RR Lyrae Stars in the Halo: Tracers of Streams of Debris of Disrupted Galaxies

Abstract

We discuss the first part of a survey for RR Lyrae variables in the galactic halo that is being made with the 1m Schmidt telescope at the Venezuelan National Observatory. So far the survey has discovered 497 variables in 380 sq. degrees, lying from 4 to 60 kpc from the Sun. It has detected three statistically significant clumps of variables, which shows that outer halo does not have smooth density contours. One clump is located at 50 kpc from the galactic center, and it is probably tidal debris from the Sagittarius dwarf spheroidal galaxy. A second structure, at 17 kpc from the galactic center, appears to be due to the tidal disruption of the globular cluster Pal 5. The third group, at 19 kpc, is not related with any known globular cluster or dwarf galaxy. The little that is known about its properties is consistent with it being debris from a disrupted galaxy.