WARM SPITZER AND PALOMAR NEAR-IR SECONDARY ECLIPSE PHOTOMETRY OF TWO HOT JUPITERS: WASP-48b AND HAT-P-23b

We report secondary eclipse photometry of two hot Jupiters, WASP-48b and HAT-P-23b, at 3.6 and 4.5 mu m taken with the InfraRed Array Camera aboard the Spitzer Space Telescope during the warm Spitzer mission and in the H and K sub(S) bands with the Wide Field IR Camera at the Palomar 200 inch Hale Telescope. WASP-48b and HAT-P-23b are Jupiter-mass and twice Jupiter-mass objects orbiting an old, slightly evolved F star and an early G dwarf star, respectively. In the H, K sub(S), 3.6 mu m, and 4.5 mu m bands, respectively, we measure secondary eclipse depths of 0.047% plus or minus 0.016%, 0.109% plus or minus 0.027%, 0.176% plus or minus 0.013%, and 0.214% plus or minus 0.020% for WASP-48b. In the K sub(S), 3.6 mu m, and 4.5 mu m bands, respectively, we measure secondary eclipse depths of 0.234% plus or minus 0.046%, 0.248% plus or minus 0.019%, and 0.309% plus or minus 0.026% for HAT-P-23b. For WASP-48b and HAT-P-23b, respectively, we measure delays of 2.6 plus or minus 3.9 minutes and 4.0 plus or minus 2.4 minutes relative to the predicted times of secondary eclipse for circular orbits, placing 2[sigma] upper limits on |e cos omega | of 0.0053 and 0.0080, both of which are consistent with circular orbits. The dayside emission spectra of these planets are well-described by blackbodies with effective temperatures of 2158 plus or minus 100 K (WASP-48b) and 2154 plus or minus 90 K (HAT-P-23b), corresponding to moderate recirculation in the zero albedo case. Our measured eclipse depths are also consistent with one-dimensional radiative transfer models featuring varying degrees of recirculation and weak thermal inversions or no inversions at all. We discuss how the absence of strong temperature inversions on these planets may be related to the activity levels and metallicities of their host stars.