Author ORCID Identifier
Kimberly Ward-Duong: 0000-0002-4479-8291
Document Type
Article
Publication Date
5-1-2025
Publication Title
Astronomical Journal
Abstract
Giant planets generate accretion luminosity as they form. Much of this energy is radiated in strong Hα line emission, which has motivated direct imaging surveys at optical wavelengths to search for accreting protoplanets. However, compact disk structures can mimic accreting planets by scattering emission from the host star. This can complicate the interpretation of Hα point sources, especially if the host star itself is accreting. We describe an approach to distinguish accreting protoplanets from scattered-light disk features using “accretion light echoes.” This method relies on variable Hα emission from a stochastically accreting host star to search for a delayed brightness correlation with a candidate protoplanet. We apply this method to the candidate protoplanet AB Aur b with a dedicated Hubble Space Telescope Wide Field Camera 3 program designed to sequentially sample the host star and the candidate planet in Hα while accounting for the light travel time delay and orbital geometry of the source within the protoplanetary disk. Across five epochs spanning 14 months, AB Aur b is over 20 times more variable than its host star; AB Aur’s Hα emission changes by 15% while AB Aur b varies by 330%. These brightness changes are not correlated, which rules out unobstructed scattered starlight from the host star as the only source of AB Aur b’s Hα emission and is consistent with tracing emission from an independently accreting protoplanet, inner disk shadowing effects, or a physically evolving compact disk structure. More broadly, accretion light echoes offer a novel tool to explore the nature of protoplanet candidates with well-timed observations of the host star prior to deep imaging in Hα.
Volume
169
Issue
5
DOI
10.3847/1538-3881/adb6a1
ISSN
00046256
Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 International License.
Rights
©2025 The Authors
Recommended Citation
Bowler, Brendan P.; Zhou, Yifan; Biddle, Lauren I.; Jiang, Lillian Yushu; Bae, Jaehan; Close, Laird M.; Follette, Katherine B.; Franson, Kyle; Kraus, Adam L.; Sanghi, Aniket; Tran, Quang; Ward-Duong, Kimberly; Wu, Ya Lin; and Zhu, Zhaohuan, "Hα Variability of AB Aur b with the Hubble Space Telescope: Probing the Nature of a Protoplanet Candidate with Accretion Light Echoes" (2025). Astronomy: Faculty Publications, Smith College, Northampton, MA.
https://scholarworks.smith.edu/ast_facpubs/137
Comments
Archived as published.