Spectroscopy of QUEST RR Lyrae Variables: The New Virgo Stellar Stream

Eighteen RR Lyrae variables (RRLs) that lie in the "$12\fh 4$ clump"identified by the QUEST survey have been observed spectroscopically to measuretheir radial velocities and metal abundances. Ten blue horizontal branch (BHB)stars identified by the Sloan Digital Sky Survey (SDSS) were added to thissample. Six of the 9 stars in the densest region of the clump have a meanradial velocity in the galactic rest frame ($V_{\rm gsr}$) of 99.8 and $\sigma$= 17.3 ${\rm km s}^{-1}$, which is slightly smaller than the average error ofthe measurements. The whole sample contains 8 RRLs and 5 BHB stars that havevalues of $V_{\rm gsr}$ suggesting membership in this stream. For 7 of theseRRLs, the measurements of [Fe/H], which have an internal precision of 0.08 dex,yield $<{\rm [Fe/H]}> = -1.86$ and $\sigma$ = 0.40. These values suggest thatthe stream is a tidally disrupted dwarf spheroidal galaxy of low luminosity.Photometry from the database of the SDSS indicates that this stream covers atleast 106 deg$^2$ of the sky in the constellation Virgo. The name Virgo StellarStream is suggested.Comment: Replaced with revised version accepted for publication in ApJ Letters 13 pages 4 figure