The Mount Wilson Halo Mapping Project 1975-1985. II. Photometric properties of the Mount Wilson Catalogue of Photographic Magnitudes in Selected Areas 1-139

This paper is partly a review of the history of the making of the Mount Wil son Catalogue of Photographic Magnitudes in Selected Areas 1-139 (hereafter the MWC), begun in 1909 and completed in 1930, and it is partly the presen tation of new photometric results concerning it. Photoelectric photometry o f 435 stars in the 11 Selected Areas of SA 28, 29, 45, 55, 57, 71, 82, 94, 106, 107, and 118 of the MWC is given. The data are used to derive magnitud e corrections to the MWC for these areas. Ten of the areas are in the Galac tic meridional plane (Galactic longitudes of 0 degrees and 180 degrees). Th ese are the same areas used by Becker in his Basel program of star counts f or the study of Galactic structure. The first purpose of the paper is to extend the Basel star counts to fainte r magnitudes. For this, 200 inch photographic plates were measured to the p late limits near B = 22, calibrated with the photoelectric photometry liste d here. A second purpose is to derive certain properties of the catalog. Th e interests are (1) to determine the internal (random) measuring errors of the MWC as a function of magnitude after correcting for the systematic scal e error in each area, (2) to test for a color equation between the correcte d m(pg) (MWC) values and the B-pe system that must be present because of th e difference in reflectivity between silvered and aluminized mirrors, and ( 3) to test for possible distance-to-center corrections of the scale-correct ed MWC magnitudes. Photographic photometry is used to complete the count surveys in each of th e program areas to the limit of the 200 inch plates. Color-magnitude diagra ms are shown for each area, generally complete to V = 20 B-V = 2.0. The wor k is preparatory to an analysis for Galactic structure when the larger data base is available in a program by Majewski using Kitt Peak 4 m plates, epoc h circa 1975, that will be to provide both a deeper count survey in B and V and proper motions for the larger sample.