Ultraviolet Imaging of SR 12 c with HST/WFC3: Accretion and Variability of a Giant Planet at the End Stages of Growth

Authors

• Claire O. Finley, University of Texas at Austin
• Brendan P. Bowler, University of Texas at Austin
• Ya-Lin Wu, National Taiwan Normal University
• Adam L. Kraus, University of Texas at Austin
• Yifan Zhou, University of Virginia
• Yuhiko Aoyama, Sun Yat-sen University
• William Best, University of Texas at Austin
• Ian Czekala, University of St. Andrews
• Catherine C. Espaillat, Boston University
• Katherine B. Follette, Amherst College
• Gregory J. Herczeg, Peking University
• Raquel A. Martinez, University of San Diego
• Connor E. Robinson, Boston University
• Quang H. Tran, Yale University
• K. Ward-Duong, Smith CollegeFollow

Author ORCID Identifier

Claire Finley: 0000-0002-9884-9584

Brendan Bowler: 0000-0003-2649-2288

Ya-Lin Wu: 0000-0002-4392-1446

Adam Kraus: 0000-0001-9811-568X

Yifan Zhou: 0000-0003-2969-6040

Yuhiko Aoyama: 0000-0003-0568-9225

William M. J. Best: 0000-0003-0562-1511

Ian Czekala: 0000-0002-1483-8811

Catherine Espaillat: 0000-0001-9227-5949

Katherine Follette: 0000-0002-7821-0695

Gregory Herczeg: 0000-0002-7154-6065

Raquel A. Martinez: 0000-0001-6301-896X

Connor Robinson: 0000-0003-1639-510X

Quang H. Tran: 0000-0001-6532-6755

Kimberly Ward-Duong: 0000-0002-4479-8291

Document Type

Article

Publication Date

8-2026

Publication Title

The Astronomical Journal

Abstract

Many details of the gas accretion phase during giant planet formation remain untested. We present new 0.2–0.7 μm UV-through-red optical imaging of the young, wide-orbit planetary-mass companion SR 12 c from the Wide Field Camera 3 (WFC3) instrument on board the Hubble Space Telescope. SR 12 c exhibits strong accretion-related continuum excess blueward of∼5000 Å and clear signs of the Balmer jump at 3646 Å. We derive a total accretion luminosity of1.65 ±0.19× 10⁻⁵L_⊙and a mass accretion rate of 8 ±2 × 10⁻¹² M_⊙yr⁻¹. Based on its mass and age,SR12 c will not grow by an appreciable amount at its current accretion rate; it is at the end stages of assembly. No accretion variability is evident between the two epochs of the WFC3 observations spanning a month-long baseline, but the Hαemission line strength decreases by 90% compared to the reported flux from five years earlier. Combined with previous observations of SR 12 c, we assemble one of the most complete spectral energy distributions of a young giant planet to date, spanning the UV through sub-mm wavelengths (0.2–880 μm). This adds SR 12 c to the small yet growing sample of planets with detailed accretion and disk constraints, which together are beginning to establish the diversity of timescales and physical processes governing the formation of giant planets.

Keywords

Extrasolar gaseous giant planets (509), Accretion (14), Exoplanet formation (492), Exoplanet astronomy (486), Planet formation (1241)

Volume

172

Issue

134

Creative Commons License

This work is licensed under a Creative Commons Attribution 4.0 International License.

Rights

© 2026. The Author(s). Published by the American Astronomical Society.

Version

Version of Record

Recommended Citation

Finley, Claire O.; Bowler, Brendan P.; Wu, Ya-Lin; Kraus, Adam L.; Zhou, Yifan; Aoyama, Yuhiko; Best, William; Czekala, Ian; Espaillat, Catherine C.; Follette, Katherine B.; Herczeg, Gregory J.; Martinez, Raquel A.; Robinson, Connor E.; Tran, Quang H.; and Ward-Duong, K., "Ultraviolet Imaging of SR 12 c with HST/WFC3: Accretion and Variability of a Giant Planet at the End Stages of Growth" (2026). Astronomy: Faculty Publications, Smith College, Northampton, MA.
https://scholarworks.smith.edu/ast_facpubs/157