2010ApJ...715..757G

We present high-resolution, near-infrared NIRSPEC observations of the fundamental rovibrational CO and H⁺₃R(1,0), R(1,1)^ u ^, and Q(1,0) transitions toward three early-type young stars: MWC 1080, MWC 349, and LkHα 101. These observations were performed for the purpose of constraining the physical characteristics of the interstellar material along each line of sight. Toward MWC 1080, we detected strong CO absorption and determined a column density upper limit of 1.4x10¹⁴/cm2 for H⁺₃. We infer that there is very little diffuse material along the line of sight toward MWC 1080 and that the CO absorption is consistent with an origin in the dispersing natal cloud. We detected both cold CO and H⁺₃ toward MWC 349, consistent with a diffuse cloud origin. Similarly, both CO and H⁺₃ were detected toward LkHα 101. Using a recently revised value for the cosmic ray ionization rate, we conclude that the CO absorption is consistent with a dense cloud origin while the H⁺₃ could originate in either the dense or diffuse interstellar medium. We also find no evidence for CO fractionation toward LkHα 101 as reported by Goto et al.