Volume 545, September 2012
|Number of page(s)||7|
|Section||Planets and planetary systems|
|Published online||12 September 2012|
Thermal emission from WASP-24b at 3.6 and 4.5 μm
Astrophysics Group, Lennard-Jones LaboratoriesKeele
2 Department of Physics, and Department of Astronomy, Yale University, New Haven, CT 06511, USA
3 SUPA, School of Physics and Astronomy, University of St. Andrews, North Haugh, St. Andrews, Fife, KY16 9SS, UK
4 Planetary Sciences Group, Department of Physics, University of Central Florida, Orlando, FL 32816-2385, USA
5 Astrophysics Research Centre, Physics Building, Queen’s University, Belfast, County Antrim, BT7 1NN, UK
6 Observatoire de Genève, Université de Genève, 51 Chemin des Maillettes, 1290 Sauverny, Switzerland
7 Department of Physics, University of Warwick, Coventry CV4 7AL, UK
Received: 23 March 2012
Accepted: 17 August 2012
Aims. We observe occultations of WASP-24b to measure brightness temperatures and to determine whether or not its atmosphere exhibits a thermal inversion (stratosphere).
Methods. We observed occultations of WASP-24b at 3.6 and 4.5 μm using the Spitzer Space Telescope. It has been suggested that there is a correlation between stellar activity and the presence of inversions, so we analysed existing HARPS spectra in order to calculate log R′HK for WASP-24 and thus determine whether or not the star is chromospherically active. We also observed a transit of WASP-24b in the Strömgren u and y bands, with the CAHA 2.2-m telescope.
Results. We measure occultation depths of 0.159 ± 0.013 per cent at 3.6 μm and 0.202 ± 0.018 per cent at 4.5 μm. The corresponding planetary brightness temperatures are 1974 ± 71 K and 1944 ± 85 K respectively. Atmosphere models with and without a thermal inversion fit the data equally well; we are unable to constrain the presence of an inversion without additional occultation measurements in the near-IR. We find log R′HK = −4.98 ± 0.12, indicating that WASP-24 is not a chromospherically active star. Our global analysis of new and previously-published data has refined the system parameters, and we find no evidence that the orbit of WASP-24b is non-circular.
Conclusions. These results emphasise the importance of complementing Spitzer measurements with observations at shorter wavelengths to gain a full understanding of hot Jupiter atmospheres.
Key words: planetary systems / planets and satellites: atmospheres / stars: individual: WASP-24 / planets and satellites: individual: WASP-24b / infrared: planetary systems
© ESO, 2012
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