1″ Resolution Mapping of the Molecular Envelope of the Protoplanetary Nebula CRL 618

Abstract

We present 1 00 resolution interferometric maps of the CO J ¼ 2 1a nd HC3N J ¼ 25 24 emission in the protoplanetary nebula CRL 618 obtained with the millimeter array of the Owens Valley Radio Observatory (OVRO). Our CO data trace with high accuracy the spatio-kinematic structure of different molecular components: (1) the fast, bipolar outflow, which is observed up to axial distances of � 2B 5( � 2:7 ; 10 16 cm) from the nebula center with a maximal deprojected expansion velocity of Vexp � 340 km s � 1 ; (2) the roughly round outer halo, which is slowly expanding at Vexp � 17 km s � 1 ; (3) an extended structure that is elongated in the polar direction � 6 00 (� 8:1 ; 10 16 cm),surroundingtheopticallobes,andthatexpandsatVexp � 22kms � 1 (slowaxialcomponent); and(4)a dense, inner torus-likecore (Rout � 1:6 ; 10 16 cm) expanding atVexpP12kms � 1 . Components (3) and (4) have been revealed for the first time by our high angular resolution data. The geometry, kinematics, density, and temperaturedistributionoftheindividualcomponentsofthemolecularenvelopeofCRL618havebeenconstrained by fitting a spatio-kinematic model to the data. We interpret our results in terms of nebular evolution as follows. In the last k2500 yr, there have been at least two distinct episodes of mass loss at a large scale in the form of a slow wind. The firsttookplace at a rate of ˙