Astronomy and Astrophysics – Astrophysics
Scientific paper
1999-01-20
Astronomy and Astrophysics
Astrophysics
14 pages, 2 Figs. To be published in The Third Stromlo Symposium - The Galactic Halo: Bright Stars and Dark Matter, eds B K Gi
Scientific paper
In the first part of this contribution the observed velocity dispersions in Galactic halo dwarf spheroidal (dSph) galaxies are reviewed, and the consequences for dark matter content outlined. The results are suggestive of a dSph dark matter mass of ~2x10^7 solar masses, independent of the luminosity of the dSph. Alternatives to the dark matter interpretation are also briefly discussed. In the second part of the contribution the emphasis is on the stellar populations of Galactic dSphs. Recent results for the ages of the oldest populations are presented. These data, together with similar recent results for Galactic halo and LMC globular clusters, indicate that regardless of the subsequent star formation history, the initial epoch of star formation was well synchronized throughout the entire proto-Galactic halo. The implications of the first high dispersion studies of element abundance ratios in Galactic dSph red giants are also discussed. For the Sagittarius dSph in particular, the observed abundance ratios show good agreement with expectations for an episodic star formation history, and such a history is in fact deduced from colour-magnitude diagrams studies.
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