THE ASTRONOMICAL JOURNAL      VOLUME 106, NUMBER 2, PAGE 591        AUGUST 1993

   EARLY-TYPE STARS IN ORTHOGONAL HALO FIELDS. I.  AN OBJECTIVE-PRISM SURVEY

                  A. W. RODGERS, W. H. ROBERTS, AND I. WALKER

 Mount Stromlo and Siding Spring Observatories, Institute of Advanced Studies,
Australian National University, Private Bag, Weston Creek Post Office, ACT 2611
                                   Australia
        Electronic mail: alex@merlin.anu.edu.au, bill@merlin.anu.edu.au


                                   ABSTRACT

    The results are reported of an objective-prism survey of stars, mostly
    earlier than spectral type F5, for two fields at (l;b) = (90 deg and
    270 deg; -45 deg).  The fields, each of approximately 70 square
    degrees, are examined on plates taken with the Schmidt Telescope of the
    Anglo-Australian Observatory.  The brightness range of the stars
    classified is 10 < V < 15.  The prism combination used provides a
    dispersion of 600 A/mm at Hgamma.  The spectral classification
    presented is defined by the equality of equivalent widths of Ca II K
    and Hdelta at type "F0" and the absence of Ca II K in stars with
    significant Balmer lines at type "A0".  Positions listed in the catalog
    were measured on the Stromlo PDS microdensitometer.  Most stars were
    subsequently identified with objects in the ST ScI-NASA-ESO Hubble
    Space Telescope Guide Star Catalog in which positions have an accuracy
    of near +/- 1.0 arcsec.