Copyright © 1981 by the University of Washington Press
In order that users of the charts can know the light levels that characterize each part of M31 charted, we have derived isophotal maps for seventeen of the smaller-scale charts (those near enough to the galaxy to show isophotes). Because of the prohibitive cost of mass producing these as overlays, they are not included in this atlas, but can be obtained at cost on request by writing to the Astronomy Department, University of Washington, Seattle, Washington, 98195, U.S.A.
The isophotal maps were derived from PDS scans made at the Kitt Peak National Observatory and were calibrated by comparison with available photoelectric measures of surface brightness in M31, as described in detail by Hodge and Kennicutt (1981). The plate used, PS 5005 (see table 1), was exposed in the B band of the UBV system and the isophotes are calibrated in B magnitudes per square arc second. The isophotal diagrams are printed to the scale of the corresponding charts and are given in 0.5 magnitude intervals, as indicated on each.