Chemical characterization of the inner Galactic bulge:North–South symmetry. Issue 4 (15th May 2018)

• Record Type: Journal Article
• Authors: Nandakumar, G; Ryde, N; Schultheis, M; Thorsbro, B; Jönsson, H; Barklem, P S; Rich, R M; Fragkoudi, F
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 478:Issue 4(2018)
• Page Start: 4374
• Page End: 4389
• Publication Date: 2018-05-15
• Subjects: stars: abundances -- stars: late-type -- Galaxy: bulge; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/sty1255
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: While the number of stars in the Galactic bulge with detailed chemical abundance measurements is increasing rapidly, the inner Galactic bulge ($|b| \lt 2^{\circ }$ ) remains poorly studied, due to heavy interstellar absorption and photometric crowding. We have carried out a high-resolution IR spectroscopic study of 72 M giants in the inner bulge using the CRIRES (ESO/VLT) facility. Our spectra cover the wavelength range of 2.0818–2.1444 $\mu $ m with the resolution of R ∼ 50 000 and have signal-to-noise ratio of 50:100. Our stars are located along the bulge minor axis at l = 0°, b = ±0°, ±1°, ±2°, and +3°. Our sample was analysed in a homogeneous way using the most current K -band line list. We clearly detect a bimodal metallicity distribution function with a metal-rich peak at $\rm \sim +0.3\, dex$ and a metal-poor peak at $\rm \sim -0.5\, dex$ and no stars with [Fe/H] > +0.6 dex. The Galactic Centre field reveals in contrast a mainly metal-rich population with a mean metallicity of $\rm +0.3\, dex$ . We derived [Mg/Fe] and [Si/Fe] abundances that are consistent with trends from the outer bulge. We confirm for the supersolar metallicity stars the decreasing trend in [Mg/Fe] and [Si/Fe] as expected from chemical evolution models. With the caveat of a relatively small sample, we do not find significant differences in the chemical abundances between the Northern and the Southern fields; hence, the evidence is consistent with symmetry in chemistry between North and South.