MagAO-X and HST high-contrast imaging of the AS209 disk at H$\alpha$

TL;DR

This study used MagAO-X and HST to search for Hα emission from a protoplanet candidate around AS209, setting limits on its accretion and revealing a jet, demonstrating ground-based systems' potential for high-contrast imaging.

Contribution

First combined use of MagAO-X and HST to constrain accretion in a protoplanet candidate and image a jet, highlighting ground-based system capabilities.

Findings

No Hα emission detected from the candidate, with flux limits below previous space-based measurements.

Detected a jet north of the star consistent with previous forbidden line observations.

Ground-based adaptive optics can outperform space telescopes in high-contrast imaging of protoplanets.

Abstract

The detection of emission lines associated with accretion processes is a direct method for studying how and where gas giant planets form, how young planets interact with their natal protoplanetary disk and how volatile delivery to their atmosphere takes place. H$\alpha$ ($\lambda=0.656\,\mu$m) is expected to be the strongest accretion line observable from the ground with adaptive optics systems, and is therefore the target of specific high-contrast imaging campaigns. We present MagAO-X and HST data obtained to search for H$\alpha$ emission from the previously detected protoplanet candidate orbiting AS209, identified through ALMA observations. No signal was detected at the location of the candidate, and we provide limits on its accretion. Our data would have detected an H$\alpha$ emission with $F_\mathrm{H\alpha}>2.5\pm0.3 \times10^{-16}$ erg s$^{-1}$ cm$^{-2}$, a factor 6.5 lower than the HST flux measured for PDS70b (Zhou et al., 2021). The flux limit indicates that if the protoplanet is currently accreting it is likely that local extinction from circumstellar and circumplanetary material strongly attenuates its emission at optical wavelengths. In addition, the data reveal the first image of the jet north of the star as expected from previous detections of forbidden lines. Finally, this work demonstrates that current ground-based observations with extreme adaptive optics systems can be more sensitive than space-based observations, paving the way to the hunt for small planets in reflected light with extremely large telescopes.