We show that the Galactic bulge and disk share a similar, strong, decline in [O/Mg] ratio with [Mg/H]. The similarity of the [O/Mg] trend in these markedly different populations suggests that the strong decline is due to a metallicity-dependent modulation of the stellar yields from massive stars by mass loss from winds, related to the Wolf-Rayet phenomenon, as proposed by McWilliam & Rich in 2004. We have modified existing models for the chemical evolution of the Galactic bulge and the solar neighborhood with the inclusion of metallicity-dependent oxygen yields from theoretical predictions for massive stars that include mass loss by stellar winds. Our results significantly improve the agreement between predicted and observed [O/Mg] ratios in the bulge and disk above solar metallicity; however, a small zero-point normalization problem remains to be resolved. The zero-point shift indicates that either the semi-empirical yields of Francois et al. obtained in 2004 need adjustment, or that the bulge initial mass function ( IMF) is not quite as flat as found by Ballero et al. in 2007. Our result removes a previous inconsistency between the interpretation of [O/Fe] and [Mg/Fe] ratios in the bulge, and confirms the conclusion that the bulge formed more rapidly than the disk, based on the overabundances of elements produced by massive stars. We also provide an explanation for the long-standing difference between [alpha/Fe] and [O/Fe] trends among disk stars more metal rich than the Sun.

To compare the globular clusters (GCs) associated with the Sagittarius Galaxy (Sgr) we report the results obtained from new high-resolution spectra of red giant stars in Terzan 8 and Arp 2, collected with the Magellan Inamori Kyocera Echelle (MIKE) spectrograph at Las Campanas Observatory. For Ter 8 we find [Fe I/H] = -2.37 +/- 0.04 and [Fe II/H] = -2.30 +/- 0.07, while for Arp 2 [Fe I/H] = -1.77 +/- 0.04 and [Fe II/H] = -1.89 +/- 0.07. Other elements, usually of interest, show the following results. For oxygen, we obtain [O/Fe] = 0.71 +/- 0.17 for Ter 8 and [O/Fe] = 0.21 +/- 0.22 for Arp 2. For the alpha-elements (Mg, Si, Ca, Ti), the mean values are 0 ''.37 +/- 0.14 dex for Ter 8 and 0.31 +/- 0.11 for Arp 2. These values are not too different from the Galactic GCs at a similar [Fe/H] value. Regarding Cu, we find quite underabundant results for both clusters: [Cu/Fe] = -0.96 for Ter 8 and [Cu/Fe] = -0.93 for Arp 2. The heavy s-process elements Ba and Nd show no excesses in Ter 8 and Arp 2. Our only r-process element, Eu, shows an excess of 0.45 dex in Arp 2, based on the only useful line at 6645 angstrom.

Aims. We model the chemical evolution of manganese relative to iron in three different stellar systems: the Solar neighbourhood, the Galactic bulge, and the Sagittarius dwarf spheroidal galaxy, and we compare our results with recent and homogeneous observational data sets.

We report on the abundance analysis of two red giants in the faint Hercules dwarf spheroidal (dSph) galaxy. These stars show a remarkable deficiency in the neutron-capture elements, while the hydrostatic alpha-elements (O, Mg) are strongly enhanced. Our data indicate [Ba/Fe] and [Mg/Fe] abundance ratios of less than or similar to - 2 and similar to + 0.8 dex, respectively, with essentially no detection of other n-capture elements. In contrast to the only other dSph star with similar abundance patterns, Dra 119, which has a very low metallicity at [Fe/H] = -2.95 dex, our objects, at [Fe/H] similar to -2.0 dex, are only moderately metal-poor. The measured ratio of hydrostatic/explosive alpha-elements indicates that high-mass (similar to 35 M-circle dot) Type II supernovae progenitors are the main, if not only, contributors to the enrichment of this galaxy. This suggests that star formation and chemical enrichment in the ultrafaint dSphs proceeds stochastically and inhomogeneously on small scales, or that the IMF was strongly skewed to high-mass stars. The neutron capture deficiencies and the [Co/Fe] and [Cr/Fe] abundance ratios in our stars are similar to those in the extremely low metallicity Galactic halo. This suggests that either our stars are composed mainly of the ejecta from the first, massive, Population III stars ( but at moderately high [Fe/H]), or that SN ejecta in the Hercules galaxy were diluted with similar to 30 times less hydrogen than typical for extreme metal-poor stars.

Context. The evolution of C and O abundances in the Milky Way can impose strong constraints on stellar nucleosynthesis and help in understanding the formation and evolution of our Galaxy.

We present LTE chemical abundances for five red giants and one AGB star in the Galactic globular cluster (GC) M5 based on high-resolution spectroscopy using the Magellan Inamori Kyocera Echelle spectrograph on the Magellan 6.5 m Clay telescope. Our results are based on a line-by-line differential abundance analysis relative to the well-studied red giant Arcturus. The stars in our sample that overlap with existing studies in the literature are consistent with published values for [Fe/H] and agree to within typically 0.04 dex for the alpha-elements. Most deviations can be assigned to varying analysis techniques in the literature. This strengthens our newly established differential GC abundance scale and advocates future use of this method. In particular, we confirm a mean [Fe I/H] of -1.33 +/- 0.03 (stat.) +/- 0.03 (sys.) dex and also reproduce M5's enhancement in the alpha-elements (O, Mg, Si, Ca, Ti) at +0.4 dex, rendering M5 a typical representative of the Galactic halo. Over-ionization of Fe I in the atmospheres of these stars by non-LTE effects is found to be less than 0.07 dex. Five of our six stars show O-Na-Al-Mg abundance patterns consistent with pollution by proton-capture nucleosynthesis products.

We present high-resolution Magellan/MIKE spectroscopy of the brightest star in the ultra-faint dwarf galaxy Leo IV. We measure an iron abundance of [Fe/H] = -3.2, adding to the rapidly growing sample of extremely metal-poor (EMP) stars being identified in Milky Way satellite galaxies. The star is enhanced in the a elements Mg, Ca, and Ti by similar to 0.3 dex, very similar to the typical Milky Way halo abundance pattern. All of the light and iron-peak elements follow the trends established by EMP halo stars, but the neutron-capture elements Ba and Sr are significantly underabundant. These results are quite similar to those found for stars in the ultra-faint dwarfs Ursa Major II, Coma Berenices, Bootes I, and Hercules, suggesting that the chemical evolution of the lowest-luminosity galaxies may be universal. The abundance pattern we observe is consistent with predictions for nucleosynthesis from a Population III supernova explosion. The extremely low metallicity of this star also supports the idea that a significant fraction (similar to 10%) of the stars in the faintest dwarfs have metallicities below [Fe/H] = -3.0.

From Two Micron All Sky Survey infrared photometry, we find two red clump (RC) populations coexisting in fields toward the Galactic bulge at latitudes vertical bar b vertical bar > 5 degrees.5, ranging over similar to 13 degrees in longitude and 20 degrees in latitude. These RC peaks indicate two stellar populations separated by similar to 2.3 kpc; at (l, b) = (+1, -8) the two RCs are located at 6.5 and 8.8 +/- 0.2 kpc. The double-peaked RC is inconsistent with a tilted bar morphology. Most of our fields show the two RCs at roughly constant distance with longitude, also inconsistent with a tilted bar; however, an underlying bar may be present. Stellar densities in the two RCs change dramatically with longitude: on the positive longitude side the foreground RC is dominant, while the background RC dominates negative longitudes. A line connecting the maxima of the foreground and background populations is tilted to the line of sight by similar to 20 degrees +/- 4 degrees, similar to claims for the tilt of a Galactic bar. The distance between the two RCs decreases toward the Galactic plane; seen edge-on the bulge is X-shaped, resembling some extragalactic bulges and the results of N-body simulations. The center of this X is consistent with the distance to the Galactic center, although better agreement would occur if the bulge is 2-3 Gyr younger than 47 Tuc. Our observations may be understood if the two RC populations emanate, nearly tangentially, from the Galactic bar ends, in a funnel shape. Alternatively, the X, or double funnel, may continue to the Galactic center. From the Sun, this would appear peanut/box shaped, but X-shaped when viewed tangentially.

We present Fe, Si, and Ca abundances for 61 giants in Plaut's window (l = -1 degrees, b = -8.degrees 5) and Fe abundances for an additional 31 giants in a second, nearby field (l = 0 degrees, b = -8 degrees) derived from high-resolution (R approximate to 25,000) spectra obtained with the Blanco 4 m telescope and Hydra multifiber spectrograph. The median metallicity of red giant branch (RGB) stars in the Plaut's field is similar to 0.4 dex lower than those in Baade's window, and confirms the presence of an iron abundance gradient along the bulge minor axis. The full metallicity range of our (biased) RGB sample spans -1.5 < [Fe/H] < +0.3, which is similar to that found in other bulge fields. We also derive a photometric metallicity distribution function for RGB stars in the (l = -1 degrees, b = -8.degrees 5) field and find very good agreement with the spectroscopic metallicity distribution. The radial velocity (RV) and dispersion data for the bulge RGB stars are in agreement with previous results of the Bulge Radial Velocity Assay survey, and we find evidence for a decreasing velocity dispersion with increasing [Fe/H]. The [alpha/Fe] enhancement in Plaut field stars is nearly identical to that observed in Baade's window, and suggests that an [alpha/Fe] gradient does not exist between b = -4 degrees and -8 degrees. Additionally, a subset of our sample (23 stars) appears to be foreground red clump stars that are very metal rich, exhibit small metallicity and RV dispersions, and are enhanced in alpha elements. While these stars likely belong to the Galactic inner disk population, they exhibit [alpha/Fe] ratios that are enhanced above the thin and thick disk.