Astronomy and Astrophysics – Astronomy
Scientific paper
Feb 1983
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1983prhe.work..255s&link_type=abstract
IN: ESO Workshop in Primordial Helium, Garching, West Germany, February 2, 3, 1983, Proceedings (A83-50030 24-90). Garching, Wes
Astronomy and Astrophysics
Astronomy
4
Abundance, Astronomical Spectroscopy, H Ii Regions, Helium, Visible Spectrum, Galactic Nuclei, Interstellar Extinction, Line Spectra, Nebulae
Scientific paper
Difficulties in determining He abundances of optical spectra of H II regions are discussed. The intrinsic line intensity ration associated with the nebular emission must be extracted, although neutral He does not emit lines. The data from galactic H II regions and extragalactic H II regions are treated differently. The spectrographic slit does not cover the whole nebula in galactic observations, while the slit covers a 500 pc region when extragalactic regions are studied. The Balmer discontinuity gives some indication of the population of hot stars (which cause He ionization), as does the continuum shape, with the accuracy depending on the reddening correction, a factor that may not be equally applicable to nebulae and stars. An exact formulation is developed for calculating the He abundance from the observed intensities of the He line and an H line, and areas for which corrections are needed are indicated.
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