Emission-Line Imaging of the ``Classic'' H II Region M42 and the Giant Emission Bubble N70

Details Emission-Line Imaging of the ``Classic'' H II Region M42 and the Giant Emission Bubble N70 Emission-Line Imaging of the ``Classic'' H II Region M42 and the Giant Emission Bubble N70

Dec 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994aas...185.8202p&link_type=abstract

American Astronomical Society, 185th AAS Meeting, #82.02; Bulletin of the American Astronomical Society, Vol. 26, p.1452

Astronomy and Astrophysics

Astronomy

Scientific paper

As part of a larger effort to investigate the line-emitting properties of starburst nebulae, we have undertaken a comparative study of two nearby emission nebulae associated with high-mass star formation. The Orion nebula (M42) is classified as a ``classic'' H ii region. It is approximately 3 pc in size and is powered mostly by EUV photons from the central Trapezium cluster of O and B-type stars. The emission bubble N70, in the Large Magellanic Cloud, is approximately 95 pc in size with a nearly spherical shell-like morphology. The nebular emission is powered by an uncertain combination of EUV photons, intense winds, and supernova blast waves from the central population of high-mass stars. Using the Goddard Fabry-Perot etalons with the Rutgers Fabry-Perot imaging system on the CTIO 1.5-m telescope, we have obtained narrowband images (FWHM ~ 6 Angstroms) of M42 and N70 in the light of Hα lambda 6563, [N ii] lambda 6584, [S ii] lambda lambda 6717,6731, and (for N70) [O iii] lambda 5007, along with the corresponding red and blue continua. In M42, the central 0.5 pc is characterized by low [N ii]/Hα and [S ii]/Hα flux ratios (~ 0.1--0.2 and ~ 0.01--0.03, respectively). Higher flux ratios are evident along the ionization front ([N ii]/Hα ~ 0.4, and [S ii]/Hα ~ 0.06) and in the neighboring Herbig-Haro objects ([N ii]/Hα ~ 0.35, and [S ii]/Hα ~ 0.1). By contrast, N70 shows much higher [S ii]/Hα flux ratios which smoothly increase with radius --- from < 0.3 near the center to > 1.0 towards the outer filamentary shell. These ratios, when combined with generally low [N ii]/Hα flux ratios of < 0.25, are difficult to explain with either pure photon or shock ionization models. EUV photons must contribute a significant fraction of the inner nebula's ionization, because the [O iii] emission shows a strong concentration towards the central hot stars. The contending ionization processes in the outer filaments are evaluated in terms of the available data.

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