The Outer Regions of the Galactic Bulge:I Observations

TL;DR

This paper presents an extensive spectroscopic survey of stars in the Galactic bulge, providing new data on stellar velocities and metallicities, and reports the discovery of the Sagittarius dwarf galaxy.

Contribution

It offers the largest spectroscopic dataset for the Galactic bulge to date and introduces optimized methods for star selection and classification.

Findings

Discovery of the Sagittarius dwarf galaxy.

Largest dataset of stellar spectra in the bulge.

Quantified stellar velocity and metallicity measurements.

Abstract

An observational survey of stars selected from the region of sky in the direction of the Galactic bulge is presented. We discuss the choice of tracer populations for this study. Digitised UK Schmidt plate photometry, calibrated with CCD photometry, is obtained in 18 regions over the bulge. Stars are selected for spectroscopic follow-up from within a carefully chosen colour-magnitude selection window, optimised for efficient detection of bulge K giants. Some 1500 stellar spectra were obtained, with the AAT AUTOFIB facility, giving the largest data set yet obtained in this region of the Galaxy, by a factor of $\approx 10$. We have derived a radial velocity and metallicity for each star, and have quantified the uncertainties in these measurements. Luminosity classification has been derived both by visual classification and using an automated routine based on Principal Component Analysis. There are two basic results from this survey: the discovery of the Sagittarius dwarf galaxy, which is described by Ibata, Gilmore & Irwin (1994,1995), and a study of the Galactic Bulge, which is presented in an accompanying paper (Ibata & Gilmore 1995).