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Session 84 - QSOs and BL Lacs.
Display session, Wednesday, January 17
North Banquet Hall, Convention Center
We report on the discovery of 6 more bright (r < 19.5^m) quasars from the digitized POSS-II (DPOSS). This is a continuation of a project to discover a complete sample of z > 4 quasars, eventually covering the entire high-latitude northern sky, and to use them for a variety of cosmological studies. Our initial efforts have been described by Kennefick et al. (1995, AJ, 110, 78; and AJ in press, Dec'95). The data set consists of all objects classified as stellar on the red survey plates, down to r = 19.6^m (this limit is imposed by the accuracy of star-galaxy classifications, rather than the detectability). There are typically \sim 10^5 stars per sky survey field above that limit, at high to intermediate Galactic latitudes. We use a multicolor method to select quasar candidates, on (g-r) vs. (r-i) color-color diagrams, in a well-defined portion of the color space. Typically we end up with \sim 1 - 10 candidates per survey field, which need to be checked spectroscopically. The follow-up spectroscopy is being obtained at the Palomar 200-inch telescope. Our success rate is on the average one z>4 quasar per \sim 2.5 sky survey fields. DPOSS is thus a very good source of bright, z > 4 quasars. We estimate that up to \sim 300 - 400 quasars at z > 4 will be detected in the DPOSS database. We have also started a search for extremely red stars at high Galactic latitudes using these data.
