CRL 2688 - A post-carbon-star object and probable planetary nebula progenitor

Abstract

Observations are reported for millimeter-wavelength emission toward CRL 2688 from H(C-12)N, H(C-13)N, CS, and HC3N. The similarity of this emission and that from the molecular envelope of the carbon star IRC +10216 establishes, beyond a reasonable doubt, that CRL 2688 is a post-carbon-star object. It appears probable that both of these objects will evolve into planetary nebulae. An evolutionary sequence leading from carbon stars to planetary nebulae is outlined.