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J/A+A/604/A41 ESO452-SC11 Stellar parameters and abundances (Koch+, 2017)
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Beginning of ReadMe :J/A+A/604/A41 ESO452-SC11 Stellar parameters and abundances (Koch+, 2017)
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Spectroscopic study of the elusive globular cluster ESO452-SC11 and its
surroundings.
Koch A., Hansen C.J., Kunder A.M.
<Astron. Astrophys. 604, A41 (2017)>
=2017A&A...604A..41K (SIMBAD/NED BibCode)
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ADC_Keywords: Clusters, globular ; Radial velocities ; Abundances
Keywords: stars: abundances - Galaxy: abundances - Galaxy: structure -
globular clusters: individual: ESO452-SC11 - Galaxy: disk -
Galaxy: bulge
Abstract:
Globular clusters (GCs) have long been recognized as being amongst the
oldest objects in the Galaxy. As such, they have the potential of
playing a pivotal role in deciphering the Milky Way's early history.
Here we present the first spectroscopic study of the low-mass system
ESO452-SC11 using the AAOmega multifibre spectrograph at medium
resolution. Given the stellar sparsity of this object and the high
degree of foreground contamination due to its location toward the
Galactic bulge, very few details are known for this cluster - there
is no consensus, for instance, about its age, metallicity, or its
association with the disk or bulge. We identify five member candidates
based on common radial velocity, calcium-triplet metallicity, and
position within the GC. Using spectral synthesis, the measurement of
accurate Fe-abundances from Fe-lines, and abundances of several
alpha-, Fe-peak, and neutron-capture elements (Si, Ca, Ti,Cr, Co,
Ni, Sr, and Eu) is carried out, albeit with large uncertainties. We
find that two of the five cluster candidates are likely non-members,
as they have deviating iron abundances and [alpha/Fe] ratios. The
cluster mean heliocentric velocity is 19+/-2km/s with a velocity
dispersion of 2.8+/-3.4km/s, a low value in line with its sparse
nature and low mass. The mean Fe-abundance from spectral fitting is
-0.88+/-0.03dex, where the spread is driven by observational errors.
Furthermore, the alpha-elements of the GC candidates are marginally
lower than expected for the bulge at similar metallicities. As spectra
of hundreds of stars were collected in a 2-degree field centered on
ESO452-SC11, a detailed abundance study of the surrounding field was
also enabled. The majority of the non-members have slightly higher
[Fe] ratios, in line with the typical nearby bulge population. A
subset of the spectra with measured Fe-peak abundance ratios shows a
large scatter around solar values, albeit with large uncertainties.
Furthermore, our study provides the first systematic measurements of
strontium abundances in a Galactic bulge GC. Here, the Eu and Sr
abundances of the GC candidates are broadly consistent with a disk or
bulge association. Recent proper motions and our orbital calculations
place ESO452 on an elliptical orbit in the central 3kpc of the Milky
Way, establishing a firm connection with the bulge. Finally, while the
radial velocities and preferential position of a dozen of stars
outside the GC radius appear to imply the presence of extra-tidal
stars, their significantly different chemical composition refutes this
hypothesis.
Description:
All our data were taken on June 08, 2013,with the AAOmega multifibre
spectrograph at the 3.9 m Anglo-Australian Telescope (Siding Spring,
Australia).
Objects:
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RA (2000) DE Designation(s)
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16 39 25.50 -28 23 52.0 ESO452-SC1 = ESO 452-11
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