Thermal emission from WASP-24b at 3.6 and 4.5 μm
Abstract
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.
Citation
Smith , A M S , Anderson , D R , Madhusudhan , N , Southworth , J , Cameron , A C , Blecic , J , Harrington , J , Hellier , C , Maxted , P F L , Pollacco , D , Queloz , D , Smalley , B , Triaud , A H M J & Wheatley , P J 2012 , ' Thermal emission from WASP-24b at 3.6 and 4.5 μm ' , Astronomy & Astrophysics , vol. 545 . https://doi.org/10.1051/0004-6361/201219294
Publication
Astronomy & Astrophysics
Status
Peer reviewed
ISSN
0004-6361Type
Journal article
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