Near-IR CO Overtone Emission in 51 Ophiuchi

We present high spectral resolution observations of CO overtone (Δv = 2) emission from hot gas orbiting the Ae star 51 Oph. Using the NIRSPEC instrument on the Keck Telescope we observed various bandheads at high spectral resolving power (R = 25,000). Modeling of the spectra indicates that the radial distribution of excitation temperatures for the vibrational levels is consistent with the gas being in radiative thermal equilibrium except at the inner edge, where low vibrational bands have higher excitation temperatures. Our model fits the emission line width, which has a significant effect on other fitted parameters. We also confirm earlier findings that the emission is caused by hot gas orbiting close to the star in a turbulent disk that is seen close to edge-on. The 10-4 M⊕ of CO gas that is responsible for most of the emission has an average column density of 7.5 × 1020 cm-2.