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 revealthepresenceofhotandcoldgas-phaseCOandicesofCO andH2O.Theemissionlinesof 12CO(1-0),(2-1), and(3-2)likelyoriginatefrom 2500Kgasinaninneraccretiondiskregion,wheresubstantialclearingofdusthas 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 2k m 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 H2 Oa nd CO ice ab- sorption bands are consistent with cold (<20 K) amorphous water ice ( ¼ 0:65) and predominantly apolar CO ice ( ¼ 0:58). The CO and H2O ices are unprocessed (unannealed), similar to the ices in dense clouds. Subject headinggs: infrared: ISM — ISM: individual (McNeil's Nebula) — reflection nebulae