Chemical Compositions of Field and Globular Cluster RR Lyrae Stars. II. ω Centauri

Magurno, D.; Sneden, C.; Bono, G.; Braga, V. F.; Mateo, M.; Persson, S. E.; Preston, G.; Thévenin, F.; da Silva, R.; Dall’Ora, M.; Fabrizio, M.; Ferraro, I.; Fiorentino, G.; Iannicola, G.; Inno, L.; Marengo, M.; Marinoni, S.; Marrese, P. M.; Martínez-Vázquez, C. E.; Matsunaga, N.; Monelli, M.; Neeley, J. R.; Nonino, M.; Walker, A. R.
Referencia bibliográfica

The Astrophysical Journal, Volume 881, Issue 2, article id. 104, 16 pp. (2019).

Fecha de publicación:
8
2019
Número de autores
24
Número de autores del IAC
1
Número de citas
24
Número de citas referidas
23
Descripción
We present a detailed spectroscopic analysis of RR Lyrae (RRL) variables in the globular cluster NGC 5139 (ω Cen). We collected optical (4580–5330 Å), high-resolution (R ∼ 34,000), high signal-to-noise ratio (∼200) spectra for 113 RRLs with the multifiber spectrograph M2FS at the Magellan/Clay Telescope at Las Campanas Observatory. We also analyzed high-resolution (R ∼ 26,000) spectra for 122 RRLs collected with FLAMES/GIRAFFE at the Very Large Telescope, available in the ESO archive. The current sample doubles the literature abundances of cluster and field RRLs in the Milky Way based on high-resolution spectra. Equivalent-width measurements were used to estimate atmospheric parameters, iron, and abundance ratios for α (Mg, Ca, Ti), iron peak (Sc, Cr, Ni, Zn), and s-process (Y) elements. We confirm that ω Cen is a complex cluster, characterized by a large spread in the iron content: ‑2.58 ≤ [Fe/H] ≤ ‑0.85. We estimated the average cluster abundance as < [{Fe}/{{H}}]> =-1.80+/- 0.03, with σ = 0.33 dex. Our findings also suggest that two different RRL populations coexist in the cluster. The former is more metal-poor ([Fe/H] ≲ ‑ 1.5), with almost solar abundance of Y. The latter is less numerous, more metal-rich, and yttrium enhanced ([Y/Fe] ≳ 0.4). This peculiar bimodal enrichment only shows up in the s-process element, and it is not observed among lighter elements, whose [X/Fe] ratios are typical for Galactic globular clusters. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.
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