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Title: Water vapor in the spectrum of the extrasolar planet HD 189733b. I. The transit

We report near-infrared spectroscopy of the gas giant planet HD 189733b in transit. We used the Hubble Space Telescope Wide Field Camera 3 (HST WFC3) with its G141 grism covering 1.1 μm to 1.7 μm and spatially scanned the image across the detector at 2'' s{sup –1}. When smoothed to 75 nm bins, the local maxima of the transit depths in the 1.15 μm and 1.4 μm water vapor features are, respectively, 83 ± 53 ppm and 200 ± 47 ppm greater than the local minimum at 1.3 μm. We compare the WFC3 spectrum with the composite transit spectrum of HD 189733b assembled by Pont et al., extending from 0.3 μm to 24 μm. Although the water vapor features in the WFC3 spectrum are compatible with the model of non-absorbing, Rayleigh-scattering dust in the planetary atmosphere, we also re-interpret the available data with a clear planetary atmosphere. In the latter interpretation, the slope of increasing transit depth with shorter wavelengths from the near infrared, through the visible, and into the ultraviolet is caused by unocculted star spots, with a smaller contribution of Rayleigh scattering by molecular hydrogen in the planet's atmosphere. At relevant pressures along the terminator, our model planetarymore » atmosphere's temperature is ∼700 K, which is below the condensation temperatures of sodium- and potassium-bearing molecules, causing the broad wings of the spectral lines of Na I and K I at 0.589 μm and 0.769 μm to be weak.« less
Authors:
;  [1] ;  [2] ;  [3]
  1. Space Telescope Science Institute, Baltimore, MD 21218 (United States)
  2. Department of Astronomy, University of Maryland, College Park, MD 20742 (United States)
  3. Yale Center for Astronomy and Astrophysics, Yale University, New Haven, CT 06511 (United States)
Publication Date:
OSTI Identifier:
22365377
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 791; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION SPECTROSCOPY; COMPARATIVE EVALUATIONS; COVERINGS; DUSTS; HYDROGEN; IMAGES; INFRARED SPECTRA; MOLECULES; PLANETARY ATMOSPHERES; PLANETS; RAYLEIGH SCATTERING; SATELLITE ATMOSPHERES; SODIUM; SPACE; STARS; TELESCOPES; ULTRAVIOLET RADIATION; WATER VAPOR; WAVELENGTHS