High Resolution Near-Infrared Spectroscopy of FUors and FUor-like stars

We present new high resolution (R ≃ 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 flows. Spectra are presented for the region λ = 2.203 – 2.236 μm 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 μm region are also presented, with the 2.2935 μm v=2–0 CO absorption bandhead being clearly the strongest feature seen in the spectra all FUors and Fuor-like stars. A cross-correlation analysis shows that FUor and FUor-like spectra in the 2.203 – 2.236 μm region are not consistent with late-type dwarfs, giants, nor embedded protostars. The cross-correlations also show that the observed FUor-like Herbig-Haro 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. Subject headings: accretion disks — stars: pre-main-sequence, formation — infrared: stars — techniques: spectroscopic NASA Ames Research Center, M.S. 245-6, Moffett Field, CA 94035-1000 Visiting Astronomer at the Infrared Telescope Facility which is operated by the University of Hawaii under contract to the National Aeronautics and Space Administration. Institute for Astronomy, University of Hawaii, 640 N. A‘ohoku Place, Hilo, HI 96720