The circumstellar and nebular environment of the Becklin-Neugebauer object - 2-5 micron wavelength spectroscopy

Abstract

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 H<SUB>2</SUB> (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<SUB>e</SUB> ≈ 1.3×10<SUP>7</SUP>cm<SUP>-3</SUP> at 20 AU; (2) a highly confined region of excited molecular gas with n<SUB>H2</SUB> ≡ 10<SUP>12</SUP>cm<SUP>-3</SUP> and T ≈ 3500K; (3) a circumstellar envelope with n<SUB>H2</SUB> ≈ 10<SUP>7</SUP>cm<SUP>-3</SUP> 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.