Published February 1, 2026 | Version Published
Journal Article Open

Multicolor Characterization of Optically Invisible FU Orionis-type Outbursts: Demonstration and Prospects for the WINTER Survey

  • 1. ROR icon Harvard-Smithsonian Center for Astrophysics
  • 2. ROR icon Columbia University
  • 3. ROR icon Flatiron Institute
  • 4. ROR icon California Institute of Technology
  • 5. ROR icon Massachusetts Institute of Technology
  • 6. ROR icon University of Maryland, College Park
  • 7. ROR icon Goddard Space Flight Center

Abstract

Episodic mass accretion is the dominant mechanism for mass assembly in the protostellar phase. Although prior optical time-domain searches have allowed detailed studies of individual outbursts, these searches remain insensitive to the earliest stages of star formation. In this paper, we present the characterization of two FU Orionis (FUor) outbursts identified using the combination of the ground-based, near-infrared Wide-field Infrared Transient Explorer (WINTER) and the space-based, mid-infrared NEOWISE survey. Supplemented with near-infrared spectroscopic follow-up, we show that both objects are bona fide FUor type outbursts based on (i) their proximity to star-forming regions, (ii) large amplitude (2–4 magnitudes) infrared brightening over the last decade, (iii) progenitor colors consistent with embedded (Class I) protostars, and (iv) "mixed-temperature" infrared spectra exhibiting characteristic signatures of cool outer envelopes and a hot inner disk with a wind. While one source, WNTR24-cua, is a known FUor that we independently recover; the second source, WNTR24-egv, is a newly confirmed object. Neither source is detected in contemporaneous ground-based optical imaging, despite flux limits ≳100× fainter than their infrared brightness, demonstrating the capabilities of WINTER to identify heavily obscured young stellar object outbursts. We highlight the capabilities of the Galactic Plane Survey of the recently commissioned WINTER observatory in addressing the poorly understood FUor population with its unique combination of real-time detection capabilities, multicolor sensitivity, weekly cadence, and wide area coverage.

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

WINTER’s construction is made possible by the National Science Foundation under MRI grant No. AST-1828470 with early operations supported by AST-1828470 and early science supported by AST-2206731 and AST-2206730. Significant support for WINTER also comes from the California Institute of Technology, the Caltech Optical Observatories, the Bruno Rossi Fund of the MIT Kavli Institute for Astrophysics and Space Research, the David and Lucille Packard Foundation, and the MIT Department of Physics and School of Science. D.F.’s contribution to this material is based upon work supported by the National Science Foundation under Award No. AST-2401779. 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. Furthermore, we acknowledge the support of the National Aeronautics and Space Administration through ADAP grant No. 80NSSC24K0663. This work is based on observations obtained at the Infrared Telescope Facility, which is operated by the University of Hawai‘i under contract 80HQTR19D0030 with the National Aeronautics and Space Administration. We acknowledge ESA Gaia, DPAC and the Photometric Science Alerts Team (http://gsaweb.ast.cam.ac.uk/alerts). This research made use of hips2fits,13 a service provided by CDS. Any use of generative AI in this manuscript adheres to ethical guidelines for use and acknowledgment of generative AI in academic research. Each author has made a substantial contribution to the work, which has been thoroughly vetted for accuracy, and assumes responsibility for the integrity of their contributions.

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Additional details

Related works

Is new version of
Discussion Paper: arXiv:2509.04560 (arXiv)

Funding

National Science Foundation
AST-1828470
National Science Foundation
AST-2206731
National Science Foundation
AST-2206730
National Science Foundation
AST-2401779
National Aeronautics and Space Administration
80NSSC24K0663

Dates

Submitted
2025-09-04
Accepted
2025-11-20
Available
2026-01-28
Published

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