Thermal emission at 4.5 and 8 μm of WASP-17b, an extremely large planet in a slightly eccentric orbit

We report the detection of thermal emission at 4.5 and 8 μm from the planet WASP-17b. We used Spitzer to measure the system brightness at each wavelength during two occultations of the planet by its host star. By combining the resulting light curves with existing transit light curves and radial-velo...

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Bibliographic Details
Published in:Monthly notices of the Royal Astronomical Society 2011-09, Vol.416 (3), p.2108-2122
Main Authors: Anderson, D. R., Smith, A. M. S., Lanotte, A. A., Barman, T. S., Cameron, A. Collier, Campo, C. J., Gillon, M., Harrington, J., Hellier, C., Maxted, P. F. L., Queloz, D., Triaud, A. H. M. J., Wheatley, P. J.
Format: Article
Language:English
Subjects:
Astronomy
Brightness
Earth, ocean, space
Eccentric orbits
Eccentricity
Eccentrics
Exact sciences and technology
Extrasolar planets
Heating
methods: data analysis
occultations
planets and satellites: atmospheres
planets and satellites: individual: WASP-17b
stars: individual: WASP-17
techniques: photometric
Thermal emission
Transit
Citations: Items that cite this one
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Summary:We report the detection of thermal emission at 4.5 and 8 μm from the planet WASP-17b. We used Spitzer to measure the system brightness at each wavelength during two occultations of the planet by its host star. By combining the resulting light curves with existing transit light curves and radial-velocity measurements in a simultaneous analysis, we find the radius of WASP-17b to be 2.0R Jup, which is 0.2R Jup larger than any other known planet and 0.7R Jup larger than predicted by the standard cooling theory of irradiated gas giant planets. We find the retrograde orbit of WASP-17b to be slightly eccentric, with 0.0012 < e < 0.070 (3σ). Such a low eccentricity suggests that, under current models, tidal heating alone could not have bloated the planet to its current size, so the radius of WASP-17b is currently unexplained. From the measured planet-star flux-density ratios we infer 4.5 and 8 μm brightness temperatures of 1881 ± 50 and 1580 ± 150 K, respectively, consistent with a low-albedo planet that efficiently redistributes heat from its day side to its night side.
ISSN:0035-8711
1365-2966
DOI:10.1111/j.1365-2966.2011.19182.x