Physics
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004phdt........36b&link_type=abstract
Ph.D dissertation, 2004. 259 pages; United States -- California: University of California, Irvine; 2004. Publication Number: AA
Physics
3
Leo I, Dwarf Galaxies, Calcium Ii
Scientific paper
I have correlated the reduced equivalent width of the Ca II near-infrared triplet absorption lines (W ' ) with calcium abundance ([Ca/H]) derived from model atmosphere abundance analysis of neutral calcium lines for red giant branch (RGB) stars in 15 star clusters. The W ' to [Ca/H] calibration is based on observations of stars in open and globular clusters with ages 2 to 16 Gyrs and with -2.0 [Special characters omitted.] [Ca/H] [Special characters omitted.] +0.2 to assure a robust calibration. The relationship between W ' and [Ca/H] is [Ca/H] = -2.778 (+/-0.061) + 0.470 (+/-0.016)W ' . The calibration can be applied to Galactic and extragalactic systems to accurately determine [Ca/H] regardless of their star-formation histories.
As a first application of the calibration, I derived the calcium abundance distribution of the stellar populations of the Leo I and Leo II dwarf spheroidal (dSph) galaxies to constrain the physical processes that regulate their evolution. I observed the strengths of the Ca II triplet lines in 101 RGB stars Leo I and 74 RGB stars in Leo II and have determined the abundances with typical random and total errors of 0.10 and 0.17 dex per star, respectively. The two galaxies have different average abundances, [Ca/H], of -1.34 +/- 0.02 (s = 0.21 dex ) for Leo I and -1.65 +/- 0.02 (s = 0.17 dex ) for Leo II with intrinsic abundance dispersions of 1.2 and 1.0 dex, respectively. The observed dispersion implies that the galaxies have a wider range in stellar ages than previously inferred. Additionally, the shapes of the abundances distributions differ possibly indicating that Leo II had more mass loss in its evolution causing its formation to cease earlier than Leo I.
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