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The atmospheres of gas giant planets are thought to be inhomogeneous due toweather and patchy clouds. We present two full nights of coronagraphicobservations of the HR 8799 planets using the CHARIS integral fieldspectrograph behind the SCExAO adaptive optics system on the Subaru Telescopeto search for spectrophomometric variability. We did not detect significantvariability signals, but placed the lowest variability upper limits for HR 8799c and d. Based on injection-recovery tests, we expected to have a 50% chance todetect signals down to 10% H-band photometric variability for HR 8799 c anddown to 30% H-band variability for HR 8799 d. We also investigated spectralvariability and expected a 50% chance to recovery 20% variability in the H/Kflux ratio for HR 8799 c. We combined all the data from the two nights toobtain some of the most precise spectra obtained for HR 8799 c, d, and e. Usinga grid of cloudy radiative-convective-thermochemical equilibrium models, wefound all three planets prefer supersolar metallicity with effectivetemperatures of ~1100 K. However, our high signal-to-noise spectra show that HR8799 d has a distinct spectrum from HR 8799 c, possibly preferring morevertically extended and uniform clouds and indicating that the planets are notidentical.

Atmospheric Monitoring and Precise Spectroscopy of the HR 8799 Planets with SCExAO/CHARIS