Astronomy and Astrophysics – Astrophysics
Scientific paper
May 1989
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1989apj...340..932t&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 340, May 15, 1989, p. 932-942.
Astronomy and Astrophysics
Astrophysics
31
H I Regions, Hydrogen, Planetary Nebulae, Very Large Array (Vla), Image Processing, Line Spectra, Photodissociation, Radiant Flux Density, Stellar Envelopes
Scientific paper
Neutral hydrogen images of the planetary nebula IC 418 have been made with the Very Large Array. These images show H I emission and absorption in close association with the nebula. Assuming a distance of 1 kpc, the total mass of circumnebular neutral hydrogen is 0.35 + or - 0.05 solar mass. Model fits to the data indicate that the neutral gas falls as a 1/r-squared density distribution, with outflow velocity about 5 km/s less than the expansion rate of the ionized gas. The observations also indicate that there is a region devoid of H I emission between the outer edge of the H II nebula and the inner edge of the H I shell. It is suggested that this gap is comprised of molecular hydrogen and that the surrounding H I shell is produced by photodissociation of H2 by the interstellar radiation field. Physical parameters of the H I gas are derived.
Goss William Miller
Gussie Grant Trevor
Taylor Russ A.
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