科研之友
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摘要
Context. Globular clusters associated with the Galactic bulge are important tracers of stellar populations in the inner Galaxy. High resolution analysis of stars in these clusters allows us to characterize them in terms of kinematics, metallicity, and individual abundances, and to compare these fingerprints with those characterizing field populations. Aims. We present iron and element ratios for seven red giant stars in the globular cluster NGC 6723, based on high resolution spectroscopy. Methods. High resolution spectra (R similar to 48 000) of seven K giants belonging to NGC 6723 were obtained with the FEROS spectrograph at the MPG/ESO 2.2 m telescope. Photospheric parameters were derived from similar to 130 Fe I and Fe II transitions. Abundance ratios were obtained from line-to-line spectrum synthesis calculations on clean selected features. Results. An intermediate metallicity of [Fe/H] = -0.98 +/- 0.08 dex and a heliocentric radial velocity of v(hel) = -96.6 +/- 1.3 km s(-1) were found for NGC 6723. Alpha-element abundances present enhancements of [O/Fe] = 0.29 +/- 0.18 dex, [Mg/Fe] = 0.23 +/- 0.10 dex, [Si/Fe] = 0.36 +/- 0.05 dex, and [Ca/Fe] = 0.30 +/- 0.07 dex. Similar overabundance is found for the iron-peak Ti with [Ti/Fe] = 0.24 +/- 0.09 dex. Odd-Z elements Na and Al present abundances of [Na/Fe] = 0.00 +/- 0.21 dex and [Al/Fe] = 0.31 +/- 0.21 dex, respectively. Finally, the s-element Ba is also enhanced by [Ba/Fe] = 0.22 +/- 0.21 dex. Conclusions. The enhancement levels of NGC 6723 are comparable to those of other metal-intermediate bulge globular clusters. In turn, these enhancement levels are compatible with the abundance profiles displayed by bulge field stars at that metallicity. This hints at a possible similar chemical evolution with globular clusters and the metal-poor of the bulge going through an early prompt chemical enrichment.
- 出版日期2016-3
