Metallicity distribution of red giants in the Inner Galaxy from near infrared spectra

Abstract

Context. The existence in the Milky Way of either a long thin bar with a half length of 4.5 kpc and a position angle of around 45° with respect to the Sun-Galactic centre line or a bulge+bar complex, thicker and shorter, with a smaller tilt respect to the Sun-GC line, has been a matter of discussion in recent decades. Aims. In this paper, we present low resolution (R = 500) near-infrared spectra for selected and serendipitous sources in six inner in-plane Galactic fields at I = 7°, 12°, 15°, 20°, 26° and 27°, with the aim of analysing the stellar content present in those fields. Methods. From the equivalent widths of the main features of the K band spectra (the NaI, Cal and CO bandheads) we have derived the metallicities of the sources by means of the empirical scale obtained by Ramirez et al. (2000, AJ, 120, 833) and Frogel et al. (2001, AJ, 122, 1896) for luminous red giants. Results. Our results show how the mean metallicity of the sample varies with Galactic longitude. We find two groups of stars, one whose [Fe/H] is similar to the values obtained for the bulge in other studies (Molla et al. 2000, MNRAS, 316, 345; Schultheis et al. 2003, AA Hammersley et al. 2000, MNRAS, 317, L45; Picaud et al. 2003, A&A, 408, 141).