CO Emission and Absorption toward V1647 Orionis (McNeil's Nebula)

We present high-resolution infrared spectra of V1647 Ori, the illuminating star of McNeil's Nebula, which reveal the presence of hot and cold gas-phase CO and ices of CO and H₂O. The emission lines of ¹²CO (1-0), (2-1), and (3-2) likely originate from ~2500 K gas in an inner accretion disk region, where substantial clearing of dust has occurred. The width of the emission lines increases with increasing J-value, suggesting that the hottest CO gas we detect is located closest to the central star. The narrower widths of the low-J CO emission lines are indicative of more distant, cooler material in the inner disk. Superposed on the low-J emission lines are narrow ¹²CO absorption components, which are typical of cold interstellar cloud material at a temperature of ~18 K. The very low column density and very cold temperature for the absorbing gas suggest that we are viewing the central star through intervening material within the L1630 cloud and that the disk is oriented nearly face-on. The Doppler shift of the cold CO is offset from the hot gas by 6 ± 2 km s^-1, so it is likely that the very cold CO originates in a foreground cloud rather than the circumstellar material surrounding V1647 Ori. Model fits to the strong H₂O and CO ice absorption bands are consistent with cold (<20 K) amorphous water ice (τ = 0.65) and predominantly apolar CO ice (τ = 0.58). The CO and H₂O ices are unprocessed (unannealed), similar to the ices in dense clouds.