Evidence for Variable Accretion onto PDS 70 c and Implications for Protoplanet Detections

TL;DR

This study presents multi-epoch H-alpha observations of PDS 70 c, revealing significant accretion variability that impacts the detection and understanding of protoplanets in young systems.

Contribution

It provides the first evidence of variable accretion onto PDS 70 c through high-resolution imaging, highlighting the importance of monitoring for accurate planet characterization.

Findings

PDS 70 c's H-alpha flux more than doubled between 2020 and 2024

Significant accretion variability observed, consistent across multiple datasets

Variability suggests dynamic accretion processes influenced by circumplanetary disks

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 H-alpha emission a commonly used accretion tracer. We present multi-epoch observations and examine the variability in accretion signatures within this system, focusing on PDS 70 b and c. Using Hubble Space Telescope narrowband H-alpha imaging from 2020 and 2024, we achieve high signal-to-noise ratio detections of these planets and reveal significant changes in H-alpha flux. For PDS 70 c, the H-alpha flux more than doubled between 2020 and 2024. The trend is consistent with the one identified in recently published MagAO-X data, further confirming that PDS 70 c has become significantly brighter in H between 2023 March and 2024 May. The observed variability suggests dynamic accretion processes, possibly modulated by circumplanetary disk properties or transient accretion bursts. 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. 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.