The Near-stellar Environment of Class 0 Protostars: A First Look with Near-infrared Spectroscopy
Emily Laos, Thomas P. Greene, Joan Najita, Keivan G. Stassun
Abstract
Abstract We present near-infrared K -band spectra for a sample of seven Class 0 protostars in the Perseus and Orion star-forming regions. We detect Br γ , CO overtone, and H 2 emission, features that probe the near-circumstellar environment of the protostar and reveal evidence of magnetospheric accretion, a hot inner disk atmosphere, and outflows, respectively. Comparing the properties of these features with those of Class I sources from the literature, we find that their Br γ emission and CO emission are generally consistent in strength and velocity width. The Br γ line profiles are broad and centrally peaked, with FWHMs of ∼200 km s −1 and wings extending to ∼300 km s −1 . The line ratios of our H 2 emission features, which are spatially extended for some sources, are consistent with shock excitation and indicate the presence of strong jets or a disk wind. Within our small sample, the frequency of CO band emission (∼67%) is high relative to that of Class I samples (∼15%), indicating that Class 0 sources have high inner disk accretion rates, similar to those of the most actively accreting Class I sources. Collectively, our results suggest that Class 0 sources have similar accretion mechanisms to the more evolved classes, with strong organized stellar magnetic fields established at the earliest observable stage of evolution.