The chemical abundances of the stellar populations in the Leo I and II dSph galaxies

被引:41
作者
Bosler, Tammy L.
Smecker-Hane, Tammy A.
Stetson, Peter B.
机构
[1] Univ Calif Irvine, Div Astron Sci, Natl Sci Fdn, Irvine, CA 92697 USA
[2] Univ Calif Irvine, Dept Phys & Astron, Irvine, CA 92697 USA
[3] Dominion Astrophys Observ, Herzberg Inst Astrophys, Natl Res Council Canada, Victoria, BC V9E 2E7, Canada
基金
美国国家科学基金会;
关键词
stars : abundances; galaxies : abundances; galaxies : dwarf; galaxies : evolution; galaxies : individual : Leo I dSph; galaxies : individual : Leo II dSph;
D O I
10.1111/j.1365-2966.2007.11792.x
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
We have obtained calcium abundances and radial velocities for 102 red giant branch (RGB) stars in the Leo I dwarf spheroidal galaxy (dSph) and 74 RGB stars in the Leo II dSph using the low-resolution spectrograph (LRIS) on the Keck I 10-m telescope. We report on the calcium abundances [Ca/H] derived from the strengths of the Ca II triplet absorption lines at 8498, 8542 and 8662 angstrom in the stellar spectra using a new empirical Ca II triplet calibration to [Ca/H]. The two galaxies have different average [Ca/H] values of -1.34 +/- 0.02 for Leo I and -1.65 +/- 0.02 for Leo II with intrinsic abundance dispersions of 1.2 and 1.0 dex, respectively. The typical random and total errors in derived abundances are 0.10 and 0.17 dex per star. For comparison to the existing literature, we also converted our Ca II measurements to [Fe/H] on the scale of Carretta and Gratton (1997) though we discuss why this may not be the best determinant of metallicity; Leo I has a mean [Fe/H] = -1.34 and Leo II has a mean [Fe/H] = -1.59. The metallicity distribution function of Leo I is approximately Gaussian in shape with an excess at the metal-rich end, while that of Leo II shows an abrupt cut-off at the metal-rich end. The lower mean metallicity of Leo II is consistent with the fact that it has a lower luminosity, hence lower the total mass than Leo I; thus, the evolution of Leo II may have been affected more by mass lost in galactic winds. Our direct and independent measurement of the metallicity distributions in these dSph will allow a more accurate star-formation histories to be derived from future analysis of their colour-magnitude diagrams(CMDs).
引用
收藏
页码:318 / 338
页数:21
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