Astronomy and Astrophysics – Astrophysics
Scientific paper
Jan 1981
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1981apj...243..127k&link_type=abstract
Astrophysical Journal, Part 1, vol. 243, Jan. 1, 1981, p. 127-139.
Astronomy and Astrophysics
Astrophysics
127
Abundance, Astronomical Spectroscopy, Emission Spectra, Galactic Structure, Line Spectra, Nebulae, Balmer Series, Giant Stars, H Beta Line, Heavy Elements, Helium, Hydrogen Clouds, Neon, O Stars, Oxygen
Scientific paper
Oxygen, helium, and neon abundances are derived from image-dissector scanner observations of 10 emission-line dwarf galaxies. The n(O)/n(H) ratios range from 0.025 to 0.5 the solar value, with the expected anticorrelation with gas temperature. Assuming that n(Ne++)/n(O++) ≍ n(Ne)/n(O), we find a value of 0.23 for this ratio, which is about 50% higher than the values quoted for Orion and the Magellanic Clouds. The mean ratio of n(He+, He++)/n(H+) is 0.082 ± 0.007 for the five best observed galaxies: we do not detect any correlation of this ratio with the oxygen abundance. Reasons are given to refrain from deriving nitrogen abundances for these galaxies. it seems likely that the underlying continua in these galaxies come predominantly from mixtures of 0-type stars and moderately hot giants and supergiants.
Absolute photographic magnitudes, hydrogen masses, and total masses are derived from UBV photometry and 21 cm H I observations of these galaxies. The ratio of H I mass to total mass increases monotonically with decreasing total mass. However, the Virgo dwarfs A1228 +12 and IC 3453 appear to be abnormally deficient in H I for their total masses. The H I content of each may have been modified by its past environment. A decrease in the n(O)/n(H) ratio with decreasing galaxy mass is confirmed, but the scatter is too large for the functional form of the relation to be defined precisely. The emission-line equivalent width of Hβ decreases with distance for the galaxies in our sample; this effect is probably caused by observational selection.
Davidson Kris
Kinman Thomas D.
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