2004/07/19 by Paul Woods, Paul M. Woods, L. -A. Nyman +6 · 2 citations
Chemistry · Physics and Astronomy · #Astrophysics and Star Formation Studies #Molecular Spectroscopy and Structure #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1051/0004-6361:20034388
published as Astron.Astrophys. 429 (2005) 977-992 · Accepted by Astronomy & Astrophysics. 21 pages, 11 figures
arxiv created 2004/07/19 · openalex publication_date 2005/01/01 · arxiv updated 2009/12/01 · openalex created_date 2020/11/23 · openalex updated_date 2026/08/01
Two bipolar proto-planetary nebulae, IRAS 16594-4656 and IRAS 17150-3224, have been detected in various molecular lines, namely CO, 13CO, HCN and CN, and remain undetected in several other species. CO(–1) and CO(–2) line profiles are compared to new spectra of similar PPN candidates, previously undetected in CO(–1): CPD-53°5736, IRAS 17106-3046, IRAS 17245-3951 and IRAS 17441-2411. CO(–1) maps of IRAS 16594-4656 and IRAS 17150-3224 show that both PPNe have little separation between blue, centre and red-shifted emission, and also that the CO(–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 IRAS 16594-4656 and IRAS 17150-3224 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 ( 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, IRAS 17150-3224 being the younger of the two PPNe.