摘要：We present a comprehensive chemical abundance analysis of five red giants and two
horizontal branch (HB) stars towards the southern edge of the Galactic bulge, at
(l,
b)
~ (0°,−11°).
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 target 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 α-elements and solar Fe-peak and neutron-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 simulations
of the old trailing arm of the disrupted Sagittarius dwarf galaxy. While their highly
uncertain proper motions prohibit a clear kinematic separation, the stars’ chemical
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.
关键词：stars: abundances;stars: carbon;stars: Population
II;Galaxy: abundances;Galaxy: bulge;Galaxy: halo
