Molecules in bipolar proto-planetary nebulae

Abstract

Two bipolar proto-planetary nebulae, IRAS16594-4656 and IRAS17150-3224, have been detected in various molecular lines, namely CO, ^{13}CO, HCN and CN, and remain undetected in several other species. CO(J=2-1) and CO(J=3-2) line profiles are compared to new spectra of similar PPN candidates, previously undetected in CO(J=2-1): CPD-53^{o}5736, IRAS17106-3046, IRAS17245-3951 and IRAS17441-2411. CO(J=2-1) maps of IRAS16594-4656 and IRAS17150-3224 show that both PPNe have little separation between blue, centre and red-shifted emission, and also that the CO(J=2-1) emission is of a similar size to the telescope beam. Fractional abundances of all detected molecules (except CO) are calculated using the results of CO line modelling and a simple photodissociation model. For those species not detected, upper limits are derived. Comparisons between these fractional abundances and those of other PPNe show that IRAS16594-4656 and IRAS17150-3224 are quite under-abundant when compared to molecule-rich sources like CRL618, CRL2688 and OH231.8+4.2. As a reason for this deficit, the difference in circumstellar envelope/torus density between the molecule-rich sources and the molecule-poor sources is proposed, and supported by a chemical model which follows the transition of a circumstellar envelope through the AGB phase and into the PPN phase of evolution. The model includes the effects of UV radiation, cosmic rays and also X-rays. Finally, the post-AGB ages of these two objects (200-400 yr) are estimated using CN/HCN and HCN/CO ratios and both ages are found to be in agreement with previous figures cited in the literature, IRAS17150-3224 being the younger of the two PPNe.

Accepted by Astronomy & Astrophysics. 21 pages, 11 figures

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Cited by in corpus (17)

• Extended rotating disks around post-AGB stars
• The WISE View of RV Tauri Stars
• Carbonaceous molecules in the oxygen-rich circumstellar environment of binary post-AGB stars: C_{60} fullerenes and polycyclic aromatic hydrocarbons
• Polycyclic aromatic hydrocarbon processing by cosmic rays
• Carbon chemistry in Galactic Bulge Planetary Nebulae
• Spitzer detection of PAH and silicate features in post-AGB stars and young Planetary Nebulae
• The massive expanding molecular torus in the planetary nebula NGC 6302
• PAH Formation in O-rich Planetary Nebulae
• Optical spectrum of the post-AGB star HD56126 in the region 4010-8790 AA
• Submillimeter polarisation and magnetic field properties in the envelopes of proto-planetary nebulae CRL 618 and OH 231.8+4.2
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• Molecules in the carbon-rich protoplanetary nebula CRL 2688
• Observed relationship between CO2-1 and dust emission during post-AGB phase
• A molecular line survey of a sample of AGB stars and planetary nebulae
• Kinematics and H_2 morphology of the multipolar Post-AGB star IRAS 16594-4656
• Evolution from Spherical AGB Wind to Multipolar Outflow in Pre-Planetary Nebula IRAS 17150-3224
• Warm CO in evolved stars from the THROES catalogue. II. Herschel/PACS spectroscopy of C-rich envelopes