Astronomy and Astrophysics – Astronomy
Scientific paper
Apr 1982
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1982apj...255..564d&link_type=abstract
Astrophysical Journal, Part 1, vol. 255, Apr. 15, 1982, p. 564-576.
Astronomy and Astrophysics
Astronomy
26
Early Stars, Emission Spectra, Hydrogen Clouds, Radio Sources (Astronomy), Stellar Spectra, Absorption Spectra, Astronomical Maps, Carbon Monoxide, Centimeter Waves, H Lines, Interstellar Gas, Nebulae, Radio Interferometers, Stellar Envelopes, Synthetic Apertures
Scientific paper
The reflection nebula NGC 1579 is situated in a dark cloud and is illuminated by the highly obscured emission-line star LkHα 101. New aperture synthesis observations at 21 cm (resolution 2' X by 0.67 km s-1 in radial velocity) show a continuum source of 176 mJy centered on the star and ∼85 Msun of atomic hydrogen in a surrounding cloud ∼3.5 pc across at the assumed distance of 800 pc. The highest column densities of H I (13 × 1020 cm-2) are near the stellar position with the greatest extension of low-brightness emission to the northwest. The gas is distributed over radial velocities -4 to 6 km s-1 (LSR) with an absorption component on most profiles near 1 km s-1. The absorption, of optical depth ∼3, may be due to a cool H I shell on the near side of the associated dark cloud.
Models of the H I emission cloud based on two-step dissociation of H2 by ultraviolet radiation from the central star indicate that the density in the medium is much higher on the near side of the star than on the other, in agreement with the observed extended distribution of CO. Unlike H I zones associated with more diffuse H ii regions, no expansion of the atomic gas is detected. This reinforces other evidence that the star and its H ii and H I regions are newly formed.
The widths of the H I emission profiles (∼ km s-1) are more than twice those of CO profiles in the same directions, which indicates that there is no detailed mixing of the CO and the atomic gas.
Dewdney Peter E.
Roger Robert S.
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