The circumstellar and nebular environment of the Becklin-Neugebauer object : lambda=2-5 micron spectroscopy.

The authors present extensive new spectroscopic observations of the BN source in Orion throughout the atmospheric windows from λ = 2 - 5 μm. These bandpasses include the molecular bands of CO (Δv = 1 and Δv = 2) and H₂ (Δv = 1), the hydrogen recombination lines (Brα, Brγ, Pfβ, Pfγ, and Hu 13 - 19), and previously undetected features due to Na I, Fe II, and CO. Four distinct regimes in the circumstellar and line-of-sight gas can be identified from the data: (1) an ultradense, ionized stellar wind with outer boundary at 20 AU and density n_e ≈ 1.3×10⁷cm^-3 at 20 AU; (2) a highly confined region of excited molecular gas with n_H2 ≡ 10¹²cm^-3 and T ≈ 3500K; (3) a circumstellar envelope with n_H2 ≈ 10⁷cm^-3 and T ≈ 600K; and (4) low-excitation molecular gas at T ≈ 150K lying along the line of sight in OMC-1 and the "plateau" source. Velocity measurements of several newly discovered atomic emission lines and molecular absorption systems confirm the peculiar redshifted velocity of BN compared to the OMC-1 molecular cloud.