MOLECULAR SURVIVAL IN EVOLVED PLANETARY NEBULAE: DETECTION OF H{sub 2}CO, c-C{sub 3}H{sub 2}, AND C{sub 2}H IN THE HELIX

Journal Article · Tue Oct 20 00:00:00 EDT 2009 · Astrophysical Journal (Online)

DOI:https://doi.org/10.1088/0004-637X/704/2/L108· OSTI ID:21367330

Tenenbaum, E D; Woolf, N J; Ziurys, L M ^[1]

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1. Department of Astronomy and Steward Observatory, University of Arizona, 933 N. Cherry Avenue, Tucson, AZ 85721 (United States)

H{sub 2}CO, c-C{sub 3}H{sub 2}, and C{sub 2}H have been identified in the neutral envelope of the highly evolved planetary nebula (PN), the Helix (also know as NGC 7293). Emission from these species were detected toward a peak position in CO, 372'' east of the central star, using the facilities of the Arizona Radio Observatory (ARO). C{sub 2}H and c-C{sub 3}H{sub 2} were identified on the basis of their 3 mm transitions, measured with the ARO 12 m, while five lines of H{sub 2}CO were observed using the 12 m at 2 and 3 mm and the ARO Submillimeter Telescope at 1 mm. From a radiative transfer analysis of the formaldehyde emission, the molecular material was determined to have a density of n(H{sub 2}) approx3 x 10{sup 5} cm{sup -3}, with a kinetic temperature of T {sub kin} approx20 K. Column densities for C{sub 2}H, H{sub 2}CO, and c-C{sub 3}H{sub 2} of N {sub tot} approx1.4 x 10{sup 13} cm{sup -2}, 1.1 x 10{sup 12} cm{sup -2}, and 3 x 10{sup 11} cm{sup -2}, respectively, were derived, corresponding to fractional abundances relative to H{sub 2} of f (H{sub 2}CO) = 1 x 10{sup -7}, f (c-C{sub 3}H{sub 2}) = 3 x 10{sup -8}, and f (C{sub 2}H) = 1 x 10{sup -6} {sub .} The physical conditions found support the notion that molecules in evolved PNe survive in dense clumps in pressure equilibrium, shielded from photodissociation. The presence of H{sub 2}CO, c-C{sub 3}H{sub 2}, and C{sub 2}H, along with the previously observed species CN, HNC, HCN, and HCO{sup +}, indicates that a relatively complex chemistry can occur in the late stages of PN evolution, despite potentially destructive ultraviolet radiation. These molecules have also been observed in diffuse clouds, suggesting a possible connection between molecular material in evolved PNe and the diffuse ISM.

• OSTI ID: 21367330
• Journal Information: Astrophysical Journal (Online), Vol. 704, Issue 2; Other Information: DOI: 10.1088/0004-637X/704/2/L108; ISSN 1538-4357
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ABUNDANCE
CARBON NITRIDES
DENSITY
FORMALDEHYDE
HYDROCYANIC ACID
HYDROGEN
PHOTOLYSIS
PLANETARY NEBULAE
RADIANT HEAT TRANSFER
STARS
TELESCOPES
ULTRAVIOLET RADIATION
ALDEHYDES
CARBON COMPOUNDS
CHEMICAL REACTIONS
DECOMPOSITION
ELECTROMAGNETIC RADIATION
ELEMENTS
ENERGY TRANSFER
HEAT TRANSFER
HYDROGEN COMPOUNDS
INORGANIC ACIDS
INORGANIC COMPOUNDS
NEBULAE
NITRIDES
NITROGEN COMPOUNDS
NONMETALS
ORGANIC COMPOUNDS
PHOTOCHEMICAL REACTIONS
PHYSICAL PROPERTIES
PNICTIDES
RADIATIONS