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

TL;DR

This study identifies and models FUor outbursts in infrared-selected young stellar objects, revealing high extinction and accretion rates consistent with classical FUors, using high-resolution spectroscopy and disk modeling.

Contribution

First systematic infrared spectroscopic characterization and spectral modeling of FUor eruptions in embedded young stellar objects.

Findings

All observed objects show characteristic FUor spectral features.

Best-fit models indicate high extinction and accretion rates similar to classical FUors.

High selection efficiency of FUor candidates from infrared light curves.

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 bias 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 H$_2$O absorption bands at 2.3$\mu$m, 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 $M_*\dot{M}$ comparable to those of classical FUors such as FU Orionis. Among 18 sources initially selected via infrared light curves, $6-$7 out of 8 with available spectra exhibit FUor characteristics, implying a high selection efficiency.