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The Emergent 1.1-1.7 μm Spectrum of the Exoplanet CoRoT-2b as Measured Using the Hubble Space Telescope

Author(s): Wilkins, Ashlee N; Deming, Drake; Madhusudhan, Nikku; Burrows, Adam S.; Knutson, Heather A.; et al

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Abstract: We have used Hubble/WFC3 and the G141 grism to measure the secondary eclipse of the transiting, very hot Jupiter CoRoT-2b in the 1.1–1.7μm spectral region. We find an eclipse depth averaged over this band equal to 395+69−45parts per million, equivalent to a blackbody temperature of 1788±18 K. We study and characterize several WFC3 instrumental effects, especially the “hook” phenomenon described by Deming et al. We use data from several transiting exoplanet systems to find a quantitative relation between the amplitude of the hook and the exposure level of a given pixel. Although the uncertainties in this relation are too large to allow us to develop an empirical correction for our data, our study provides a useful guide for optimizing exposure levels in future WFC3 observations. We derive the planet’s spectrum using a differential method. The planet-to-star contrast increases to longer wavelength within the WFC3 bandpass, but without water absorption or emission to a 3σlimit of 85 ppm. The slope of theWFC3 spectrum is significantly less than the slope of the best-fit blackbody. We compare all existing eclipse data for this planet to a blackbody spectrum, and to spectra from both solar abundance and carbon-rich (C/O=1) models.A blackbody spectrum is an acceptable fit to the full data set. Extra continuous opacity due to clouds or haze, and flattened temperature profiles, are strong candidates to produce quasi-blackbody spectra, and to account for the amplitude of the optical eclipses. Our results show ambiguous evidence for a temperature inversion in this planet.
Publication Date: 10-Mar-2014
Electronic Publication Date: 21-Feb-2014
Citation: Wilkins, Ashlee N, Deming, Drake, Madhusudhan, Nikku, Burrows, Adam, Knutson, Heather, McCullough, Peter, Ranjan, Sukrit. (2014). The Emergent 1.1-1.7 \ensuremathμm Spectrum of the Exoplanet CoRoT-2b as Measured Using the Hubble Space Telescope. apj, 783 (113 - 113. doi:10.1088/0004-637X/783/2/113
DOI: doi:10.1088/0004-637X/783/2/113
Type of Material: Journal Article
Journal/Proceeding Title: Astrophysical Journal
Version: Final published version. This is an open access article.

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