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We have detected stellar halo streams in the solar neighborhood using datafrom the 7th public data release of the Sloan Digital Sky Survey (SDSS), whichincludes the directed stellar program SEGUE: Sloan Extension For GalacticUnderstanding and Exploration. In order to derive distances to each star, weused the metallicity-dependent photometric parallax relation from Ivezic et al.(2008) for which we examine and quantify the accuracy. Our final sampleconsists of 22,321 nearby (d < 2 kpc), metal-poor ([Fe/H] < -0.5) main-sequencestars with 6D estimates of position and space velocity. We characterize theorbits of these stars through suitable kinematic proxies for their "effective"integrals of motion, angular momentum, eccentricity, and orbital polar angleand compare the observed distribution to expectations from a smoothdistribution in four [Fe/H] bins. On this basis we identify at least fivesignificant "phase-space overdensities" of stars on very similar orbits in thesolar neighborhood to which we can assign unambiguously peaked [Fe/H]distributions. Three of them have been identified previously, including thehalo stream discovered by Helmi et al. (1999) at a significance level of 12.0.In addition, we find at least two new genuine halo streams, judged by theirkinematics and [Fe/H], at significance levels of 2.9 and 4.8, respectively. Forone stream the stars even show coherence in configuration space, matching aspatial overdensity of stars found by Juric et al. (2008) at (R,z) \approx(9.5,0.8) kpc. Our results demonstrate the practical power of our search methodto detect substructure in the phase-space distribution of nearby stars withoutmaking a-priori assumptions about the detailed form of the gravitationalpotential.

Halo streams in the 7th SDSS data release