Gibson, N. P. and Aigrain, S. and Pont, F. and Sing, D. K. and Désert, J. M. and Evans, T. M. and Henry, G. and Husnoo, N. and Knutson, H. (2012) Probing the haze in the atmosphere of HD 189733b with Hubble Space Telescope/WFC3 transmission spectroscopy. Monthly Notices of the Royal Astronomical Society, 422 (1). pp. 753-760. ISSN 0035-8711 http://resolver.caltech.edu/CaltechAUTHORS:20120611-153352421
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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.
|Additional Information:||© 2012 The Authors. Monthly Notices of the Royal Astronomical Society. © 2012 RAS. Accepted 2012 January 30. Received 2012 January 27; in original form 2012 January 12. All of the data presented in this paper were obtained from the Multimission Archive at the Space Telescope Science Institute (MAST). STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Support for MAST for non-HST data is provided by the NASA Office of Space Science via grant NNX09AF08G and by other grants and contracts. NPG and SA acknowledge support from STFC grant ST/G002266/2. We are extremely grateful for the support provided the WFC3 instrument team, in particular H. Bushouse, and discussions with P. McCullough. Finally, we thank the referee, R. Gilliland, for his careful reading of the manuscript and helpful suggestions.|
|Subject Keywords:||methods: data analysis; techniques: spectroscopic; stars: individual:HD189733; planetary systems|
|Official Citation:||Gibson, N. P., Aigrain, S., Pont, F., Sing, D. K., Désert, J.-M., Evans, T. M., Henry, G., Husnoo, N. and Knutson, H. (2012), Probing the haze in the atmosphere of HD 189733b with Hubble Space Telescope/WFC3 transmission spectroscopy. Monthly Notices of the Royal Astronomical Society, 422: 753–760. doi: 10.1111/j.1365-2966.2012.20655.x|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Jason Perez|
|Deposited On:||14 Jun 2012 17:30|
|Last Modified:||18 Jan 2013 23:19|
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