The chemical composition of red giants in 47 Tucanae. I. Fundamental parameters and chemical abundance patterns
Context. The study of chemical abundance patterns in globular clusters is key importance to constraining the different candidates for intracluster pollution of light elements.
Aims: We aim at deriving accurate abundances for a wide range of elements in the globular cluster 47 Tucanae (NGC 104) to add new constraints to the pollution scenarios for this particular cluster, expanding the range of previously derived element abundances.
Methods: Using tailored 1D local thermodynamic equilibrium (LTE) atmospheric models, together with a combination of equivalent width measurements, LTE, and NLTE synthesis, we derive stellar parameters and element abundances from high-resolution, high signal-to-noise spectra of 13 red giant stars near the tip of the RGB.
Results: We derive abundances of a total 27 elements (O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Mo, Ru, Ba, La, Ce, Pr, Nd, Eu, Dy). Departures from LTE were taken into account for Na, Al, and Ba. We find a mean [Fe/H] = -0.78 ± 0.07 and [ α/ Fe ] = 0.34 ± 0.03 in good agreement with previous studies. The remaining elements show good agreement with the literature, but including NLTE for Al has a significant impact on the behavior of this key element.
Conclusions: We confirm the presence of an Na-O anti-correlation in 47 Tucanae found by several other works. Our NLTE analysis of Al shifts the [Al/Fe] to lower values, indicating that this may be overestimated in earlier works. No evidence of an intrinsic variation is found in any of the remaining elements.
Astronomy and Astrophysics
- Pub Date:
- December 2014
- globular clusters: individual: 47 Tucanae;
- stars: abundances;
- stars: fundamental parameters;
- methods: observational;
- techniques: spectroscopic;
- Astrophysics - Solar and Stellar Astrophysics
- 22 pages, 16 figures. Accepted for publication in A&