A Survey of Large Molecules toward the Proto–Planetary Nebula CRL 618

Abstract

We present the results of our survey toward the proto-planetary nebula CRL 618 for several large, highly saturated, oxygen-bearing organic molecules of biological importance including acetaldehyde (CH3CHO), acetic acid (CH3COOH), dimethyl ether (CH3OCH3), ethanol (CH3CH2OH), formic acid (HCOOH) and methyl formate (HCOOCH3); large carbon chain molecules including methyl cyanide (CH3CN), methylcyanoacetylene (CH3C3N), cyanoacetylene (HC3N), cyanodiacetylene (HC5N), and C6H; and, finally, smaller molecules including 34SO, SO2, OC34S, and MgNC. No biologically important organic molecules were detected. However, we report the first interferometric detections of CH3CN and vibrationally excited HC3N and HC5N toward this source. The temperature and distribution of CH3CN toward CRL 618 indicates that it is formed in the outer envelope surrounding the ultracompact H II region. Furthermore, the P Cygni line profile and corresponding channel maps of vibrationally excited HC5N support its distribution in the extended envelope expanding radially from the central star. The detection of vibrationally excited HC3N confirmed the temperature structure and column density of HC3N in the inner envelope found by Wyrowski and colleagues. Finally, our observations clearly indicate that CRL 618 is a good source of large carbon chain species but a very poor source for detecting or producing organic species of biological importance.