Near-Infrared Spectroscopy of M c Neil's Nebula Object

Abstract

We present 0.8-5.2 μm spectroscopy of the compact source at the base of a variable nebula (McNeil's Nebula Object) in the Lynds 1630 dark cloud that went into outburst in late 2003. The spectrum of this object reveals an extremely red continuum, CO bands at 2.3-2.5 μm in emission, a deep 3.1 μm ice absorption feature, and a solid-state CO absorption feature at 4.7 μm. In addition, emission lines of H, Ca II, Mg I, and Na I are present. The Paschen lines exhibit P Cygni profiles, as do two lines of He I, although the emission features are very weak in the latter. The Brackett lines, however, are seen to be purely in emission. The P Cygni profiles clearly indicate that mass outflow is occurring in a wind with a velocity of ~400 km s-1. The H line ratios do not yield consistent estimates of the reddening, nor do they agree with the extinction estimated from the ice feature (AV ~ 11). We propose that these lines are optically thick and are produced in a dense, ionized wind. The near-infrared spectrum does not appear similar to any known FUor or EXor object. However, all evidence suggests that McNeil's Nebula Object is a heavily embedded low-mass Class I protostar, surrounded by a disk, whose brightening is due to a recent accretion event.