A MOLECULAR LINE SURVEY OF THE CARBON-RICH PROTOPLANETARY NEBULA AFGL 2688 IN THE 3 mm AND 1.3 mm WINDOWS

Abstract

We present a spectral line survey of the proto-planetary nebula AFGL 2688 in the frequency ranges of 71-111 GHz, 157-160 GHz, and 218-267 GHz using the Arizona Radio Observatory 12 m telescope and the Heinrich Hertz Submillimeter Telescope. A total of 143 individual spectral features associated with 32 different molecular species and isotopologues were identified. The molecules C 3 H, CH 3 CN, H 2 CO, H 2 CS, and HCO + were detected for the first time in this object. By comparing the integrated line strengths of different transitions, we are able to determine the rotation temperatures, column densities, and fractional abundances of the detected molecules. The C, O, and N isotopic ratios in AFGL 2688 are compared with those in IRC+10216 and the Sun, and were found to be consistent with stellar nucleosynthesis theory. Through comparisons of molecular line strengths in asymptotic giant branch stars, proto-planetary nebulae, and planetary nebulae, we discuss the evolution in circumstellar chemistry in the late stages of evolution.

New Detections of HNC in Planetary Nebulae: Evolution of the [Hcn]/[Hnc] Ratio

“…for the protoplanetary Calabash Nebula, while in CRL 2688, Zhang et al (2013) found f(HNC/H 2 )∼5.7×10…”

(Sub)mm-Wavelength Observations of Pre-Planetary Nebulae and Young Planetary Nebulae

“…Some examples are the C-rich AGB star IRC+10216 [41,42], probably the best studied AGB star, and the O-rich AGB stars IK Tau and R Dor [43,44]. The chemistries of a number of pPNe are also relatively well characterized, particularly the C-rich pPNe CRL 618 [45] and CRL 2688 [46] and the O-rich source OH 231.8+4.2 [47,48].…”

The spectra of evolved stars at 20--25\,GHz: tracing circumstellar chemistry during the asymptotic giant branch to planetary nebula transition

“…Presented in Figure 6 are the rotational diagrams of the cyanopolyyne molecules detected in CRL 2688. Since the present survey only covers the low energy range and the thermal structure within the CSE is often stratified, data points from previous high-frequency surveys (Zhang et al 2013;Chau et al 2012) have been concatenated with those from the present study for a more reliable estimate of the excitation temperatures and column densities. Results from rotational analysis of cyanopolyyne emission from CRL 2688 and IRC+10216 are presented in Table 4.…”

“…In particular, the survey of Gong et al (2015), which covered the 17.8 -26.3 GHz frequency range, detected a total of 78 transitions from known molecular species, amongst which 23 were detected for the first time outside the solar system. Our research group has been engaged in a long-term project to perform systematic spectral line surveys in a large sample of evolved stars with comprehensive wavelength coverage (He et al 2008;Zhang et al 2008Zhang et al , 2009aChau et al 2012;Zhang et al 2013). In the present paper, we investigate the 20-25 GHz spectra of a sample consisting of C-rich CSEs including IRC+10216, CRL 2688, CRL 618, and NGC 7027. Displayed in Table 1 are the physical properties of the scientific objects consolidated from a series of literature searches.…”

“…A wide variety of molecules -such as the silicon-bearing molecules SiO and SiS, cyanopolyyne chains up to HC 9 N and carbon radicals up to C 6 H -have been detected in CRL 2688 (Lucas et al 1986;Truong-Bach et al 1993;Bachiller et al 1997a,b). Line surveys of this objects have been recently performed at 1 mm, 1.3 mm, and 3 mm windows (Park et al 2008;Zhang et al 2013). CRL 618 is a more evolved PPN having a central star with a higher effective temperature (3.0 × 10 4 K; Sánchez Contreras & Sahai 2004).…”