Astronomy Colloquium

The Local Group's dwarf galaxies are near enough for exquisitely detailed, resolved stellar spectroscopy and diverse enough to conduct controlled experiments on dark matter and chemical evolution.  I have collected medium-resolution spectra for thousands of stars in many Local Group dwarf galaxies, including satellites of the Milky Way and M31 as well as field dwarf galaxies.  Innovative techniques applied to these spectra recover velocities precise to a few km/s and detailed abundances precise to 0.1 dex.

Although satellite and field dwarf galaxies are different in many ways, their velocity dispersions show that both types of galaxy pose a serious challenge to cold dark matter.  Both types also obey the same mass-metallicity relation despite the large diversity of star formation histories, detailed abundance ratios, and even metallicity distributions.  I will present one galaxy, Segue 2, in detail because it is the least massive galaxy known.  This data set is even rich enough to address stellar evolution.  I will close with a fascinating puzzle involving a great deal of lithium in red giants, which have no right to have any lithium.