Blue Horizontal-Branch Stars in the Sloan Digital Sky Survey. I. Sample Selection and Structure in the Galactic Halo

We isolate samples of 733 bright (g 18) high Galactic latitude blue horizontal-branch stars with photometry and spectroscopy in the Sloan Digital Sky Survey (SDSS). Comparison of independent photometric and spectroscopic selection criteria indicates that contamination from F and blue straggler stars is less than 10% for bright stars (g 18), and this is qualitatively confirmed by proper motions based on the USNO-A catalog as first epoch. Analysis of repeated observations shows that the errors in radial velocity are ≈26 km s-1. A relation between absolute magnitude and color is established using the horizontal branches of halo globular clusters observed by SDSS. Bolometric corrections and colors are synthesized in the SDSS filters from model spectra. The redder stars agree well in absolute magnitude with accepted values for RR Lyrae stars. The resulting photometric distances are accurate to about 0.2 mag, with a median of about 25 kpc. Modest clumps in phase space exist and are consistent with the previously reported tidal stream of the Sagittarius dwarf galaxy.