Metal-poor stars towards the Galactic bulge - a population potpourri

Abstract

We present a comprehensive chemical abundance analysis of five red giants and two horizontal branch (HB) stars towards the southern Galactic bulge, at (l,b)$\sim$(0${}^{\mathrm{o}}$,-11${}^{\mathrm{o}}$). Based on high-resolution spectroscopy obtained with the Magellan/MIKE spectrograph, we derived up to 23 chemical element abundances and identify a mixed bag of stars, representing various populations in the central regions of the Galaxy. Although cosmological simulations predict that the inner Galaxy was host to the first stars in the Universe, we see no chemical evidence of the ensuing massive supernova explosions: all of our targets exhibit halo-like, solar [Sc/Fe] ratios, which is in contrast to the low values predicted from Population III nucleosynthesis. One of the targets is a CEMP-s star at [Fe/H]=-2.52 dex, and another one is a moderately metal-poor ([Fe/H]=-1.53 dex) CH star with strong enrichment in s-process elements (e.g., [Ba/Fe]=1.35). These individuals provide the first contenders of these classes of stars towards the bulge. Four of the carbon-normal stars exhibit abundance patterns reminiscent of halo star across a metallicity range spanning -2.0 to -2.6 dex, i.e., enhanced $\alpha$-elements and solar Fe-peak and n-capture elements, and the remaining one is a regular metal-rich bulge giant. The position, distance, and radial velocity of one of the metal-poor HB stars coincides with the old trailing arm of the disrupted Sagittarius dwarf galaxy. While their uncertain proper motions prohibit a clear kinematic separation, the stars' abundances and distances suggest that these metal-poor candidates, albeit located towards the bulge, are not of the bulge, but rather inner halo stars on orbits that make them pass through the central regions. Thus, we caution similar claims of detections of metal-poor stars as true habitants of the bulge. (Abridged)

15 pages, 11 figures, accepted for publication in Astronomy & Astrophysics

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• Iron-peak elements Sc, V, Mn, Cu and Zn in Galactic bulge globular clusters
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• Abundance analysis of APOGEE spectra for 58 metal-poor stars from the bulge spheroid
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• Detailed chemical abundance analysis of the thick disk star cluster Gaia 1
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• Galactic Pal-eontology: Abundance Analysis of the Disrupting Globular Cluster Palomar 5
• Four Metal-poor Stars in the Sagittarius Dwarf Spheroidal Galaxy
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• Impact of distance determinations on Galactic structure. II. Old tracers
• VVV Survey of Blue Horizontal-Branch Stars in the Bulge-Halo Transition Region of the Milky Way
• Spectroscopic confirmation of the low-latitude object FSR 1716 as an old globular cluster
• Radial velocities of RR Lyrae stars in and around NGC 6441
• Chemical composition of the outer halo globular cluster Palomar 15
• S-Process Nucleosynthesis in Chemically Peculiar Binaries
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