Spectroscopy of quest RR Lyrae variables: The new virgo stellar stream

Abstract

Eighteen RR Lyrae variables (RRLs) that lie in the "12(h).4 clump" identified by the Quasar Equatorial Survey Team ( QUEST) have been observed spectroscopically to measure their radial velocities and metal abundances. Ten blue horizontal branch (BHB) stars identified by the Sloan Digital Sky Survey (SDSS) were added to this sample. Six of the nine stars in the densest region of the clump have a mean radial velocity in the Galactic rest frame (V-gsr) of 99.8 and sigma = km s(-1), which is slightly smaller than the average error of the measurements. The whole sample contains eight RRLs and five BHB stars that have values of V-gsr suggesting membership in this stream. For seven of these RRLs, the measurements of [Fe/H], which have an internal precision of 0.08 dex, yield <[Fe/H]> = -1.86 and sigma = 0.40. These values suggest that the stream is a tidally disrupted dwarf spheroidal galaxy of low luminosity. Photometry from the database of the SDSS indicates that this stream covers at least 106 deg(2) of the sky in the constellation Virgo. The name Virgo stellar stream is suggested.