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Time-resolved photometry is an important new probe of the physics ofcondensate clouds in extrasolar planets and brown dwarfs. Extreme adaptiveoptics systems can directly image planets, but precise brightness measurementsare challenging. We present VLT/SPHERE high-contrast, time-resolved broadH-band near-infrared photometry for four exoplanets in the HR 8799 system,sampling changes from night to night over five nights with relatively shortintegrations. The photospheres of these four planets are often modeled bypatchy clouds and may show large-amplitude rotational brightness modulations.Our observations provide high-quality images of the system. We present adetailed performance analysis of different data analysis approaches toaccurately measure the relative brightnesses of the four exoplanets. We explorethe information in satellite spots and demonstrate their use as a proxy forimage quality. While the brightness variations of the satellite spots arestrongly correlated, we also identify a second-order anti-correlation patternbetween the different spots. Our study finds that PCA-based KLIP reduction withsatellite spot-modulated artificial planet-injection based photometry (SMAP)leads to a significant (~3x) gain in photometric accuracy over standardaperture-based photometry and reaches 0.1 mag per point accuracy for ourdataset, the signal-to-noise of which is limited by small field rotation.Relative planet-to-planet photometry can be compared be- tween nights, enablingobservations spanning multiple nights to probe variability. Recent high-qualityrelative H-band photometry of the b-c planet pair agree to about 1%.

astrophysical journal/the astrophysical journal

High-Cadence, High-Contrast Imaging for Exoplanet Mapping: Observations  of the HR 8799 Planets with VLT/SPHERE Satellite Spot-Corrected Relative  Photometry