2005ApJ...620..223L -
Astrophys. J., 620, 223-237 (2005/February-2)
Investigating the possible anomaly between nebular and stellar oxygen abundances in the dwarf irregular galaxy WLM.
LEE H., SKILLMAN E.D. and VENN K.A.
Abstract (from CDS):
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(O/H)=7.83±0.06. This corresponds to [O/H]=-0.83 dex, or 15% of the solar value. In H II regions where [O 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 II 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.
Abstract Copyright:
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Journal keyword(s):
Galaxies: Abundances - Galaxies: Dwarf - Galaxies: Evolution - Galaxies: Individual: Alphanumeric: WLM - Galaxies: Irregular
Nomenclature:
Table 3: [HM95] WLM NNWW (Nos 16NW, 16SE) added, [HM95] WLM NNa (Nos 18a, 18b) added.
CDS comments:
Stars WLM 15, 30 and 31 are [SC85b] 15, ...30, ...31
Simbad objects:
28
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