Abstract
We present Hubble Space Telescope near-infrared transmission
spectroscopy of the transiting exoplanet HD 189733b, using the Wide
Field Camera 3 (WFC3). This consists of time series spectra of two
transits, used to measure the wavelength dependence of the planetary
radius. These observations aim to test whether the Rayleigh scattering
haze detected at optical wavelengths extends into the near-infrared, or
if it becomes transparent leaving molecular features to dominate the
transmission spectrum. Due to saturation and non-linearity affecting the
brightest (central) pixels of the spectrum, light curves were extracted
from the blue and red ends of the spectra only, corresponding to
wavelength ranges of 1.099-1.168 and 1.521-1.693 μm, respectively,
for the first visit, and 1.082-1.128 and 1.514-1.671 μm for the
second. The light curves were fitted using a Gaussian process model to
account for instrumental systematics whilst simultaneously fitting for
the transit parameters. This gives values of the planet-to-star radius
ratio for the blue and red light curves of 0.156 50 ± 0.000 48
and 0.156 34 ± 0.000 32, respectively, for visit 1 and 0.157 16
± 0.000 78 and 0.156 30 ± 0.000 37 for visit 2 (using a
quadratic limb-darkening law). The planet-to-star radius ratios measured
in both visits are consistent, and we see no evidence for the drop in
absorption expected if the haze that is observed in the optical becomes
transparent in the infrared. This tentatively suggests that the haze
dominates the transmission spectrum of HD 189733b into near-infrared
wavelengths, although more robust observations are required to provide
conclusive evidence.
Original language | English |
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Pages (from-to) | 753-760 |
Journal | Monthly Notices of the Royal Astronomical Society |
Volume | 422 |
Issue number | 1 |
Early online date | 12 Jan 2012 |
DOIs | |
Publication status | Published - 01 May 2012 |
Externally published | Yes |
Keywords
- methods: data analysis
- techniques: spectroscopic
- stars: individual: HD 189733
- planetary systems