期刊
ASTRONOMICAL JOURNAL
卷 124, 期 6, 页码 3241-3254出版社
IOP PUBLISHING LTD
DOI: 10.1086/344482
关键词
galaxies : dwarf; Magellanic Clouds
High-resolution infrared spectra (lambda/Deltalambda = 50,000) have been obtained for 12 red giant members of the Large Magellanic Cloud (LMC) with the Gemini South 8.3 m telescope and Phoenix spectrometer. Two wavelength regions, at 15540 and 23400 Angstrom, were observed. Quantitative chemical abundances of carbon (both C-12 and C-13), nitrogen, and oxygen were derived from molecular lines of CO, CN, and OH, while sodium, scandium, titanium, and iron abundances were obtained from neutral atomic lines. The 12 LMC red giants span a metallicity range from [Fe/H] = -1.1 to [Fe/H] = -0.3. It is found that values for both [Na/Fe] and [Ti/Fe] in the LMC giants fall below their corresponding Galactic values ( at these same [Fe/H] abundances) by about similar to0.1-0.5 dex; this effect is similar to abundance patterns found in the few dwarf spheroidal galaxies with published abundances. The program red giants all show evidence of first dredge-up mixing of material exposed to the CN cycle, that is, low C-12/C-13 ratios and lower C-12 with higher N-14 abundances. The carbon and nitrogen trends are similar to what is observed in samples of Galactic red giants, although the LMC red giants seem to show smaller C-12/C-13 ratios for a given stellar mass. This relatively small difference in the carbon isotope ratios between LMC and Galactic red giants could be due to increased extra mixing in stars of lower metallicity, as suggested previously in the literature. Comparisons of the oxygen-to-iron ratios in the LMC and the Galaxy indicate that the trend of [O/Fe] versus [Fe/H] in the LMC falls about 0.2 dex below the Galactic trend. Such an offset can be modeled as due to an overall lower rate of supernovae per unit mass in the LMC relative to the Galaxy, as well as a slightly lower ratio of supernovae of Type II to supernovae of Type Ia.
作者
我是这篇论文的作者
点击您的名字以认领此论文并将其添加到您的个人资料中。
推荐
暂无数据