Chemical abundances in the inner 5 kpc of the Galactic disk

¹ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
² ING Telescopes, Apartado de Correos 368, Santa Cruz De La Palma, 38780, Canary Islands, Spain
³ Department of Physics and Astronomy, Macalester College, St. Paul, MN 55101, USA
⁴ The Department of Pure and Applied Physics, The Queen's University of Belfast, Belfast BT7 1NN, North Ireland

Corresponding author: S. J. Smartt, sjs@ast.cam.ac.uk

Received: 2 August 2000
Accepted: 17 November 2000

Abstract

High-resolution, high signal-to-noise spectral data are presented for four young B-type stars lying towards the Galactic Centre. Determination of their atmospheric parameters from their absorption line profiles, and uvby photometric measurement of the continua indicate that they are massive objects lying slightly out of the plane, and were probably born in the disk between 2.5-5 kpc from the Centre. We have carried out a detailed absolute and differential line-by-line abundance analyses of the four stars compared to two stars with very similar atmospheric parameters in the solar neighbourhood. The stars appear to be rich in all the well sampled chemical elements (C, N, Si, Mg, S, Al), except for oxygen. Oxygen abundances derived in the atmospheres of these four stars are very similar to that in the solar neighbourhood. If the photospheric composition of these young stars is reflective of the gaseous ISM in the inner Galaxy, then the values derived for the enhanced metals are in excellent agreement with the extrapolation of the Galactic abundance gradients previously derived by Rolleston et al. (2000) and others. However, the data for oxygen suggests that the inner Galaxy may not be richer than normal in this element, and the physical reasons for such a scenario are unclear.