Abundances of disk and bulge giants from high-resolution optical spectra
II. O, Mg, Co, and Ti in the bulge sample⋆
1 Lund Observatory, Department of Astronomy and Theoretical Physics, Lund University, Box 43, 221 00 Lund, Sweden
2 Instituto de Astrofísica de Canarias (IAC), 38205 La Laguna, Tenerife, Spain
3 Universidad de La Laguna, Dpto. Astrofísica, 38206 La Laguna, Tenerife, Spain
4 Observatoire de la Côte d’Azur, Boulevard de l’Observatoire, BP 4229, 06304 Nice Cedex 4, France
5 Instituto de Astrofísica, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, 782-0436 Macul, Santiago, Chile
6 Millennium Institute of Astrophysics, Av. Vicuña Mackenna 4860, 782-0436 Macul, Santiago, Chile
Received: 16 June 2016
Accepted: 22 November 2016
Context. Determining elemental abundances of bulge stars can, via chemical evolution modeling, help to understand the formation and evolution of the bulge. Recently there have been claims both for and against the bulge having a different [α/Fe] versus [Fe/H] trend as compared to the local thick disk. This could possibly indicate a faster, or at least different, formation timescale of the bulge as compared to the local thick disk.
Aims. We aim to determine the abundances of oxygen, magnesium, calcium, and titanium in a sample of 46 bulge K giants, 35 of which have been analyzed for oxygen and magnesium in previous works, and compare this sample to homogeneously determined elemental abundances of a local disk sample of 291 K giants.
Methods. We used spectral synthesis to determine both the stellar parameters and elemental abundances of the bulge stars analyzed here. We used the exact same method that we used to analyze the comparison sample of 291 local K giants in Paper I of this series.
Results. Compared to the previous analysis of the 35 stars in our sample, we find lower [Mg/Fe] for [Fe/H] >−0.5, and therefore contradict the conclusion about a declining [O/Mg] for increasing [Fe/H]. We instead see a constant [O/Mg] over all the observed [Fe/H] in the bulge. Furthermore, we find no evidence for a different behavior of the alpha-iron trends in the bulge as compared to the local thick disk from our two samples.
Key words: Galaxy: bulge / Galaxy: evolution / stars: abundances
© ESO, 2017