Detection of a 63° Cold Stellar Stream in the Sloan Digital Sky Survey

We report on the detection in Sloan Digital Sky Survey data of a 63degree-long tidal stream of stars, extending from Ursa Major to Cancer. Thestream has no obvious association with the orbit of any known cluster orgalaxy. The contrast of the detected stream is greatest when using a star countfilter that is matched to the color-magnitude distribution of stars in M 13,which suggests that the stars making up the stream are old and metal poor. Thevisible portion of the stream is very narrow and about 8.5 kpc above theGalactic disk, suggesting that the progenitor is or was a globular cluster.While the surface density of the stream varies considerably along its length,its path on the sky is very smooth and uniform, showing no evidence ofperturbations by large mass concentrations in the nearby halo. While definitiveconstraints cannot be established without velocity information, the stream'sprojected path and estimates of its distance suggest that we are observing thestream near the perigalacticon of its orbit.Comment: 12 pages, 2 figures, accepted for publication in the Astrophysical Journal Letters. Updated to correspond to version accepted by Ap