Two Red Clumps and the X-Shaped Milky Way Bulge

From 2MASS infra-red photometry we find two red clump (RC) populations co-existing in the same fields toward the Galactic bulge at latitudes |b|>5.5 deg., ranging over ~13 degrees in longitude and 20 degrees in latitude. We can only understand the data if these RC peaks simply reflect two stellar populations separated by ~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, which is also inconsistent with a tilted bar, although an underlying bar may be present. The stellar densities in the two RCs changes 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 ~20 +/-4 deg., similar to claims for the tilt of a Galactic bar. The distance between the two RCs decreases towards the Galactic plane; seen edge-on the bulge is X-shaped, resembling some extra-galactic 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 ends of a Galactic bar, each side shaped like a funnel or horn. Alternatively, the X, or double funnel shape, may continue to the Galactic center. This would appear peanut/box shaped from the Solar direction, but X-shaped when viewed tangentially.Comment: Accepted for publication in ApJ, revised following referee comments, 12 pages, 8 figure

Reflections on a native title anthropology field school

Anthropologists play a significant role in the native title system in Australia, especially in undertaking connection research to demonstrate the evidentiary basis of claims. In 2010, recognising the lack of sufficiently qualified anthropologists working in native title, the Australian Government introduced a grants program to attract and retain practitioners. This paper describes a field school in the Northern Territory that was funded through the Native Title Anthropologist Grants Program. Through dialogue and interaction with the Aboriginal community, the organisers aimed to expose and interpret ideas, practices, memories, mythologies, relationships and other aspects of society and culture in the terms required for the demonstration of native title. Both novel and successful, the field school points the way for future training initiatives in native title anthropology. Related identifier: ISBN 9781922102317 (paperback) | ISBN 9781922102300 (ebook : pdf) | Dewey Number 346.940432

The chemical composition of a regular halo globular cluster: NGC 5897

We report for the first time on the chemical composition of the halo cluster NGC 5897 (R=12.5 kpc), based on chemical abundance ratios for 27 alpha-, iron-peak, and neutron-capture elements in seven red giants. From our high-resolution, high signal-to-noise spectra obtained with the Magellan/MIKE spectrograph, we find a mean iron abundance from the neutral species of [Fe/H] = -2.04 +/- 0.01 (stat.) +/- 0.15 (sys.), which is more metal-poor than implied by previous photometric and low-resolution spectroscopic studies. NGC 5897 is alpha-enhanced (to 0.34 +/- 0.01 dex) and shows Fe-peak element ratios typical of other (metal-poor) halo globular clusters (GCs) with no overall, significant abundance spreads in iron nor in any other heavy element. Like other GCs, NGC 5897 shows a clear Na-O anti-correlation, where we find a prominent primordial population of stars with enhanced O abundances and ~Solar Na/Fe ratios, while two stars are Na-rich, providing chemical proof of the presence of multiple populations in this cluster. Comparison of the heavy element abundances with the Solar-scaled values and the metal poor GC M15 from the literature confirms that NGC 5897 has experienced only little contribution from s-process nucleosynthesis. One star of the first generation stands out in that it shows very low La and Eu abundances. Overall, NGC 5897 is a well-behaved GC showing archetypical correlations and element-patterns, with little room for surprises in our data. We suggest that its lower metallicity could explain the unusually long periods of RR Lyr that were found in NGC 5897.Comment: 13 pages, 8 figures, accepted for publication in Astronomy & Astrophysic

A Differential Abundance Analysis of Very Metal-Poor Stars

We have performed a differential, line-by-line, chemical abundance analysis, ultimately relative to the Sun, of nine very metal-poor main sequence halo stars, near [Fe/H]=$-$2 dex. Our abundances range from $-2.66\leq\mathrm{[Fe/H]}\leq-1.40$ dex with conservative uncertainties of 0.07 dex. We find an average [$\alpha$/Fe]$=0.34\pm0.09$ dex, typical of the Milky Way. While our spectroscopic atmosphere parameters provide good agreement with HST parallaxes, there is significant disagreement with temperature and gravity parameters indicated by observed colors and theoretical isochrones. Although a systematic underestimate of the stellar temperature by a few hundred degrees could explain this difference, it is not supported by current effective temperature studies and would create large uncertainties in the abundance determinations. Both 1D and $\langle$3D$\rangle$ hydrodynamical models combined with separate 1D non-LTE effects do not yet account for the atmospheres of real metal-poor MS stars, but a fully 3D non-LTE treatment may be able to explain the ionization imbalance found in this work.Comment: 18 pages, 13 tables, 5 figures, Accepted in Ap

A comprehensive chemical abundance study of the outer halo globular cluster M 75

Context: M 75 is a relatively young Globular Cluster (GC) found at 15 kpc from the Galactic centre at the transition region between the inner and outer Milky Way halos. Aims: Our aims are to perform a comprehensive abundance study of a variety of chemical elements in this GC such as to investigate its chemical enrichment history in terms of early star formation, and to search for any multiple populations. Methods: We have obtained high resolution spectroscopy with the MIKE instrument at the Magellan telescope for 16 red giant stars. Their membership within the GC is confirmed from radial velocity measurements. Our chemical abundance analysis is performed via equivalent width measurements and spectral synthesis, assuming local thermodynamic equilibrium (LTE). Results: We present the first comprehensive abundance study of M 75 to date. The cluster is metal-rich ([Fe/H]=-1.16+/-0.02 dex, [alpha/Fe]=+0.30+/-0.02 dex), and shows a marginal spread in [Fe/H] of 0.07 dex, typical of most GCs of similar luminosity. A moderately extended O-Na anticorrelation is clearly visible, likely showing three generations of stars, formed on a short timescale. Additionally the two most Na-rich stars are also Ba-enhanced by 0.4 and 0.6 dex, respectively, indicative of pollution by lower mass (M ~ 4-5 M_Sun) Asymptotic Giant Branch (AGB) stars. The overall n-capture element pattern is compatible with predominant r-process enrichment, which is rarely the case in GCs of such a high metallicity.Comment: 15 pages, 11 figures, 7 tables, accepted for publication in A&