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Context. Dwarf spheroidal (dSph) galaxies are the least luminous, least massive galaxies known. Recently, the number of observed galaxies in this class has greatly increased thanks to large surveys. Determining their properties, such as mass, luminosity and metallicity, provides key information in our understanding of galaxy formation and evolution. Aims. Our aim is to provide as clean and as complete a sample as possible of red giant branch stars that are members of the Hercules dSph galaxy. With this sample we explore the velocity dispersion and the metallicity of the system. Methods. Strömgren photometry and multi-fibre spectroscopy are combined to provide information about the evolutionary state of the stars (via the Strömgren c 1 index) and their radial velocities. Based on this information we have selected a clean sample of red giant branch stars, and show that foreground contamination by Milky Way dwarf stars can greatly distort the results. Results. Our final sample consists of 28 red giant branch stars in the Hercules dSph galaxy. Based on these stars we find a mean photometric metallicity of −2.35 ± 0.31 dex which is consistent with previous studies. We find evidence for an abundance spread. Using those stars for which we have determined radial velocities we find a systemic velocity of 45.20 ± 1.09 km s −1 with a dispersion of 3.72 km s −1 , this is lower than values found in the literature. Furthermore we identify the horizontal branch and estimate the mean magnitude of the horizontal branch of the Hercules dSph galaxy to be V 0 = 21.17 ± 0.05, which corresponds to a distance of 147 +8 −7 kpc. Conclusions. When studying sparsely populated and/or heavily foreground contaminated dSph galaxies it is necessary to include knowledge about the evolutionary stage of the stars. This can be done in several ways. Here we have explored the power of the c 1 index in Strömgren photometry. This index is able to clearly identify red giant branch stars redder than the horizontal branch, enabling a separation of red giant branch dSph stars and foreground dwarf stars. Additionally, this index is also capable of correctly identifying both red and blue horizontal branch stars. We have shown that a proper cleaning of the sample results in a smaller value for the velocity dispersion of the system. This has implications for galaxy properties derived from such velocity dispersions.

We present a new mass estimate for the Hercules dwarf spheroidal galaxy (dSph), based on the revised velocity dispersion obtained by Adén et al. (2009).The removal of a significant foreground contamination using newly acquired Strömgren photometry has resulted in a reduced velocity dispersion. Using this new velocity dispersion of 3.72 ± 0.91 km s −1 , we find a mass of M 300 = 1.9 +1.1 −0.8 × 10 6 M ⊙ within the central 300 pc, which is also the half-light radius, and a mass of M 433 = 3.7 +2.2 −1.6 × 10 6 M ⊙ within the reach of our data to 433 pc, significantly lower than previous estimates. We derive an overall mass-to-light ratio of M 433 /L = 103 +83 −48 [M ⊙ /L ⊙ ]. Our mass estimate calls into question recent claims of a common mass scale for dSph galaxies.Additionally, we find tentative evidence for a velocity gradient in our kinematic data of 16 ± 3 km s −1 kpc −1 , and evidence of an asymmetric extension in the light distribution at ∼ 0.5 kpc. We explore the possibility that these features are due to tidal interactions with the Milky Way. We show that there is a self-consistent model in which Hercules has an assumed tidal radius of r t = 485 pc, an orbital pericentre of r p = 18.5 ± 5 kpc, and a mass within r t of M tid,rt = 5.2 +2.7 −2.7 × 10 6 M ⊙ . Proper motions are required to test this model. Although we cannot exclude

We present an assessment of the barium abundance ratios for red giant member stars in the faint Hercules dwarf spheroidal (dSph) galaxy. Our results are drawn from intermediate-resolution FLAMES/GIRAFFE spectra around the Ba II 6141.71 Å absorption line at low signal-to-noise ratios. For three brighter stars we were able to gain estimates from direct equivalent-width measurements, while for the remaining eight stars only upper limits could be obtained. These results are investigated in a statistical manner and indicate very low Ba abundances of log ε(Ba) < ∼ 0.7 dex (3σ). We discuss various possible systematic biasses, first and foremost, a blend with the Fe I 6141.73 Å-line, but most of those would only lead to even lower abundances. A better match with metal-poor halo and dSph stars can only be reached by including a large uncertainty in the continuum placement. This contrasts with the high dispersions in iron and calcium (in excess of 1 dex) in this galaxy. While the latter spreads are typical of the very low luminosity, dark-matter dominated dSphs, a high level of depletion in heavy elements suggests that chemical enrichment in Hercules was governed by very massive stars, coupled with a very low star formation efficiency. While very low abundances of some heavy elements are also found in individual stars of other dwarf galaxies, this is the first time that a very low Ba abundance is found within an entire dSph over a broad metallicity range.

Aims. Our aims are twofold. First we aim to evaluate the robustness and accuracy of stellar parameters and detailed elemental abundances that can be derived from high-resolution spectroscopic observations of microlensed dwarf and subgiant stars. We then aim to use microlensed dwarf and subgiant stars to investigate the abundance structure and chemical evolution of the Milky Way Bulge. Contrary to the cool giant stars, with their extremely crowded spectra, the dwarf stars are hotter, their spectra are cleaner, and the elemental abundances of the atmospheres of dwarf and subgiant stars are largely untouched by the internal nuclear processes of the star. Methods. We present a detailed elemental abundance analysis of OGLE-2008-BLG-209S, the source star of a new microlensing event towards the Bulge, for which we obtained a high-resolution spectrum with the MIKE spectrograph on the Magellan Clay telescope. We have performed four different analyses of OGLE-2008-BLG-209S. One method is identical to the one used for a large comparison sample of F and G dwarf stars, mainly thin and thick disc stars, in the Solar neighbourhood. We have also re-analysed three previous microlensed dwarf stars OGLE-2006

Context. Dwarf spheroidal galaxies are some of the most metal-poor, and least luminous objects known. Detailed elemental abundance analysis of stars in these faint objects is key to our understanding of star formation and chemical enrichment in the early universe, and may provide useful information on how larger galaxies form. Aims. Our aim is to provide a determination of [Fe/H] and [Ca/H] for confirmed red-giant branch member stars of the Hercules dwarf spheroidal galaxy. Based on this we explore the ages of the prevailing stellar populations in Hercules, and the enrichment history from supernovae. Additionally, we aim to provide a new simple metallicity calibration for Strömgren photometry for metal-poor, red giant branch stars. Methods. High-resolution, multi-fibre spectroscopy and Strömgren photometry are combined to provide as much information on the stars as possible. From this we derive abundances by solving the radiative transfer equations through marcs model atmospheres.Results. We find that the red-giant branch stars of the Hercules dSph galaxy are more metal-poor than estimated in our previous study that was based on photometry alone. From this, we derive a new metallicity calibration for the Strömgren photometry. Additionally, we find an abundance trend such that [Ca/Fe] is higher for more metal-poor stars, and lower for more metal-rich stars, with a spread of about 0.8 dex. The [Ca/Fe] trend suggests an early rapid chemical enrichment through supernovae of type II, followed by a phase of slow star formation dominated by enrichment through supernovae of type Ia. A comparison with isochrones indicates that the red giants in Hercules are older than 10 Gyr.

Context. To study the evolution of Li in the Galaxy it is necessary to observe dwarf or subgiant stars. These are the only long-lived stars whose present-day atmospheric chemical composition reflects their natal Li abundances according to standard models of stellar evolution. Although Li has been extensively studied in the Galactic disk and halo, to date there has only been one uncertain detection of Li in an unevolved bulge star. Aims. Our aim with this study is to provide the first clear detection of Li in the Galactic bulge, based on an analysis of a dwarf star that has largely retained its initial Li abundance. Methods. We performed a detailed elemental abundance analysis of the bulge dwarf star MOA-2010-BLG-285S using a highresolution and high signal-to-noise spectrum obtained with the UVES spectrograph at the VLT when the object was optically magnified during a gravitational microlensing event (visual magnification A ∼ 550 during observation). The Li abundance was determined through synthetic line profile fitting of the 7 Li resonance doublet line at 670.8 nm. The results have been corrected for departures from LTE. Results. MOA-2010-BLG-285S is, at [Fe/H] = −1.23, the most metal-poor dwarf star detected so far in the Galactic bulge. Its old age (12.5 Gyr) and enhanced [α/Fe] ratios agree well with stars in the thick disk at similar metallicities. This star represents the first unambiguous detection of Li in a metal-poor dwarf star in the Galactic bulge. We find an NLTE corrected Li abundance of log (Li) = 2.16, which is consistent with values derived for Galactic disk and halo dwarf stars at similar metallicities and temperatures. Conclusions. Our results show that there are no signs of Li enrichment or production in the Galactic bulge during its earliest phases. Observations of Li in other galaxies (ω Cen) and other components of the Galaxy suggest further that the Spite plateau is universal.