Diffuser-assisted Infrared Transit Photometry for Four Dynamically Interacting Kepler Systems

We present ground-based infrared transit observations for four dynamically interacting Kepler planets, including Kepler-29b, Kepler-36c, KOI-1783.01, and Kepler-177c, obtained using the Wide-field Infrared Camera on the Hale 200 inch telescope at Palomar Observatory. By utilizing an engineered diffuser and custom guiding software, we mitigate time-correlated telluric and instrumental noise sources in these observations. We achieve an infrared photometric precision comparable to or better than that of space-based observatories such as the Spitzer Space Telescope, and detect transits with greater than 3σ significance for all planets. For Kepler-177c (J = 13.9), our measurement uncertainties are only 1.2 times the photon noise limit and 1.9 times better than the predicted photometric precision for Spitzer IRAC photometry of this same target. We find that a single transit observation obtained 4–5 yr after the end of the original Kepler mission can reduce dynamical mass uncertainties by as much as a factor of 3 for these systems. Additionally, we combine our new observations of KOI-1783.01 with information from the literature to confirm the planetary nature of this system. We discuss the implications of our new mass and radius constraints in the context of known exoplanets with low incident fluxes, and we note that Kepler-177c may be a more massive analog to the currently known super-puffs given its core mass (3.8 ± 0.9 M⊙) and large gas-to-core ratio (2.8 ± 0.7). Our demonstrated infrared photometric performance opens up new avenues for ground-based observations of transiting exoplanets previously thought to be restricted to space-based investigation.