Investigating the possible anomaly between nebular and stellar oxygen abundances in the dwarf irregular galaxy WLM

Henry Lee, Evan D. Skillman, Kim A. Venn

Research output: Contribution to journalArticle

43 Scopus citations

Abstract

We obtained new optical spectra of 13 H II regions in WLM with EFOSC2; oxygen abundances are derived for nine H II regions. The temperature-sensitive [O III] λ4363 emission line was measured in two bright H II regions, HM 7 and HM 9. The direct oxygen abundances for HM 7 and HM 9 are 12 + log (O/H) = 7.72 ± 0.04 and 7.91 ± 0.04, respectively. We adopt a mean oxygen abundance of 12 + log (0/H) = 7.83 ± 0.06. This corresponds to [O/H] = -0.83 dex, or 15% of the solar value. In H II regions where [0 III] λ4363 was not measured, oxygen abundances derived with bright-line methods are in general agreement with direct values of the oxygen abundance to an accuracy of about 0.2 dex. In general, the present measurements show that the H n region oxygen abundances agree with previous values in the literature. The nebular oxygen abundances are marginally consistent with the mean stellar magnesium abundance ([Mg/H] = -0.62). However, there is still a 0.62 dex discrepancy in oxygen abundance between the nebular result and the A-type supergiant star WLM 15 ([O/H] = -0.21). Nonzero reddening values derived from Balmer line ratios were found in H II regions near a second H I peak. There may be a connection between the location of the second H I peak, regions of higher extinction, and the position of WLM 15 on the eastern side of the galaxy.

Original languageEnglish (US)
Pages (from-to)223-237
Number of pages15
JournalAstrophysical Journal
Volume620
Issue number1 I
DOIs
StatePublished - Feb 10 2005

Keywords

  • Galaxies: abundances
  • Galaxies: dwarf
  • Galaxies: evolution galaxies: individual (WLM)
  • Galaxies: irregular

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