Characterizing and spectrally modeling embedded FUor eruptions in the near-infrared

¹ Department of Astronomy, University of Science and Technology of China, Hefei 230026, PR China
² School of Astronomy and Space Sciences, University of Science and Technology of China, Hefei 230026, PR China
³ College of Physics, Guizhou University, Guiyang 550025, PR China

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 29 July 2025
Accepted: 15 April 2026

Abstract

Context. Episodic accretion in young stellar objects (YSOs) is thought to play a critical role in addressing the “luminosity problem” associated with star formation. However, optical surveys tend to be biased against sources that are heavily obscured. Infrared time-domain surveys, such as unTimely WISE, facilitate the identification of such sources within the dense star formation regions of our Galaxy.

Aims. We aim to systematically identify and characterize FUor outbursts in infrared-selected YSOs using high-resolution spectroscopy and detailed disk modeling.

Methods. We conducted follow-up high-resolution spectroscopy with Gemini South/IGRINS for four FUor candidates discovered in infrared time-domain surveys. Using a combination of photometric and spectroscopic observations, we constructed spectral energy distributions and fit them with a disk model that incorporates an actively accreting inner disk together with a passively irradiated outer disk.

Results. All objects show CO and H₂O absorption bands at 2.3 μm, and their positions in the Na + Ca versus CO equivalent width diagram further corroborate their classification as FUors. The best-fitting model spectra closely match both the observed spectral features and the overall continuum, providing additional confirmation of the FUor classification. The best-fit models reveal high extinction values (A_V = 10 − 20 mag), with M_∗Ṁ comparable to those of classical FUors such as FU Orionis. Among the 18 sources initially selected via infrared light curves, 6−7 out of the 8 with available spectra exhibit FUor characteristics, implying a high selection efficiency.