Abundances of carbon and nitrogen in I Zw 18

Journal Article · Thu Sep 01 04:00:00 EDT 1988 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/166690· OSTI ID:6594440

Dufour, R J; Garnett, D R; Shields, G A

The first measurements of the semiforbidden C III 1909 A and forbidden N II 6583 A emission lines in I Zw 18 are reported. These data are combined with previously published spectrophotometry in order to derive the carbon and nitrogen abundances in I Zw 18 with the aid of a nebular model. The CNO abundances in I Zw 18 are found to exceed those found in the Magellanic Clouds and other well-observed oxygen-poor irregular galaxies and are more similar to those in the sun and nearby Galactic H II regions. It is argued that I Zw 18 may be older and more chemically evolved than previously believed, and that its extremely low O/H results from escape of O-rich supernova ejecta from the Galaxy or from dilution by accretion of primordial gas. Alternatively, I Zw 18 may have formed from a preenriched intergalactic medium. Spectroscopic diagnostics for composite photoionization models to fit the spectrum of I Zw 18 are discussed. 35 references.

• Research Organization: Rice Univ., Houston, TX (USA); McDonald Observatory, Austin, TX (USA)
• OSTI ID: 6594440
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 332; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640105* -- Astrophysics & Cosmology-- Galaxies
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ABUNDANCE
CARBON
CHEMICAL COMPOSITION
COMPARATIVE EVALUATIONS
COSMIC GASES
COSMIC RADIO SOURCES
ELEMENTS
EMISSION SPECTRA
ERUPTIVE VARIABLE STARS
FLUIDS
GALACTIC EVOLUTION
GALAXIES
GASES
H2 REGIONS
IONIZATION
NITROGEN
NONMETALS
OXYGEN
PHOTOIONIZATION
SPECTRA
SPECTROPHOTOMETRY
STARS
SUPERNOVAE
VARIABLE STARS