High spatial resolution observations of HCO(+) in the NGC 7027 molecular envelope

Details High spatial resolution observations of HCO(+) in the NGC 7027 molecular envelope High spatial resolution observations of HCO(+) in the NGC 7027 molecular envelope

Jun 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992apj...392..597d&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 392, no. 2, June 20, 1992, p. 597-601.

Astronomy and Astrophysics

Astrophysics

17

Formyl Ions, Interstellar Matter, Molecular Clouds, Planetary Nebulae, Millimeter Waves, Spatial Resolution, Stellar Envelopes, Ism: Molecules, Planetary Nebulae: Individual (Ngc 7027))

Scientific paper

We present maps of the HCO+ J = 1-0 line in the molecular envelope of the planetary nebula, NGC 7027, with a spatial resolution of 4".5 x 3".2. Emission has been found to arise from a torus of the size of about 15" with an axis oriented to northwest-southeast The HCO+ torus lies at the periphery of the ionized gas of NGC 7027 and is much smaller than the extension of the CO emitting region (70"). Modeling and statistical equilibrium calculations show that the number density of H2 and the HCO+ abundance at the inner boundary are 1.5 × 105 cm-3 and 3 × 10-8 per H2, respectively, and that the HCO+ abundance sharply decreases with radius. The highly asymmetric profile of the observed HCO+ line is due to the absorption by the part of the torus in front of the central continuum source. The concentration of HCO+ emission at the periphery of ionized gas provides a severe constraint to the modeling of the ionization source. A soft X-ray ionization from the hot central star and subsequent ion-molecule reactions are the most plausible mechanisms to produce highly abundant HCO+ in the molecular envelope of NGC 7027.

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