Chemical Abundances in the Stellar Populations of the Leo I and Leo II dSph Galaxies
Chemical Abundances in the Stellar Populations of the Leo I and Leo II dSph Galaxies
复制标题
狮子座 I 和狮子座 II dSph 星系恒星族群中的化学丰度
DOI：
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发表时间：
2002
期刊：
影响因子：
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通讯作者：
P. Stetson
中科院分区：
文献类型：
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作者：
T. Bosler;T. Smecker;P. Stetson
We have obtained calcium abundances and radial velocities f or 102 red giant branch (RGB) stars in the Leo I dwarf spheroidal galaxy (dSph) and 74 RGB st ars in the Leo II dSph using the Low Resolution Spectrograph (LRIS) on the Keck I 10-mete r Telescope. We report on the calcium abundances [Ca/H] derived from the strengths of the Ca II triplet absorption lines at 8498, 8542, 8662̊A in the stellar spectra using a new empirical Ca II triplet ca libr tion to [Ca/H]. The two galaxies have different average [Ca/H] valu es 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 ar 0.10 and 0.17 dex per star. For comparison to existing literature, we also converted ou r 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 approxim ately Gaussian in shape with an excess at the metal-rich end, while that of Leo II show s an abrupt cutoff at the metalrich end. The lower mean metallicity of Leo II is consistent w i h the fact that it has a lower luminosity, hence lower total mass, than Leo I; thus the evol uti n of Leo II may have been affected more by mass lost in galactic winds. Our direct and i ndependent measurement of the metallicity distributions in these dSph will allow a more ac curate star-formation histories to be derived from future analysis of their CMDs.
