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Molecular-Line Observations of the Remnant AGB Envelopes Around Planetary Nebulae

Published online by Cambridge University Press:  07 August 2017

R. Sahai
Affiliation:
Chalmers University of Technology, 41296 Gothenburg, Sweden
A. Wootten
Affiliation:
National Radio Astronomy Observatory, Charlottesville, VA 22903, USA
R.E.S. Clegg
Affiliation:
Royal Greenwich Observatory, Madingley Road, Cambridge CB3 OEZ, UK

Abstract

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We present recent results from a “search and mapping” program of molecular line emission (mainly CO) from remnant AGB envelopes around planetary nebulae (PNe), using the SEST (La Silla, Chile). New detections in CO J=2−1 include NGC2899 (0.02K), NGC6369 (0.14K) & NGC7009 (0.08K). In many of the detected PNe, notably NGC3132, IC4406, NGC6302, M1-16, and CPD-56°8032, the molecular envelopes contain 2 kinematically distinct outflows. Mapping of the strongest of these shows (1) that the fast (e.g. Vexp≳40–60 km s−1 in NGC3132, IC4406) outflows have bipolar spatial structure, and (2) there exists an equatorial density enhancement in the slower, more massive [· (Myr−1)>5 10−6(NGC3132), >2 10−5(IC4406)] outflows, which presumably collimates the fast outflow (e.g. Sahai et al. 1990, A & A, 234, L1; Sahai et al. 1992, A & A, 251, 560). The fractional CO abundance in the envelope, f(CO), is probably rather low (<10−4), as a result of photodissociation by the stellar and interstellar UV radiation [e.g. f(CO)≲10−5 in IC4406]. HCN, HCO+, and 13CO have also been detected in several PNe, and sensitive upper limits set on CS, C18O, & C17O (in M1-16), and SO (in NGC3132). Some results are tabulated below, and calculations to estimate the molecular masses, mass-loss rates and molecular abundances are in progress.

Type
III. Highlights on the Nebulae
Copyright
Copyright © Kluwer 1993