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Wolf-Rayet Populations in Dwarf Galaxies

Published online by Cambridge University Press:  03 August 2017

Lindsey F. Smith
Lindsey F. Smith*
Affiliation:
Mount Stromlo and Siding Spring Observatories Australian National University GPO Box 4, Canberra ACT 2601 Australia

Abstract

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The Wolf-Rayet (WR) feature at 4650 A is observed in about 10% of the dwarf galaxies with high surface brightness knots. The intensity of the feature implies the presence of tens to thousands of WR stars. Hbeta fluxes imply correspondingly large numbers of O stars. The easily observed intensity ratio WRbump/Hbeta is a measure of the WR/O star numbers.

The metallicity of dwarf galaxies ranges from Z = Zo/30 to Zo/2, or O/H” = log(O/H)+12 = 7.4 to 8.6. WRbump/Hbeta correlates with O/H′ and O/H″ > 7.9 appears to be a necessary condition for the presence of the WR feature. Giant HII regions in ordinary galaxies extend to higher than solar metallicities and, in extreme cases, WR/O ≈ 1 are implied.

The subtypes present in giant HII regions in nearby galaxies appear to be exclusively late type WN and, occasionally, early type WC. Spectra of most BCD galaxies are compatible with a similar population. However, some high metallicity giant HII regions in large galaxies appear to have stronger NIII4640 relative to HeII4686 than occurs in WN subtypes in the Galaxy and the Magellanic Clouds.

The data needed for more detailed analysis of dwarf galaxy observations is collected.

Type
Session VIII. Inventory and Distribution
Information
Symposium - International Astronomical Union , Volume 143: Wolf–Rayet Stars and Interrelations with other Massive Stars in Galaxies , 1991 , pp. 601 - 612
Copyright
Copyright © Kluwer 1991 

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