[HTML][HTML] The peculiar Na-O anticorrelation of the bulge globular cluster NGC 6440

C Mu�oz, S Villanova, D Geisler, I Saviane…�- Astronomy &�…, 2017 - aanda.org
C Mu�oz, S Villanova, D Geisler, I Saviane, B Dias, RE Cohen, F Mauro
Astronomy & Astrophysics, 2017aanda.org
Context. Galactic globular clusters (GCs) are essential tools for understanding the earliest
epoch of the Milky Way, since they are among the oldest objects in the Universe and can be
used to trace its formation and evolution. Current studies using high-resolution spectroscopy
for many stars in each of a large sample of GCs allow us to develop a detailed observational
picture of their formation and their relation with the Galaxy. However, it is necessary to
complete this picture by including GCs that belong to all major Galactic components�…
Context
Galactic globular clusters (GCs) are essential tools for understanding the earliest epoch of the Milky Way, since they are among the oldest objects in the Universe and can be used to trace its formation and evolution. Current studies using high-resolution spectroscopy for many stars in each of a large sample of GCs allow us to develop a detailed observational picture of their formation and their relation with the Galaxy. However, it is necessary to complete this picture by including GCs that belong to all major Galactic components, including the bulge.
Aims
Our aim is to perform a detailed chemical analysis of the bulge GC NGC 6440 in order to determine if this object has multiple populations (MPs) and investigate its relation with the bulge of the Milky Way and with the other Galactic GCs, especially those associated with the bulge, which are largely poorly studied.
Methods
We determined the stellar parameters and the chemical abundances of light elements (Na, Al), iron-peak elements (Fe, Sc, Mn, Co, Ni), α-elements (O, Mg, Si, Ca, Ti) and heavy elements (Ba, Eu) in seven red giant members of NGC 6440 using high-resolution spectroscopy from FLAMES-UVES.
Results
We found a mean iron content of [Fe/H] =−0.50 � 0.03 dex in agreement with other studies. We found no internal iron spread. On the other hand, Na and Al show a significant intrinsic spread, but the cluster has no significant O-Na anticorrelation nor does it exhibit a Mg-Al anticorrelation. The α-elements show good agreement with the bulge field star trend, although they are at the high alpha end and are also higher than those of other GCs of comparable metallicity. The heavy elements are dominated by the r-process, indicating a strong contribution by SNeII. The chemical analysis suggests an origin similar to that of the bulge field stars.
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