Volume 564, April 2014
|Number of page(s)||15|
|Section||Galactic structure, stellar clusters and populations|
|Published online||04 April 2014|
The extreme chemistry of multiple stellar populations in the metal-poor globular cluster NGC 4833 ⋆,⋆⋆
1 INAF – Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
2 INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
3 Dept. of Physics and Astronomy, Macquarie University, NSW 2109 Sydney, Australia
4 Monash Centre for Astrophysics, Monash University, School of Mathematical Sciences, Building 28, VIC 3800 Clayton, Melbourne, Australia
5 European Southern Observatory, Alonso de Cordova 3107, Casilla 19001, Vitacura, Santiago, Chile
6 INAF-Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italy
7 Dipartimento di Fisica e Astronomia, Università di Catania, via S. Sofia 78, 95123 Catania, Italy
Received: 23 December 2013
Accepted: 27 January 2014
Our FLAMES survey of Na-O anticorrelation in globular clusters (GCs) is extended to NGC 4833, a metal-poor GC with a long blue tail on the horizontal branch (HB). We present the abundance analysis for a large sample of 78 red giants based on UVES and GIRAFFE spectra acquired at the ESO-VLT. We derived abundances of Na, O, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Ba, La, and Nd. This is the first extensive study of this cluster from high resolution spectroscopy. On the scale of our survey, the metallicity of NGC 4833 is [Fe/H] = −2.015 ± 0.004 ± 0.084 dex (rms = 0.014 dex) from 12 stars observed with UVES, where the first error is from statistics and the second one refers to the systematic effects. The iron abundance in NGC 4833 is homogeneous at better than 6%. On the other hand, the light elements involved in proton-capture reactions at high temperature show the large star-to-star variations observed in almost all GCs studied so far. The Na-O anticorrelation in NGC 4833 is quite extended, as expected from the high temperatures reached by stars on the HB, and NGC 4833 contains a conspicuous fraction of stars with extreme [O/Na] ratios. More striking is the finding that large star-to-star variations are also seen for Mg, which spans a range of more than 0.5 dex in this GC. Depletions in Mg are correlated to the abundances of O and anti-correlated with Na, Al, and Si abundances. This pattern suggests the action of nuclear processing at unusually high temperatures, producing the extreme chemistry observed in the stellar generations of NGC 4833. These extreme changes are also seen in giants of the much more massive GCs M 54 and ω Cen, and our conclusion is that NGC 4833 has probably lost a conspicuous fraction of its original mass due to bulge shocking, as also indicated by its orbit.
Key words: stars: abundances / stars: atmospheres / stars: Population II / globular clusters: general / globular clusters: individual: NGC 4833
Full Tables 2, 6–11 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (126.96.36.199) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/564/A60
© ESO, 2014
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