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) and 437 faint (g > 18)high-Galactic latitude blue horizontal branch stars with photometry andspectroscopy in the Sloan Digital Sky Survey (SDSS). Comparison of independentphotometric and spectroscopic selection criteria indicates that contaminationfrom F and blue-straggler stars is less than 10% for bright stars (g<18) andabout 25% for faint stars (g>18), and this is qualitatively confirmed by propermotions based on the USNO-A catalog as first epoch. Analysis of repeatedobservations shows that the errors in radial velocity are approximately 26km/s. A relation between absolute magnitude and color is established using thehorizontal branches of halo globular clusters observed by SDSS. Bolometriccorrections and colors are synthesized in the SDSS filters from model spectra.The redder stars agree well in absolute magitude with accepted values for RRLyrae stars. The resulting photometric distances are accurate to about 0.2magnitudes, with a median of about 25 kpc. Modest clumps in phase space existand are consistent with the previously reported tidal stream of the Sagittariusdwarf galaxy. The sample is tabulated in electronic form in the online version of thisarticle, or by request to the authors.Comment: 35 pages including 14 figures, 5 in color; submitted to A