CaltechAUTHORS
Published April 20, 2025 | Version Published
Journal Article Open

Revealing a Main-sequence Star that Consumed a Planet with JWST

Creators

  • 1. ROR icon NOIRLab
  • 2. ROR icon Infrared Processing and Analysis Center
  • 3. ROR icon Vassar College
  • 4. ROR icon Massachusetts Institute of Technology
  • 5. ROR icon Space Telescope Science Institute
  • 6. ROR icon Arkansas Tech University
  • 7. ROR icon California Institute of Technology
  • 8. ROR icon Harvard-Smithsonian Center for Astrophysics
  • 9. ROR icon Jet Propulsion Lab

Abstract

The subluminous red nova (SLRN) Zwicky Transient Facility (ZTF) SLRN-2020 is the most compelling direct detection of a planet being consumed by its host star, a scenario known as a planetary engulfment event. We present JWST spectroscopy of ZTF SLRN-2020 taken +830 days after its optical emission peak using the NIRSpec fixed-slit 3–5 μm high-resolution grating and the MIRI 5–12 μm low-resolution spectrometer. NIRSpec reveals the 12CO fundamental band (ν = 1–0) in emission at ∼4.7 μm, Brackett-α emission, and the potential detection of PH3 in emission at ∼4.3 μm. The JWST spectra are consistent with the claim that ZTF SLRN-2020 arose from a planetary engulfment event. We utilize DUSTY to model the late-time ∼1–12 μm spectral energy distribution (SED) of ZTF SLRN-2020, where the best-fit parameters indicate the presence of warm, 720_(−50)^(+80) K, circumstellar dust with a total dust mass of Log (M/dM⊙)=−10.61_(−0.16)^(+0.08) M⊙. We also fit a DUSTY model to archival photometry taken +320 days after the peak that suggested the presence of a cooler, Td=280_(−20)^(+450) K, and more massive, Log (Md/M⊙)=−5.89_(−3.21)^(+0.29), circumstellar dust component. Assuming the cool component originates from the ZTF SLRN-2020 ejecta, we interpret the warm component as fallback from the ejecta. From the late-time SED model, we measure a luminosity of L∗=0.29_(−0.06)^(+0.03) L⊙ for the remnant host star, which is consistent with a ∼0.7 M⊙ K-type star that should not yet have evolved off the main sequence. If ZTF SLRN-2020 was not triggered by stellar evolution, we suggest that the planetary engulfment was due to orbital decay from tidal interactions between the planet and the host star.

Copyright and License

© 2025. The Author(s). Published by the American Astronomical Society.

Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

Acknowledgement

We thank our JWST program coordinator Shelly Meyett for facilitating our target of opportunity (ToO) Activation Request, which was one of the first ToO triggers with JWST. We also thank Sarah Kendrew for the valuable feedback on the reduction and analysis of the MIRI LRS observations. We also thank Greg Sloan for his review and feedback on our offset target acquisition strategy for the MIRI LRS observations. R.M.L. would like to acknowledge Joan Najita, J.J. Zanazzi, and Viraj Karambelkar for enlightening discussions on circumstellar disks, planetary engulfment events, and stellar mergers. R.M.L. also thanks Sarah Logsdon and Everett Schlawin for the helpful discussions on exoplanets.

This work is based on observations made with the NASA/ESA/CSA James Webb Space Telescope. The data were obtained from the Mikulski Archive for Space Telescopes at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-03127 for JWST. These observations are associated with program No. 1240.

Some of the data presented in this article were obtained from the MAST at the Space Telescope Science Institute. The specific observations analyzed can be accessed via doi:10.17909/198x-0r66.

This work is based on observations obtained at the international Gemini Observatory, a program of NSF NOIRLab, which is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the U.S. National Science Foundation on behalf of the Gemini Observatory partnership: the U.S. National Science Foundation (United States), National Research Council (Canada), Agencia Nacional de Investigación y Desarrollo (Chile), Ministerio de Ciencia, Tecnologìa e Innovación (Argentina), Ministério da Ciência, Tecnologia, Inovações e Comunicações (Brazil), and Korea Astronomy and Space Science Institute (Republic of Korea). The work of R.M.L. is supported by NOIRLab.

K.D. was supported by NASA through the NASA Hubble Fellowship grant No. HST-HF2-51477.001 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. M.M. is grateful for support from a Clay Postdoctoral Fellowship at the Smithsonian Astrophysical Observatory.

Facilities

JWST/MIRI - , JWST/NIRSpec - , Gemini-N/NIRI - .

Files

Lau_2025_ApJ_983_87.pdf

Files (1.5 MB)

Name Size Download all
md5:60cc486836d9ee933c931b087de804f0
1.5 MB Preview Download

Additional details

Related works

Is new version of
Discussion Paper: arXiv:2504.07275 (arXiv)
Is supplemented by
Dataset: 10.17909/198x-0r66 (DOI)

Funding

National Aeronautics and Space Administration
NAS 5-03127
NSF's NOIRLab
National Aeronautics and Space Administration
HST-HF2-51477.001
Space Telescope Science Institute
National Aeronautics and Space Administration
NAS5-26555
Smithsonian Astrophysical Observatory
Clay Postdoctoral Fellowship -

Dates

Accepted
2025-01-31
Available
2025-04-10
Published

Caltech Custom Metadata

Caltech groups
Astronomy Department, Infrared Processing and Analysis Center (IPAC), Division of Physics, Mathematics and Astronomy (PMA)
Publication Status
Published