Submillimeter line observations of the proto-planetary nebula CRL 2688

The protoplanetary nebula CRL 2688 with 14-arcsec resolution was observed, and the envelope in CO, (C-13)O, CS, and H(C-13)N was mapped. The submillimeter lines show strong emission from two components of the envelope: a cold, dense, optically thick slow wind and a warm, optically thin fast wind. In the maps, the slow wind appears compact and circularly symmetric. A mass-loss rate in the fast wind of 0.00002 solar mass/yr is estimated, if the wind was continuous. The C-12/C-13 ratio in the fast wind is 5, compared to about 20 in the slow wind. The value in the HCN/CO abundance ratio may be lower in the fast wind than in the slow wind. It is argued that the velocity gradients are not caused by rotation, but rather by asymmetries in the envelope associated with the fast wind.