Scientific Highlights with the SMA

Mapping the Central Region of the PPN CRL 618 at Sub-arcsecond Resolution at 350 GHz

CRL 618 is a nearby (∼900 pc) well-studied pre-planetary nebula (PPN), with two major pairs of collimated optical outflow lobes in the east–west direction, expanding rapidly away from the central star. It has started evolving into a PN at the center, with a compact HII region close to the central star detected in 23 GHz continuum. The figure here shows our 350 GHz continuum maps obtained with the Submillimeter Array toward the central star. The cross marks the central star position. The solid and dashed arrows indicate the outflow axes of the optical lobes on the blueshifted and redshifted sides, respectively. Panel (a) shows the continuum map around the central star at an angular resolution of 0.36"×0.24". Panel (b) shows a zoom-in of the continuum map at the center on top of the 23 GHz map of the HII shell (green contours) adopted from Martin-Pintado et al. (1993). Two components are seen: (1) a compact emission at the center tracing the dense inner part of the HII region and it may trace a fast ionized wind at the base; and (2) an extended thermal dust emission surrounding the HII region, tracing the dense core of the circumstellar envelope. The dense core has a density enhancement in the equatorial plane. It may help collimating the fast ionized wind into a bipolar structure, accounting for the shaping mechanism of the PPN and PN (Lee et al. 2013, ApJ, 770, 153).

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