HST Observations of PDS 70

Data used in paper titled: Evidence for Variable Accretion onto PDS 70 c and Implications for Protoplanet Detections

Paper abstract: Understanding the processes of planet formation and accretion in young systems is essential to unraveling the initial conditions of planetary systems. The PDS\,70 system, which hosts two directly imaged protoplanets, provides a unique laboratory for studying these phenomena, particularly through accretion-tracing H$\alpha$ emission. The presented multi-epoch observations examine the variability in accretion signatures within this system, focusing on \pdsbc. Using Hubble Space Telescope narrowband H$\alpha$ imaging from 2020 and 2024, we achieve high signal-to-noise detection of these planets and reveal significant changes in H$\alpha$ flux. For \pdsc, the H$\alpha$ flux increases by $>2\times$ between 2020 and 2024. The trend is consistent with the one identified in recently published MagAO-X data, further confirming that \pdsc is becoming significantly brighter in H$\alpha$ in the past year. The observed variability suggests dynamic accretion processes, possibly modulated by circumplanetary disk properties or transient accretion bursts. Based on these findings, we quantify the impact of variability on the detectability of protoplanets in imaging surveys and emphasize the need for continued and regular monitoring to accurately assess the occurrence and characteristics of young, forming planets. High-amplitude variability in PDS 70 c motivates simultaneous monitoring of multiple accretion tracers to probe the mechanisms of mass growth of gas giant planets.