Observations of HD189733b in Eclipse

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Observations of HD189733b in Eclipse

• G. Vasisht (JPL-Caltech) Collaborators

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Spectroscopy from space

• Nicmos allows objective mode spectro-photometry
  of transiting planets from 0.8-2.5 microns
• On orbit effects make the photometry unstable for
  DR gt 103
• Can it be made better?
• Can the instabilities really be corrected
  ex-post-facto?

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Introduction to NICMOS

• Multipurpose NIR Instrument
• Three cameras with NICMOS-3 focal planes
• NIC3 has grisms G096, G141, G206
• This talk G206
• Exoplanet datasets have now been acquired with
  all grisms
• G141 on HD 209548b (Brown et al. 2005)

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Scientific Rationale

• G206 range 1.45-2.55 microns
• For transmission spectroscopy
• Molecular transitions
• Most species i.e. the hydrides of O,C,N,S or
  oxides have overtone or fundamental bands
• Some immunity from scattering opacity
• Reasonable contrast for T103 photospheres for
  dayside emission

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Photometry with NICMOS

• Differential is easier than absolute
• Even so sources of error are a-plenty

Figer et al. 2004
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Structure in the Response
NIC-3 is under-sampled Defocus provides
some Immunity For G206 this sets R 40
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Structure in sub-Pixel Response
Finger et al. 2000
Stiavelli et al.
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Photometry
Evaluate in some statistical fashion
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Photometric errors
Variance depends on the power-spectral density of
the focal plane array Apodized by a filter
function
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Diffraction
Intrapixel gain var
PSF
Defocused PSF by Ray Tracing Note this is a PSD
1-cos(k dx), dx 0.1 pix
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What this means

• Substructure in the PSF
• On scales of D/?, D/2? etc
• Due to diffraction
• D/? 1/pixel
• Scales with wavelength
• For shorter ?, smaller scales
• Can interact with subpixel structure

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?

• Beam wander
• In x and y
• Repositioning errors
• Filter wheel positioning
• Rot. about undeviated ray
• PSF variation
• Proxy Gaussian width
• Array response variations
• temperature of the detector
• 1/K (2.5 micron), 3/K (1.5 micron)

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• Nicmos data are of mixed quality
• Troublesome first orbit
• G206 versus G141
• Positioning of the filter wheel
• G206 positioning settles better?
• with dx ? 0.1 pix versus 0.5 pix
• smaller rotational errors in the dispersion
  axis

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Pont et al.
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F. Pont et al.
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Orbit 1
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Other Systematics

• Optical effects
• Flux-migration between grating-orders
• Response of interference filter
• Geometrical shadowing by grooves
• Woods anomalies

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State-Variables HD189733b
angle
position
defocus
temperature
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Lightcurves
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Noise
Light curve
Design Matrix
Model vector
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Data Modeling-III
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Spectral Modelling

• Retrieval using RT models using well established
  scheme (Goody Yung 1989)
• Disk-averaged radiative transfer models developed
  originally for Earthshine, Mars
• (Tinetti et al. 2006, 2007)
• Photochemistry (Caltech-JPL Kinetics model)
• Layer-by-layer (log P between -6 and 0)
• Input T-P profiles
• Chemical profiles

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HD189733b NIR Contrast Spectrum
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Contrast Spectrum Components
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Science Summary

• Dayside emission
• Water (ubiquitous, high VMR)
• Carbon monoxide (thermochemically very stable at
  these P,Ts also Charbonneau et al. 2008)
• Carbon dioxide (low VMR)
• COH2O ?? CO2H2
• COOH ?? CO2H
• Methane upper limit
• Residuals at the blue end of the spectrum