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Nils Ryde. Photo.

Nils Ryde


Nils Ryde. Photo.

Chemical characterization of the inner Galactic bulge : North-South symmetry


  • G. Nandakumar
  • N. Ryde
  • M. Schultheis
  • B. Thorsbro
  • H. Jönsson
  • P. S. Barklem
  • R. M. Rich
  • F. Fragkoudi

Summary, in English

While the number of stars in the Galactic bulge with detailed chemical abundance measurements is increasing rapidly, the inner Galactic bulge (|b| < 2°) 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 μm 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 ~ +0.3 dex and a metal-poor peak at ~ -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 +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.


  • Lund Observatory

Publishing year







Monthly Notices of the Royal Astronomical Society





Document type

Journal article


Oxford University Press


  • Astronomy, Astrophysics and Cosmology


  • Galaxy: bulge
  • Stars: abundances
  • Stars: late-type




  • ISSN: 0035-8711