knutson et al. 2007
JPL-CITJPL-CIT Paris 2008Paris 2008
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;
– 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
JPL-CITJPL-CIT Paris 2008Paris 2008
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
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)
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.