High-resolution observations of CO from the bipolar nebula CRL 2688

Abstract

The results of high spatial resolution mapping observations of CO emission from the bipolar nebula CRL 2688 are reported. The CO spectrum toward the center shows line wings with a full width of 85 km/s. On the blueshifted wing, a narrow and deep absorption feature is seen at a velocity shifted by 20 km/s from the systemic velocity. A central compact core elongated perpendicularly to the bipolar axis and blueshifted high-velocity emission distributed along the optical lobes suggest the presence of an expanding disk of molecular gas and fast stellar wind as the acceleration agent. The absorption feature suggests that an expanding cold absorbing envelope surrounds the relatively warm molecular envelope. The absorbing envelope has an excitation temperature lower than about 5 K and an optical depth larger than 1.2 in the CO(J = 1-0) line, and it is expanding at 20 km/s. The size of this envelope is larger than about 0.6 pc and its mass is larger than 0.016-0.044 solar mass. 16 references.