High-resolution near-infrared spectroscopy of FUors and FUor-like stars

We present new high-resolution (R similar or equal to 18,000) near-infrared spectroscopic observations of a sample of classical FU Orionis stars (FUors) and other young stars with FUor characteristics that are sources of Herbig-Haro (HH) flows. Spectra are presented for the region lambda = 2.203-2.236 mu m which is rich in absorption lines sensitive to both effective temperatures and surface gravities of stars. Both FUors and FUor-like stars show numerous broad and weak-unidentified spectral features in this region. Spectra of the 2.280-2.300 mu m region are also presented, with the 2.2935 mu m v = 2-0 CO absorption bandhead being clearly the strongest feature seen in the spectra of all FUors and FUor-like stars. A cross-correlation analysis shows that FUor and FUor- like spectra in the 2.203-2.236 mu m region are not consistent with late-type dwarfs, giants, nor embedded protostars. The cross-correlations also show that the observed FUor- like HH energy sources have spectra that are substantively similar to those of FUors. Both object groups also have similar near-infrared colors. The large line widths and double-peaked nature of the spectra of the FUor- like stars are consistent with the established accretion disk model for FUors, also consistent with their near-infrared colors. It appears that young stars with FUor- like characteristics may be more common than projected from the relatively few known classical FUors.