Transit spectrophotometry of the exoplanet HD 189733b. I. Searching for water but finding haze with HST NICMOS
Sing, David K.; Desert, J.-M.; Lecavelier des Etangs, A.; et al.Ballester, G.; Vidal-Madjar, A.; Parmentier, V.; Hebrard, G.; Henry, G.
Date: 2009
Journal
Astronomy and Astrophysics
Publisher
EDP Sciences for European Southern Observatory (ESO)
Publisher DOI
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Abstract
We present Hubble Space Telescope near-infrared transit photometry of the nearby hot-Jupiter HD189733b. The observations were
taken with the NICMOS instrument during five transits, with three transits executed with a narrowband filter at 1.87 μm and two
performed with a narrowband filter at 1.66 μm. Our observing strategy using ...
We present Hubble Space Telescope near-infrared transit photometry of the nearby hot-Jupiter HD189733b. The observations were
taken with the NICMOS instrument during five transits, with three transits executed with a narrowband filter at 1.87 μm and two
performed with a narrowband filter at 1.66 μm. Our observing strategy using narrowband filters is insensitive to the usual HST intraorbit
and orbit-to-orbit measurement of systematic errors, allowing us to accurately and robustly measure the near-IR wavelength
dependance of the planetary radius. Our measurements fail to reproduce the previously claimed detection of an absorption signature
of atmospheric H2O below2 μm at a 5σ confidence level.We measure a planet-to-star radius contrast of 0.15498±0.00035 at 1.66 μm
and a contrast of 0.15517 ± 0.00019 at 1.87 μm. Both of our near-IR planetary radii values are in excellent agreement with the levels
expected from Rayleigh scattering by sub-micron haze particles, observed at optical wavelengths, indicating that upper-atmospheric
haze still dominates the near-IR transmission spectra over the absorption from gaseous molecular species at least below 2 μm.
Physics and Astronomy
Faculty of Environment, Science and Economy
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