OH/IR Stars in the Central Region of the Galaxy

Abstract

OH/IR stars offer a unique opportunity to study the distribution and kinematics of the stellar population in the nuclear region of the Galaxy. Systematic 1612 MHz surveys with the 100m Effelsberg telescope and the VLA have detected these stars as close as a few arcminutes from the Galactic Centre. Their density distribution in the inner 5 kpc follows that of the molecular species: a steep decrease from a maximum at R=5 kpc down to a minimum at 3 kpc and a very sharp peak in the inner 350 pc from the Centre. The similarity in radio characteristics with OH/IR stars in the galactic disk indicates that the stars in the nuclear region are of the same population type: a mix of population I and intermediate disk population stars. Nevertheless there is evidence for a paucity of both very old (10⁹yrs) and very young (10⁷yrs) stars in the inner 350 pc.

The distribution of stars in the inner 1° is flattened with an axial ratio of 2:1. There is clear evidence for rotation of 150 km s⁻¹ deg⁻¹ and the velocity dispersion is also 150 km s⁻¹.