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Published October 1, 2025 | Version Published
Journal Article Open

Very Late-time JWST and Keck Spectra of the Oxygen-rich Supernova 1995N

Creators

  • 1. ROR icon Space Science Institute
  • 2. ROR icon Louisiana State University
  • 3. ROR icon Maria Mitchell Association
  • 4. ROR icon Cardiff University
  • 5. ROR icon Space Telescope Science Institute
  • 6. ROR icon Johns Hopkins University
  • 7. ROR icon University of California, Berkeley
  • 8. ROR icon Infrared Processing and Analysis Center
  • 9. ROR icon Tsinghua University
  • 10. ROR icon Princeton University
  • 11. ROR icon University of Arizona
  • 12. Gemini Observatory, 670 N. Aohoku Place, Hilo, HI 96720, USA
  • 13. ROR icon University of Hawaii at Manoa
  • 14. ROR icon Ghent University
  • 15. ROR icon Institut d'Astrophysique de Paris
  • 16. ROR icon University of Maryland, College Park
  • 17. ROR icon Goddard Space Flight Center
  • 18. ROR icon University of California, Santa Cruz
  • 19. ROR icon Stockholm University
  • 20. ROR icon California Institute of Technology
  • 21. ROR icon University of Canterbury
  • 22. ROR icon NOIRLab
  • 23. ROR icon European Space Astronomy Centre
  • 24. ROR icon Purdue University West Lafayette
  • 25. ROR icon University of Copenhagen
  • 26. ROR icon University of Virginia
  • 27. ROR icon University of Szeged
  • 28. MTA-ELTE Lendület "Momentum" Milky Way Research Group, Szent Imre H. st. 112, 9700 Szombathely, Hungary
  • 29. ROR icon National Astronomical Research Institute of Thailand
  • 30. ROR icon Massachusetts Institute of Technology
  • 31. ROR icon Hebei University
  • 32. ROR icon Konkoly Observatory

Abstract

We present new JWST/MIRI Medium Resolution Spectroscopy and Keck spectra of SN 1995N obtained in 2022–2023, more than 10,000 days after the supernova (SN) explosion. These spectra are among the latest direct detections of a core-collapse SN, both through emission lines in the optical and thermal continuum from infrared (IR) dust emission. The new IR data show that dust heating from radiation produced by the ejecta interacting with circumstellar matter is still present but greatly reduced from when SN 1995N was observed by the Spitzer Space Telescope and WISE in 2009/2010 and 2018, when the dust mass was estimated to be 0.4 M⊙. New radiative-transfer modeling suggests that the dust mass and grain size may have increased between 2010 and 2023. The new data can alternatively be well fit with a dust mass of 0.4 M⊙ and a much reduced heating source luminosity. The new late-time spectra show unusually strong oxygen forbidden lines, stronger than the Hα emission. This indicates that SN 1995N may have exploded as a stripped-envelope SN, which then interacted with a massive H-rich circumstellar shell, changing it from intrinsically Type Ib/c to Type IIn. The late-time spectrum results when the reverse shock begins to excite the inner H-poor, O-rich ejecta. This change in the spectrum is rarely seen but marks the start of the transition from SN to SN remnant.

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 the anonymous referee for suggestions that have improved the paper. This work is based (in part) 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. The observations are associated with program GO-1860.

The specific observations analyzed can be accessed via doi:10.17909/04jm-tx25. Support to MAST for these data is provided by the NASA Office of Space Science via grant NAG5-7584 and by other grants and contracts.

Partial support for this work was provided by NASA grant JWST-GO-02666.002-A. S.Z. received support from the NKFIH OTKA K142534 grant. A.V.F.’s research group at UC Berkeley acknowledges financial assistance from the Christopher R. Redlich Fund, as well as donations from Gary and Cynthia Bengier, Clark and Sharon Winslow, Alan Eustace and Kathy Kwan, William Draper, Timothy and Melissa Draper, Briggs and Kathleen Wood, and Sanford Robertson (W.Z. is a Bengier-Winslow-Eustace Specialist in Astronomy, T.G.B. is a Draper-Wood-Robertson Specialist in Astronomy, Y.Y. was a Bengier-Winslow-Robertson Fellow in Astronomy), and many other donors. D.M. acknowledges support from the National Science Foundation (NSF) through grants PHY-2209451 and AST-2206532.

The W. M. Keck Observatory is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA; the observatory was made possible by the generous financial support of the W. M. Keck Foundation. The Kast spectrograph on the Shane 3 m telescope at Lick Observatory was made possible through a generous gift from William and Marina Kast. We acknowledge the excellent assistance of the staff at each of Keck and Lick Observatories.

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Additional details

Related works

Is new version of
Discussion Paper: arXiv:2505.01574 (arXiv)
Is supplemented by
Dataset: 10.17909/04jm-tx25 (DOI)

Funding

National Aeronautics and Space Administration
NAS 5-03127
National Aeronautics and Space Administration
NAG5-7584
National Aeronautics and Space Administration
JWST-GO-02666.002-A
National Research, Development and Innovation Office
K142534
University of California, Berkeley
National Science Foundation
PHY-2209451
National Science Foundation
AST-2206532
W. M. Keck Foundation

Dates

Accepted
2025-08-14
Available
2025-09-23
Published online

Caltech Custom Metadata

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