We demonstrate proof of concept of a new strategy for studying infrared (IR) transients enabled by the newly launched SPHEREx space mission, by leveraging its synergy with the NEOWISE space mission. With its 15 yr baseline and all-sky mid-IR coverage, NEOWISE provides an excellent avenue to discover thousands of slowly evolving IR outbursts. With its all-sky spectrophotometric coverage and mid-IR sensitivity matching NEOWISE, SPHEREx is uniquely positioned to provide low-resolution IR spectra for the vast majority of these outbursts, several of which are too obscured for ground-based spectroscopic classification. As a demonstration of this approach, we present SPHEREx spectra for eight Galactic transients identified in NEOWISE. This sample includes two previously known FU Orionis-type (FUOr) outbursts whose SPHEREx spectra exhibit clear signatures of cool molecular absorption and three known classical novae showing strong emission lines in SPHEREx. Using these sources as templates, we identify two new FUOrs and one previously missed Galactic nova. Our results highlight the potential of SPHEREx for systematic explorations of the relatively underexplored dynamic IR sky.
SPHEREx as a Frontier for Infrared Transients: Classification of New Galactic FU Ori Outbursts and Classical Novae
Creators
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1.
Columbia University
- 2. Center for Computational Astrophysics, Flatiron Research Institute, 162 5th Avenue, New York, NY 10010, USA
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3.
California Institute of Technology
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4.
Harvard-Smithsonian Center for Astrophysics
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5.
University of Washington
Abstract
Copyright and License
© 2026. 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 are immensely grateful to the SPHEREx team for timely release of SPHEREx data and tools that facilitated this work. We also thank David Hogg for useful discussions. V.R.K. was supported by NASA through the NASA Hubble Fellowship grant #HST-HF2-51578.001-A 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. V.R.K. also acknowledges the hospitality of the CCA-Flatiron Institute. This publication makes use of data products from the Wide-field Infrared Survey Explorer, which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory/California Institute of Technology, funded by the National Aeronautics and Space Administration. This publication makes use of data products from the Spectro-Photometer for the History of the Universe, Epoch of Reionization and Ices Explorer (SPHEREx), which is a joint project of the Jet Propulsion Laboratory and the California Institute of Technology, and is funded by the National Aeronautics and Space Administration. We acknowledge the support of the National Aeronautics and Space Administration through ADAP grant No. 80NSSC24K0663. The computations reported in this Letter were (in part) performed using resources made available by the Flatiron Institute. D.F.’s contribution to this material is based upon work supported by the National Science Foundation under Award No. AST-2401779. J.L.S. acknowledges Columbia Data Science Institute award SF-177. This research award is partially funded by a generous gift of Charles Simonyi to the NSF Division of Astronomical Sciences. The award is made in recognition of significant contributions to Rubin Observatory’s Legacy Survey of Space and Time. The Flatiron Institute is funded by the Simons Foundation. The IRTF data were collected through “Astronomer observing with the Infrared Telescope Facility, which is operated by the University of Hawaii under contract 80HQTR24DA010 with the National Aeronautics and Space Administration”.
Data Availability
This work uses publicly available SPHEREx quick release (QR2) images (SPHEREx Team 2025). The NEOWISE and ATLAS light curves and the SPHEREx and IRTF spectra described here are available on Zenodo at doi:10.5281/zenodo.18762027.
Files
Karambelkar_2026_ApJL_1000_L8.pdf
Additional details
Related works
- Is new version of
- Discussion Paper: arXiv:2602.07129 (arXiv)
- Is supplemented by
- Dataset: 10.5281/zenodo.18762027 (DOI)
Funding
- National Aeronautics and Space Administration
- HST-HF2-51578.001- A
- National Aeronautics and Space Administration
- NAS5-26555
- National Aeronautics and Space Administration
- 80NSSC24K0663
- National Science Foundation
- AST-2401779
- Columbia University
- Columbia Data Science Institute SF-177
- National Aeronautics and Space Administration
- 80HQTR24DA010
Dates
- Submitted
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2026-02-06
- Accepted
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2026-02-25
- Available
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2026-03-11Published
Caltech Custom Metadata
- Caltech groups
- Astronomy Department , Division of Physics, Mathematics and Astronomy (PMA)
- Publication Status
- Published