Effect of Spitzer/IRAC Systematic Noises on Secondary Eclipses of the Exoplanet HD 209458 b

We analyze infrared light curves for 13 secondary eclipses of the exoplanet HD 209458 b obtained by Spitzer/IRAC in the 3.6 μ m channel. We find that in addition to the well-known effect of intra-pixel sensitivity variations, inducing quasiperiodic noise, these data also contain red noise which in turn consists of two subcomponents that differ by their correlation timescale, 10–20 s and 5–10 min. We also show that a global model of the intra-pixel sensitivity effect can be constructed such that it can fit all 13 light curves at once but uses only a few parameters (e.g., 12 or so). Finally, we tried to measure the systematic time shift of the exoplanetary secondary eclipse, which appeared consistent with zero, -4± 40 s. This corresponds to a spatial shift of 0.007± 0.060 in units of planet radius, or to the orbital eccentricity ecosω of (-0.2± 2.1)× 10⁻⁴ .