We present first results from a program to measure the chemical abundances of a large (N>30) sample of thick disk stars with the principal goal of investigating the formation history of the Galactic thick disk. Our analysis confirms previous studies of O and Mg in the thick disk stars which reported enhancements in excess of the thin disk population. Furthermore, the observations of Si, Ca, Ti, Mn, Co, V, Zn, Al, and Eu all argue that the thick disk population has a distinct chemical history from the thin disk. With the exception of V and Co, the thick disk abundance patterns match or tend towards the values observed for halo stars with [Fe/H]~-1. This suggests that the thick disk stars had a chemical enrichment history similar to the metal-rich halo stars. With the possible exception of Si, the thick disk abundance patterns are in excellent agreement with the chemical abundances observed in the metal-poor bulge stars suggesting the two populations formed from the same gas reservoir at a common epoch. We discuss the implications for the formation of the thick disk, new insights presented for theories of nucleosynthesis, and the impact on interpretations of the abundance patterns of the damped Lya systems at high redshift. [significantly abridged]Comment: 34 pages, 27 embedded figures (including 4 color). Uses Latex2e, emulateapj5.sty, onecolfloat.sty. Extra tables can be downloaded at http://www.ociw.edu/~xavier/Science/Stars/index.html. Accepted to the Astronomical Journal: 7/24/0

We report 25,563 radial velocity measurements for 1359 single-lined stars in the Carney-Latham sample of 1464 stars selected for high proper motion. For 171 of these, we present spectroscopic orbital solutions. We find no obvious difference between the binary characteristics in the halo and the disk populations. The observed frequency is the same, and the period distributions are consistent with the hypothesis that the two sets of binaries were drawn from the same parent population. This suggests that metallicity in general, and radiative opacities in particular, have little influence over the fragmentation process that leads to short-period binaries. All the binaries with periods shorter than 10 days have nearly circular orbits, while the binaries with periods longer than 20 days exhibit a wide range of eccentricities and a median value of 0.37. For the metalpoor high-velocity halo binaries in our sample, the transition from circular to eccentric orbits appears to occur at about 20 days, supporting the conclusion that tidal circularization on the main sequence is important for the oldest binaries in the Galaxy.

We have performed a detailed study of the pulsational and evolutionary characteristics of 133 RR Lyrae stars in the globular cluster NGC 5272 (M3) using highly accurate BVI data taken on five separate epochs. M3 seems to contain no less than $32% of Blazhko stars, and the occurrence and characteristics of the Blazhko effect have been analyzed in detail. We have identified a good number ($14%) of overluminous RR Lyrae stars that are likely in a more advanced evolutionary stage off the zero-age horizontal branch (ZAHB). Physical parameters (i.e., temperature, luminosity, and mass) have been derived from B À V colors and accurate color-temperature calibration, and compared with horizontal-branch evolutionary models and with the requirements of stellar pulsation theory. Additional analysis by means of Fourier decomposition of the V light curves confirms, as expected, that no metallicity spread is present in M3. Evolution off the ZAHB does not affect ½Fe=H determinations, whereas Blazhko stars at low amplitude phase do affect ½Fe=H distributions, as they appear more metal-rich. Absolute magnitudes derived from Fourier coefficients might provide useful average estimates for groups of stars, if applicable, but do not give reliable individual values. Intrinsic colors derived from Fourier coefficients show significant discrepancies with the observed ones, and hence the resulting temperatures and temperature-related parameters are unreliable.