Alpha element abundances and gradients in the Milky Way bulge from FLAMES-GIRAFFE spectra of 650 K giants

By O. Gonzalez, M. Rejkuba, M. Zoccali, V. Hill, G. Battaglia, C. Babusiaux, D. Minniti, B. Barbuy, A. Alves-Brito, A. Renzini and 2 more. 2011

135 citations recorded by the source corpus.

Aims. We present the analysis of the [α/Fe] abundance ratios for a large number of stars at several locations in the Milky Way bulge with the aim of constraining its formation scenario. Methods. We obtained FLAMES-GIRAFFE spectra (R = 22 500) at the ESO Very Large Telescope for 650 bulge red giant branch (RGB) stars and performed spectral synthesis to measure Mg, Ca, Ti, and Si abundances. This sample is composed of 474 giant stars observed in 3 fields along the minor axis of the Galactic bulge and at latitudes b = −4 ◦ , b = −6 ◦ , b = −12 ◦ . Another 176 stars belong to a field containing the globular cluster NGC 6553, located at b = −3 ◦ and 5 ◦ away from the other three fields along the major axis. Stellar parameters and metallicities for these stars were presented in Zoccali et al. (2008, A&A, 486, 177). We have also re-derived stellar parameters and abundances for the sample of thick and thin disk red giants analyzed in Alves-Brito et al. (2010, A&A, 513, A35). Therefore using a homogeneous abundance database for the bulge, thick and thin disk, we have performed a differential analysis minimizing systematic errors, to compare the formation scenarios of these Galactic components. Results. Our results confirm, with large number statistics, the chemical similarity between the Galactic bulge and thick disk, which are both enhanced in alpha elements when compared to the thin disk. In the same context, we analyze [α/Fe] vs. [Fe/H] trends across different bulge regions. The most metal rich stars, showing low [α/Fe] ratios at b = −4 ◦ disappear at higher Galactic latitudes in agreement with the observed metallicity gradient in the bulge. Metal-poor stars ([Fe/H] < −0.2) show a remarkable homogeneity at different bulge locations. Conclusions. We have obtained further constrains for the formation scenario of the Galactic bulge. A metal-poor component chemically indistinguishable from the thick disk hints for a fast and early formation for both the bulge and the thick disk. Such a component shows no variation, neither in abundances nor kinematics, among different bulge regions. A metal-rich component showing low [α/Fe] similar to those of the thin disk disappears at larger latitudes. This allows us to trace a component formed through fast early mergers (classical bulge) and a disk/bar component formed on a more extended timescale.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/492528927494f9b85456b7897e5b1c07721fe235

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Citations in the corpus

Chemodynamics of the Milky Way - I. The first year of APOGEE data (2013, result): “…et al. (2007), are somewhat different from the more recent homogeneous abundance analyses of Meléndez et al. (2008), Alves-Brito et al. (2010)20 and Gonzalez et al. (2011) who find a similar abundance pattern for bulge and thick disc giants for [Fe/H]< −0.2, and need to be confirmed or dismissed…”
Stellar populations in the Milky Way bulge region: towards solving the Galactic bulge and bar shapes using 2MASS data (2011, methodology): “Zoccali et al. (2008) studied the MDF and radial velocity distribution from the RGB, Gonzalez et al. (2011) completed the data with the abundances of alpha abundances, Babusiaux et al (2010) studied the correlation between metallicity and kinematics and Hill et al (2011) computed the MDF from the re”
Reddening and metallicity maps of the Milky Way bulge from VVV and 2MASS II. The complete high resolution extinction map and implications for Galactic bulge studies (2012, methodology): “In Gonzalez et al. (2011a), we studied the bar orientation in the inner regions (b = ±1◦) by measuring the mean RC magnitudes as a function of longitude.”
The metallicity distribution of bulge clump giants in Baade’s window (2011, background): “Our derived [Mg/Fe] trend is also in perfect agreement with the recent work of Gonzalez et al. (2011) based on ∼650 RGB stars at four different locations in the bulge analysed in a very similar fashion to our RC sample.”
The Galaxy in Context: Structural, Kinematic, and Integrated Properties (2016, background): “…disk, the thick disk and bulge are more difficult to disentangle because they share kinematic and abundance characteristics, as observed in red giants (Alves-Brito et al. 2010, Ryde et al. 2010, Gonzalez et al. 2011b, Hill et al. 2011) and microlensed dwarf stars (Bensby et al. 2009, 2013).”