Astronomy and Astrophysics – Astrophysics
Scientific paper
Apr 1980
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1980a%26a....84..154h&link_type=abstract
Astronomy and Astrophysics, vol. 84, no. 1-2, Apr. 1980, p. 154-166.
Astronomy and Astrophysics
Astrophysics
21
Hot Stars, Interstellar Matter, Nebulae, Spectrum Analysis, Visual Observation, Electron Density (Concentration), Emission Spectra, Hydrogen Ions, Interstellar Gas, Molecular Spectra, O Stars, Wavelengths
Scientific paper
The galactic nebula Sharpless 156 (IC 1470) has been observed at optical wavelengths, with several instruments. The observed ionisation structure is in excellent agreement with the O 7 V spectral type of the exciting star; there is no bubble of shocked gas as would result if a stellar wind was at work. A fraction of the previously observed radio emission has no optical counterpart. The velocity of the ionised gas is in close agreement with that of the molecular lines. Radio recombination lines have a larger width than expected from the Hα velocity field. The electron density has been derived from the [S II] 6717/6731 line intensity ratio taking into account recent corrections by Pradhan. Prominent features of the nebula are a central elongated brightness hole (at both optical and radio frequencies) and a conspicuous north-south and east-west asymmetry in the brightness distribution and in the distribution of electron density, Hα radial velocity, emission line intensity ratios and reddening. A crude model of the nebula is outlined, delineating the positions where dense ionised gas appears to be coating the nearby molecular cloud, and where escaping low-density gas is present. It is suggested that the exciting star is located in such a way that it ionises an extensive fraction of the surface of the molecular cloud.
Heydari-Malayeri Mohammad
Lortet Marie-Claire
Testor Gerard
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